Astrophysics of Galaxies
Unraveling the mysteries of Jets in peculiar NLSy1 galaxies through multi-wavelength variability
Vineet Ojha, Xue-Bing Wu, Luis C. Ho et al. (+4 more)
Radio-quiet narrow-line Seyfert 1
galaxies (RQ-NLSy1s) are generally considered to be dominated by thermal emission from the
accretion disk. However, recurring 37 GHz
radio flares detected from seven RQ-NLSy1s by the Metsahovi
Radio Observatory suggest that non-thermal processes may also contribute to their emission. We present a systematic optical and mid-infrared (MIR) variability study combined with broadband SED modeling to investigate the origin of their flux variations and assess the relative contributions of
accretion disk and possible jet-related components. High-cadence optical light curves in the g, r, and i bands were obtained from ZTF, while long-term MIR light curves in the W1 and W2 bands were taken from WISE. Optical variability was quantified using the FAGN-test, peak-to-peak variability amplitude, and fractional variability, while MIR variability was characterized using
redshift-corrected intrinsic variability amplitudes. Optical variability was examined from intra-night to long-term timescales, and MIR variability on long-term timescales. All RQ-NLSy1s show statistically significant long-term optical variability, with amplitudes increasing toward shorter wavelengths. Three sources exhibit bluer-when-brighter trends and increasing variability amplitudes across the optical bands, indicating a non-thermal contribution. Intrinsic MIR variability is detected in three of the four sources. Significant optical-MIR and MIR intra-band lags are observed, while optical intra-band lags are insignificant. Optical variability amplitudes are anti-correlated with the Eddington ratio and positively correlated with black hole mass. These results suggest that a subset of RQ-NLSy1s hosts weak or intermittent jets contributing to their optical and MIR emission, supported by SED modeling. Coordinated multi-wavelength monitoring is required to better constrain the origin of these variations.
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All authors Vineet Ojha, Xue-Bing Wu, Luis C. Ho, Raj Prince, Joysankar Majumdar, Hum Chand, Chi-Zhuo Wang
High Energy Astrophysical Phenomena · Cross-listed from gr-qc
Optical Signatures of a Schwarzschild Black Hole in a Dehnen-Type Dark Matter Halo
Javokhir Sharipov, Jonibek Khasanov, Pankaj Sheoran et al. (+2 more)
In this paper, the optical effects that occur near a Schwarzschild-like black hole (BH) with a Dehnen-type $(1,4,2)$ dark matter (DM)
halo are explored. We first derive the
photon sphere radius and obtain an analytical expression for the deflection angle in the weak-field regime by applying the Gauss-Bonnet
theorem (GBT). For the strong-field regime, we perform ray-tracing calculations to examine the behavior of light trajectories and determine the corresponding number of orbits. We further compute the BH shadow and gravitational
lensing in a
plasma medium and provide constraints arising from the DM
halo parameters. We also extend our analysis to weak gravitational
lensing within
plasma environments, considering both uniform and singular isothermal sphere (SIS) distributions. We find the analytical expressions for the deflection angle in the presence of
plasma and examine the resulting effects on image magnification. The overall results highlight how DM
halo properties and
plasma characteristics jointly alter observable
lensing signatures.
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All authors Javokhir Sharipov, Jonibek Khasanov, Pankaj Sheoran, Sanjar Shaymatov, Bobomurat Ahmedov
Solar and Stellar Astrophysics
The Y Dwarf Population with HST: unlocking the secrets of our coolest neighbours – III. Near-Infrared Photometry
Clémence Fontanive, Luigi R. Bedin, Mark W. Phillips et al. (+4 more)
Y
dwarfs represent the coldest class of brown
dwarfs, with effective temperatures below 500K, and provide unique analogues to cold
giant exoplanets. We present a large compilation of uniform near-infrared photometry from the Hubble Space
Telescope for 21 Y
dwarfs across multiple WFC3/IR filters, including the F105W, F125W and F160W bands. We employed refined PSF-fitting and calibration procedures to reach photometric uncertainties at the 0.02-0.05 mag level for most targets. Combined with precise parallax measurements, our data reveal well-defined Y-
dwarf sequences in near-infrared colour-magnitude diagrams, observed with a markedly improved tightness. Known photometric trends emerge with minimal scatter, including the continuous redward progression in F125W-F160W with decreasing temperature, and the blueward trend in F105W-F125W with possible hints of a reversal around 350K. Comparisons to the ATMO, Sonora Elf Owl, and Lacy & Burrows atmospheric models highlight systematic discrepancies, in particular F105W-F125W and F105W-F160W colours predicted to be too red. Low-
metallicity grids provide the best fits to the global Y-
dwarf population, although closer inspection across wavelengths shows that these preferences likely reflect compensating effects in missing or incomplete physics rather than true population-level abundances. While some atmospheric diversity is expected among Y
dwarfs, their tight observational sequences and systematic offsets from model predictions reveal that key physical and chemical processes remain inadequately captured in current grids. Our results underscore the importance of high-precision, internally consistent
datasets in robustly tracing the Y-
dwarf cooling sequence and providing the empirical constraints needed to advance theoretical models at the lowest temperatures.
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All authors Clémence Fontanive, Luigi R. Bedin, Mark W. Phillips, Michele Scalco, Loïc Albert, Daniella C. Bardalez Gagliuffi, Beth Biller
Instrumentation and Methods for Astrophysics
NIAC project report: Solar system-scale VLBI to dramatically improve cosmological distance measurements
Matthew McQuinn, Miguel Morales, Casey McGrath et al. (+7 more)
We investigate the feasibility and scientific potential of the
Cosmic Positioning System (CPS), a space mission concept enabling purely
geometric distance measurements to sources at hundreds of megaparsecs by directly detecting electromagnetic wavefront
curvature. CPS consists of a constellation of
radio antennas distributed across the outer
Solar System, operating on baselines of tens of astronomical units. By precisely timing the arrival of repeating fast
radio bursts (FRBs), CPS infers source distances via trilateration – analogous to global
navigation satellite systems such as GPS but on cosmological scales. We show that CPS distance measurements could result in sub-percent constraints on the Hubble constant with even a handful of detections, whereas we predict that 10-100 FRB sources are likely visible. We evaluate dominant sources of uncertainty – wavefront timing precision, interstellar refractive delays, spacecraft positional knowledge, and onboard clock stability – finding these controllable at required levels using near-term technologies. Our nominal design employs five spacecraft with 8 m deployable
antennas, 3-6 GHz receivers with sub-30 K system temperatures, and space-qualified atomic clocks similar to those on GPS satellites, supported by a ground network for ranging calibration and FRB alerts. Beyond
cosmic expansion, CPS may enable frontier measurements in astrophysics and fundamental physics, including constraints on small-scale dark matter structure, microhertz gravitational waves (bridging
pulsar timing arrays and LISA), and the outer
Solar System mass distribution. The most significant viability issue concerns FRB properties at several-GHz frequencies; we recommend observational campaigns to characterize repeating FRBs in this band.
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All authors Matthew McQuinn, Miguel Morales, Casey McGrath, Alyssa Alvarez, Katelyn Glasby, T. Joseph W. Lazio, Kiyoshi Masui, Lyujia Pan, Jonathan Pober, Huangyu Xiao
Instrumentation and Methods for Astrophysics
Spectral response of SPHEREx
Howard Hui, Jamie Bock, Samuel Condon et al. (+31 more)
The Spectro Photometer for the History of the Universe, Epoch of Reionization, and Ices Explorer (SPHEREx) is conducting the first all-sky near infrared spectral survey spanning 0.75 to 5.0um with resolving power R~35 to 130. Linear variable filters mounted in front of six H2RG detectors produce a position dependent spectral response across the focal plane. This paper presents the ground-based spectral calibration of SPHEREx, including the cryogenic apparatus, optical configuration, measurement strategy, analysis pipeline, and resulting calibration products. Monochromatic wavelength scans are used to derive the spectral response function, band center, and resolving power for every pixel. Band centers are measured to better than 1nm for Bands 1 through 4 (0.75 to 3.82um) and better than 10nm for Bands 5 and 6 (3.82 to 5.0um). Out-of-band leakage is negligible for detectors above 1.64um and is present at the percent level below this wavelength. The resolving power is measured to within 5% and agrees with design expectations to within 10%. An on-sky spectrum of the Cat's Eye Nebula (NGC 6543) constructed from repeated observations provides in-flight verification and shows agreement between ground calibrated response and astrophysical emission features. Calibration products, including per-pixel band center and resolving power maps, are released through IPAC to support community use of SPHEREx data. The absolute spectral calibration will continue to improve through in-flight measurements, with further reductions in uncertainty expected for the longest-wavelength bands.
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All authors Howard Hui, Jamie Bock, Samuel Condon, C. Darren Dowell, Woong-Seob Jeong, Young-soo Jo, Phil Korngut, Kenneth Manatt, Chi Nguyen, Hien Nguyen, Stephen Padin, Sung-Joon Park, Jeonghyun Pyo, Yujin Yang, Matt Ashby, Yoonsoo Bach, Tzu-Ching Chang, Yun-Ting Cheng, Yi-Kuan Chiang, Asantha Cooray, Brendan Crill, Ari Cukierman, Olivier Doré, Andreas Faisst, Joe Hora, Jae Hwan Kang, BoMee Lee, Carey Lisse, Dan Masters, Roberta Paladini, Zafar Rustamkulov, Volker Tolls, Michael Werner, Mike Zemcov
Earth and Planetary Astrophysics
Limits on the Post-eclipse Emission Spectrum of HD 80606 b From High-Resolution Spectroscop
Luke Finnerty, Aurora Kesseli, Kyle Pearson et al. (+2 more)
We present Keck/NIRSPEC $K$-band observations of HD 80606 b, one of the most eccentric known
exoplanets. HD 80606 b was observed after secondary eclipse, close to periastron, when the
planet passes within 0.03 AU of HD 80606 and the rapid heating of the atmosphere may lead to extreme chemical changes and a temporary thermal inversion. The rapid change in the planetary radial velocity near periastron is sufficient to enable high-resolution cross-correlation spectroscopy (HRCCS) analysis, which produces a tentative detection ($\rm SNR\sim4$) of HD 80606 b. Injection-recovery tests appear to reject strong thermal inversions near periastron, consistent with recent results from JWST. We also perform atmospheric
retrievals with free parameters for the Pressure-Temperature ($P-T$) profile and with a profile matched to the JWST results, which suggest the presence of absorption features from CH$_4$ and CO. While HD 80606 b is not definitively detected in these data, these results are consistent with JWST observations, which found the post-eclipse atmosphere of HD 80606 b shows weak absorption features from these species. Future observations with higher spectral resolution and/or wider wavelength coverage are needed for a confident atmospheric detection of HD 80606 b via high-resolution spectroscopy alone, but such observations are a challenge to schedule due to the 111-day orbital period.
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All authors Luke Finnerty, Aurora Kesseli, Kyle Pearson, Charles Beichman, Michael P. Fitzgerald
Instrumentation and Methods for Astrophysics
An Interactive Metrics Dashboard for the Keck Observatory Archive
G. Bruce Berriman and Min Phone Myat Zaw
Since 2004, the Keck Observatory Archive (KOA) has operated as a NASA-funded collaboration between the NASA
Exoplanet Science Institute ( NExScI) and the W.M. Keck Observatory. It ingests and serves all data acquired by the twin 10-meter Keck
telescopes on Mauna Kea, Hawaii. In the past three years, KOA has begun a modernization program to replace the architecture and systems used since the archive's creation with a new modern Python-based infrastructure. This infrastructure will position KOA to respond to the rapid growth of new and complex data sets that will be acquired by new instruments now in development, and enable follow-up to identify the deluge of alerts of transient sources expected by new survey
telescopes such as the Vera C. Rubin Observatory. Since 2022, KOA has ingested new data in near-real time, generally within one minute of creation, and has made them immediately accessible to observers through a dedicated web interface. The archive is now deploying a new, scalable, Python-based, VO-compliant query infrastructure built with the Plotly-Dash framework and R-tree indices to speed-up queries by a factor of 20. The project described here exploits the new query infrastructure to develop a dashboard that will return live metrics on the performance and growth of the archive. These metrics assess the current health of the archive and guide planning future hardware and software upgrades. This single dashboard will enable, for example, monitoring of real-time ingestion, as well as studying the long-term growth of the archive. Current methods of gathering metrics that have been in place since the archive opened will not support the archive as it continues to scale. These methods suffer from high latency, are not optimized for on-demand metrics, are scattered among various tools, and are cumbersome to use.
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High Energy Astrophysical Phenomena
Continuous Gravitational Waves from Supersoft X-ray Sources: Promising Targets for deci-Hz Detectors
Mayusree Das, Tomasz Bulik, Sreeta Roy et al. (+1 more)
Supersoft X-ray sources (SSSs) host white
dwarfs (WDs) accreting at rates that sustain steady
nuclear burning, driving rapid mass growth, radial contraction, and
magnetic field amplification. Angular-momentum transfer from the
accretion disk naturally
spins up the WD, while the amplified internal
magnetic field induces a non-axisymmetric deformation in presence of a misaligned rotation. Such WDs emits continuous gravitational waves (CGWs). We model the coupled evolutions of
stellar mass,
spin, and
magnetic structure in accreting WDs in SSSs with MESA, and compute the resulting quadrupolar deformation with the Einstein-Maxwell solver XNS. We show that WDs in SSSs, particularly near the end of thermal timescale mass transfer and close to the Chandrasekhar mass limit, produce CGWs predominantly in the deci-Hz band accessible to planned detectors such as DECIGO, BBO, Deci-Hz, ALIA, and LGWA, and are distinguishable from other
Galactic CGW sources such as AM CVn systems, detached double WDs, and isolated WDs. Well studied SSSs such as CAL 83 and RX J0019+2156 can be detectable, enabling targeted CGW measurements that directly probe WD's internal
magnetic fields and rotation, while blind searches can reveal hundreds of obscured SSSs otherwise missed in soft X-rays and map the hidden population of accreting, rapidly rotating, magnetized WDs in nearby
galaxies. A CGW detection from WDs in SSSs could also identify potential pre-explosion Type Ia progenitors.
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All authors Mayusree Das, Tomasz Bulik, Sreeta Roy, Banibrata Mukhopadhyay
Astrophysics of Galaxies
Black Hole Feedback, Galaxy Quenching and Outflows at Cosmic Dawn: Analysis of the SEEDZ Simulations
Lewis R. Prole, John A. Regan, Daxal Mehta et al. (+13 more)
Here we analyse the growth and feedback effects of massive black holes (MBHs) in the SEEDZ simulations. The most massive black holes grow to masses of $\sim10^{6}$ M$_\odot$ by $z=12.5$ during short bursts of super-Eddington
accretion, sustained over a period of 5-30 Myr. We find that the determining factor that cuts off this initial growth is feedback from the MBH itself, rather than nearby
supernovae or exhausting the available gas reservoir. Our simulations show that for the most actively accreting MBHs, feedback completely evacuates the gas from the host
halo and ejects it into the inter-
galactic medium. Despite implementing a relatively weak feedback model, the energy injected into the gas surrounding the MBH exceeds the binding energy of the
halo. These results either indicate that MBH feedback in the early ($\Lambda$CDM) Universe is much weaker than previously assumed, or that at least some of the high
redshift galaxies we currently observe with JWST formed via a two-step process, whereby a MBH initially quenches its host
galaxy and later reconstitutes its baryonic reservoir, either through mergers with gas rich
galaxies or from
accretion from the
cosmic web. Moreover, the maximum black hole masses that emerge in SEEDZ are effectively set by a combination of MBH feedback modelling and the binding potential of the host
halo. Unless feedback is extremely ineffective at early times (for example if growth is merger dominated rather than
accretion dominated or feedback is contained close to the MBH) then the maximum mass of black holes at
redshift before 12.5 should not significantly exceed $10^6$ M$_\odot$.
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All authors Lewis R. Prole, John A. Regan, Daxal Mehta, Rüdiger Pakmor, Sophie Koudmani, Martin A. Bourne, Simon C. O. Glover, John H. Wise, Ralf S. Klessen, Michael Tremmel, Debora Sijacki, Ricarda S. Beckmann, Martin G. Haehnelt, John Brennan, Pelle van de Bor, Paul C. Clark
High Energy Astrophysical Phenomena
Polarization Signatures of Inspiraling Hotspots around Kerr Black Holes
Pablo Ruales, Delilah E. A. Gates and Alejandro Cárdenas-Avendaño
Polarimetric interferometry is a powerful tool for probing both black hole
accretion physics and the background spacetime. Current models aimed at explaining the observed multiwavelength
flares in Sgr A* often assume hotspots moving on geodesic, Keplerian orbits. In many scenarios, though, a hotspot may instead follow an inspiraling trajectory, potentially transitioning into a plunge toward the black hole. In this work, we present a general framework to simulate the polarized emission from generic equatorial inspiraling hotspots in Kerr spacetime using a parametric four-velocity profile. This parametrization defines a continuous family of flows, ranging from Cunningham's disk model (fixed radius orbits outside the innermost stable circular orbit and plunging motion within the innermost stable circular orbit) to purely radial motion, thereby extending the standard assumptions. Within this framework, we show that inspiral motion produces a distinctive observational signature: a precessing, unwinding
evolution of the polarimetric Stokes Q-U looping pattern, in sharp contrast with the closed Q-U loops associated with stable orbits at a fixed radius. We then explore how the morphology of these signatures depends on black hole
spin, observer inclination, and
magnetic-field configuration. The presented model can be applied to current and near-future interferometric observations of linear polarization, offering a new avenue to probe the physics of matter spiraling inward and the relativistic velocities of plunging
plasma.
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High Energy Astrophysical Phenomena
A Faint Progenitor System for the Faint Supernova 2024vjm
Erez A. Zimmerman, Avishay Gal-Yam, Paul J. Groot et al. (+68 more)
Type Ia
Supernovae (SNe Ia) are well known for their role as standardizable cosmological candles. Their uniformity is credited to their single origin as thermonuclear explosions of White
dwarf (WD)
stars. Nevertheless, some SNe Ia break this regularity. Prominently, the Iax subclass are less energetic and remarkably diverse, raising questions about their progenitor systems. While no progenitor system of a normal SN Ia has ever been detected, a luminous blue
star was identified in pre-explosion images of the site of the bright SN Iax SN 2012Z, suggested to be a helium
giant companion
star acting as a mass donor to a WD SN progenitor. This is in line with models of weak mass
accretion of a WD from a binary companion, producing an explosion that does not fully disrupt the
star. However, these models fail to explain the properties of the faintest Type Iax explosions, suggesting either they originate from other WD binary systems, or even from massive progenitor
stars. Here, we present the faint SN Iax SN 2024vjm - possibly the faintest
supernova observed to date. Using a deep pre-explosion image taken by the recently launched Euclid space mission, we show that its progenitor system must be fainter than the helium
giant SN Iax progenitor candidate of SN 2012Z, as well as that of the luminous red companion or remnant of the faint SN 2008ha, and may require a subdwarf helium
star as a mass donor. The deep image also provides strong arguments against a massive
star origin for this faint
supernova. Our observations argue that SN 2024vjm is a WD explosion, but we find that remarkably faint SNe Iax fade more slowly than bright ones, i.e., they evolve in an opposite manner from the famous Phillips relation that makes regular SNe Ia cosmological candles.
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All authors Erez A. Zimmerman, Avishay Gal-Yam, Paul J. Groot, Eran O. Ofek, Jan van Roestel, Andrea Pastorello, Stefano Valenti, Aravind P. Ravi, Ping Chen, Steve Schulze, Nadejda Blagorodnova, Maxime Wavasseur, Marco A. Gomez-Munoz, Hugo Tranin, Simon de Wet, Giorgos Leloudas, Paul M. Vreeswijk, Lindsey A. Kwok, Michaela Schwab, Saurabh W. Jha, Kate Maguire, David J. Sand, Eric Stringer, Thomas Kupfer, Tamar Faran, Joseph P. Anderson, Jennifer Andrews, Moira Andrews, Avshalom Badash, Steven Bloemen, K. Azalee Bostroem, Ting-Wan Chen, Massimo Della Valle, Georgios Dimitriadis, Yize Dong, Joseph R. Farah, James H. Gillanders, Benjamin Godson, Mariusz Gromadzki, Daichi Hiramatsu, Emily Hoang, D. Andrew Howell, Daryl Janzen, Hanindyo Kuncarayakti, Jiaxuan Li, Joseph D. Lyman, Keiichi Maeda, Mark R. Magee, Curtis McCully, Darshana Mehta, Andrew Milligan, Shane Moran, Yuan Qi Ni, David O'Neill, Jeniveve Pearson, Danielle L. A. Pieterse, Giuliano Pignata, Andrea Reguitti, Daniel E. Reichart, Nicolas Meza Retamal, Rita P. Santos, Simone Scaringi, Manisha Shrestha, Shubham Srivastav, Fiorenzo Stoppa, Bhagya Subrayan, Giorgio Valerin, Xiaofeng Wang, Kathryn Wynn, Ofer Yaron, Weicheng Zang
Astrophysics of Galaxies
Downsizing does not extend to dwarf galaxies: identifying the stellar mass regimes shaped by supernova and AGN feedback
Ilin Lazar, Sugata Kaviraj, Garreth Martin et al. (+10 more)
We explore how the fraction of red (quenched)
galaxies varies in the
dwarf galaxy regime (10^7 MSun < Mstar < 10^9.5 MSun), using a mass-complete sample of ~5900
dwarfs at z<0.15, constructed using deep multi-wavelength data in the COSMOS field. The red fraction decreases steadily until Mstar ~ 10^8.5 MSun and then increases again towards lower
stellar masses. This 'U' shape demonstrates that the traditional notion of 'downsizing' (i.e. that progressively lower mass
galaxies maintain
star formation until later epochs) is incorrect – downsizing does not continue uninterrupted into the
dwarf regime. The U shape persists regardless of environment, indicating that it is driven by internal processes rather than external environment-driven mechanisms. Our results suggest that, at Mstar < 10^8 MSun, the quenching of
star formation is dominated by
supernova (SN) feedback and becomes more effective with decreasing
stellar mass, as the potential well becomes shallower. At Mstar > 10^9 MSun, the quenching is driven by a mix of SN feedback and AGN feedback (which becomes more effective with increasing
stellar mass, as central black holes become more massive). The processes that quench
star formation are least effective in the range 10^8 MSun < Mstar < 10^9 MSun, likely because the potential well is deep enough to weaken the impact of SN feedback, while the effect of AGN feedback is still insignificant. The cosmological simulations tested here do not match the details of how the red fraction varies as a function of
stellar mass – we propose that the red fraction vs
stellar mass relation (particularly in the
dwarf regime) is a powerful calibrator for the processes that regulate
star formation in
galaxy formation models.
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All authors Ilin Lazar, Sugata Kaviraj, Garreth Martin, Christopher J. Conselice, Sophie Koudmani, Aaron E. Watkins, Sukyoung K. Yi, Darshan Kakkad, Thomas M. Sedgwick, Yohan Dubois, Julien E. G. Devriendt, Katarina Kraljic, Sebastien Peirani
Cosmology and Nongalactic Astrophysics · Cross-listed from hep-ph
Tuning the violins: dark sector phase transition models for the PTA signal
Torsten Bringmann, Thomas Konstandin, Jonas Matuszak et al. (+2 more)
First-order phase transitions in a dark sector have been invoked as an intriguing possibility to explain the observed
stochastic gravitational wave background at nanohertz frequencies. Here we perform a comprehensive study of the generic requirements for such a phase transition to explain the observed signal while being consistent with all relevant constraints. We consider three broad model classes for strong first-order transitions, realised by an Abelian dark
Higgs boson, a two-step phase transition involving two scalar singlets, and a conformal scalar field with loop-induced
symmetry breaking, respectively. We discuss the tuning that is required to successfully explain the
Pulsar Timing Array (PTA) signal in each of these cases, and highlight the underlying physical mechanisms. We conclude that all three scenarios can in principle describe the data, but that conformal models stand out as the most generic, and least tuned, explanation. Future observations by the PTA collaborations and
collider experiments will be crucial to test the viability of this hypothesis, and to further narrow in on the model parameters, if the PTA signal is indeed due to a strong first-order phase transition.
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All authors Torsten Bringmann, Thomas Konstandin, Jonas Matuszak, Kai Schmidt-Hoberg, Carlo Tasillo
Astrophysics of Galaxies
All the Massive Galaxy Overdensities during Reionization: JWST Rest-Frame Optical Selection Reveals Young, Chemically Evolved Galaxies Embedded in Dense, Neutral Gas at z > 5
Chamilla Terp, Kasper E. Heintz, Jorryt Matthee et al. (+7 more)
The high-
redshift progenitors of present-day
galaxy clusters are believed to substantially contribute to the global
star-formation rate density and drive the large-scale reionization of the Universe. Here we present a blind and unbiased search for and characterization of
galaxy overdensities during the reionization epoch at
redshifts $z\sim 5.5-7$, based on rest-frame optical JWST/NIRCam grism spectroscopy of the Abell\,2744
lensing field as part of the JWST-ALT survey. Using a physically-motivated, cosmological inference Friends-of-Friends (FoF)
algorithm, we identify six
galaxy overdensities, including five robust systems at $z=5.66$ to $6.77$. They are all characterized by total
halo masses $M_{\rm halo} \gtrsim 10^{11}\,M_{\odot}$ inferred from a range of proxies. We find that the
galaxy members in these overdense environments are on average less massive though equally metal-rich, and generally comprised of younger
stellar populations as indicated from their bluer spectral slopes less prominent Balmer breaks, than field
galaxies at similar
redshifts. Further, we use this novel rest-frame optical selection of
galaxy proto-clusters to infer the fraction and 3D distribution of strong Lyman-$\alpha$ emitters (LAEs) and damped Lyman-$\alpha$ absorbers (DLAs) in the overdensity environments. We find that two out of six
galaxy overdensities have excess \hi\ absorption compared to the field-average, while the other four are consistent within their large scatter in density. These results present the first direct observational constraints on the
tomography of the dense, neutral gas reservoirs in large-scale
galaxy overdensities at $z>5$ and highlight the limitations of pre-JWST searches for reionization-era
galaxy overdensities relying on the detection of strong LAEs alone.[Abridged]
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All authors Chamilla Terp, Kasper E. Heintz, Jorryt Matthee, Rohan P. Naidu, Pascal A. Oesch, Callum Witten, Daichi Kashino, Clara L. Pollock, Claudia Di Cesare, Alberto Torralba
Cosmology and Nongalactic Astrophysics · Cross-listed from gr-qc
Systematic biases in parameter estimation on LISA binaries. II. The effect of excluding higher harmonics for spin-aligned, high-mass binaries
Sophia Yi, Francesco Iacovelli, Emanuele Berti et al. (+4 more)
The
Laser Interferometer Space
Antenna (LISA) will observe massive black hole binaries (MBHBs) with astoundingly high signal-to-noise ratio, leaving parameter estimation with these signals susceptible to seemingly small waveform errors. Of particular concern for MBHBs are errors due to neglected higher-order modes. We extend Yi et al. [arXiv:2502.12237] to examine errors due to neglected higher-order modes for MBHBs with nonzero (aligned) progenitor
spins and total mass up to $10^8\,M_\odot$. For these very massive systems, there can be regions of parameter space in which the $(\ell, |m|)=(2,\,2)$ modes are no longer dominant with respect to higher-order ones. We find that the extent of systematic bias can change significantly when varying the progenitor
spins of the binary. We also find that for the heaviest, and therefore shortest, MBHB signals, slight systematic errors can cause severe misinference of the sky localization parameters. We propose an improved likelihood optimization scheme with respect to previous work as a way to predict these effects in a computationally efficient manner.
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All authors Sophia Yi, Francesco Iacovelli, Emanuele Berti, Rohit S. Chandramouli, Sylvain Marsat, Digvijay Wadekar, Nicolás Yunes
Astrophysics of Galaxies
Multi-wavelength morphology and dust emission in low-redshift dwarf galaxies in COSMOS-Web with HST and JWST
D. Kakkad, I. Lazar, S. Harish et al. (+18 more)
Low-mass or
dwarf galaxies (M$_{\ast}<10^{9}$ M${\odot}$) are abundant in the Universe, yet their formation and
evolution remain poorly understood. Their enhanced sensitivity to feedback from
star formation and active
galactic nuclei (AGN) make them excellent laboratories to test whether feedback prescriptions in cosmological simulations accurately reproduce their interstellar medium (ISM) properties. We present JWST/NIRCam and MIRI imaging of nine
dwarf galaxies from COSMOS-Web survey at
redshift $z<0.08$, with
star formation rates ranging from 0.003-0.3 M${\odot}$ yr$^{-1}$ and
stellar masses of log M$_{\ast}\sim8-9$ M$_{\odot}$. The detection rate with both NIRCam and MIRI is 100%, indicating that these
dwarfs possess substantial ISM content. The detected sample includes a roughly equal mix of early-type and late-type
dwarfs, suggesting that it is representative of the broader
dwarf galaxy population in low-density environments. We find that the observed MIRI flux distributions are comparable to forward-modelled flux distributions of mass-matched simulated
galaxies in TNG50. We further conduct a multi-wavelength morphological analysis complementing the JWST NIRCam and MIRI imaging with archival HST/ACS data, employing the CAS (concentration, asymmetry, smoothness) framework. Among the multi-wavelength images, MIRI exhibits the largest variation in CAS parameters, likely due to
dust lanes and clumps in several
galaxies, also suggested by Spectral Energy Distribution (SED) fitting. This suggests that the
dust content in these systems may be higher than those implied by rest-frame optical or near-infrared observations alone. Upcoming UV/optical and mid-infrared spectroscopic follow-up will be critical for constraining the gas kinematics and
dust grain properties of
dwarf galaxies in low-density environments such as COSMOS.
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All authors D. Kakkad, I. Lazar, S. Harish, B. Bichang'a, R. K. Cochrane, S. Kaviraj, A. E. Watkins, G. Martin, S. Koudmani, Andrew J. Battisti, Caitlin Casey, Maximilien Franco, G. Gozaliasl, M. Hirschmann, Jeyhan Kartaltepe, A. A. Khostovan, Anton Koekemoer, Daizhong Liu, Henry Joy McCracken, Jason Rhodes, Brant Robertson
High Energy Astrophysical Phenomena
An Exploration of the Equation of State Dependence of Core-Collapse Supernova Explosion Outcomes and Signatures
Aleksandr Rusakov, Adam S. Burrows, Tianshu Wang et al. (+1 more)
We explore, using a state-of-the-art simulation code in 3D and to late enough times to witness final observables, the dependence of core-collapse
supernova explosions on the
nuclear equation of state. Going beyond questions of explodability, we compare final explosion energies, nucleosynthetic yields,
recoil kicks, and gravitational-wave and
neutrino signatures using the SFHo and DD2
nuclear equations of state (EOS) for a 9-$M_{\odot}$/
solar-
metallicity progenitor
star. The DD2 EOS is stiffer and has a lower effective nucleon mass. The result is a more extended protoneutron
star (PNS) and lower central densities. As a consequence, the mean
neutrino energies, final explosion energy, and
recoil kick speed are lower. Moreover, the
evolution of PNS convection differs between the two EOS models in significant ways. This translates in part into interestingly altered
neutrino “light" curves and noticeably altered gravitational-wave signal strengths and frequency characteristics that may be diagnostic. The faster exploding model (SFHo) yields slightly more
neutron-rich ejecta and more species with atomic weights between 60 and 90 and a weak r-process. However, this is merely a preliminary study. The next step is a more comprehensive and multi-progenitor set of 3D
supernova simulations for various EOSes to late times when the observables have asymptoted. Such a future investigation will have a direct bearing on the
neutron star and black hole birth mass functions and the quest towards a fully quantitative theory of
supernova observables.
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All authors Aleksandr Rusakov, Adam S. Burrows, Tianshu Wang, David Vartanyan
Solar and Stellar Astrophysics
The seismic diversity of four successive solar cycle minima as observed by the Birmingham Solar-Oscillations Network (BiSON)
Sarbani Basu, William J. Chaplin, Rachel Howe et al. (+3 more)
We have used data collected by the Birmingham
Solar-Oscillations Network (BiSON) to perform a helioseismic diagnosis of changes to the Sun's internal structure between four successive
solar cycle minima, beginning with the minimum at the end of cycle 21 and ending with the recent minimum at the beginning of cycle 25. The unique duration of the BiSON database makes such a study possible. We used the low-degree BiSON p-mode frequencies to constrain structural changes between minima in the layers above $\approx 0.9 R_{\odot}$. We accomplished this by examining variations in the HeII ionisation zone signature; and by inverting the frequency differences to infer changes in the sound speed. Additionally, we employed frequency differences between various
solar models that had subtle modifications to their internal structures to facilitate analysis of the observations. We find evidence for small, but marginally significant, changes in structure between different minima. The HeII signature was larger, and the sound speed in the range $\approx 0.93$ to $0.97 R_{\odot}$ was slightly higher, during the cycle 23/24 minimum, than during the other minima. The cycle 23/24 minimum was the deepest, as measured by proxies of global
solar activity. These findings are consistent with
magnetic flux levels having been lower in this minimum than the others, resulting in a higher gas pressure, higher temperatures, and higher sound speed. Our results demonstrate the potential of using asteroseismic data to perform similar analyses on other
solar-type
stars.
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All authors Sarbani Basu, William J. Chaplin, Rachel Howe, Yvonne Elsworth, Steven J. Hale, Eleanor Murray
Solar and Stellar Astrophysics
Evaluating the $\Sigma$-effect Model of the Solar Hemispherical Helicity Bias via Direct Numerical Simulations
Jacob B. Noone Wade and Nicholas H. Brummell
The
Solar Hemispherical Helicity Rule(s) (SHHR) is a term used to represent a bias observed in proxies for the
magnetic helicity in active regions at the
solar surface. The SHHR states that predominantly negative
magnetic helicity is observed in active regions in the northern hemisphere, whereas predominantly positive is found in the southern. The $\Sigma$-effect model of \cite{longcope1998flux} is one of the most cited models for the explanation of the SHHR. In this model, the
magnetic structures derive the bias in their
magnetic helicity from the kinetic helicity of the turbulent convection through which they travel, where the latter is handed owing to the rotational influence of the
star. The original paper built an elegant mathematical model for the dynamics of thin flux tubes influenced by parameterized helical
turbulence. Here, we attempt to explore the conceptual ideas of this original simplified model using fully-nonlinear, three-dimensional, Cartesian-domain simulations of isolated, finite cross-sectional, twisted
magnetic flux structures rising though rotating, overshooting, turbulent compressible convection. We look for evidence of a correlation between the kinetic helicity content of the
turbulence and the evolving
magnetic helicity of the structures. We find little evidence of such a relationship, and do not even find any clear hemispheric dependence. Although these simulations are far from a perfect representation of the ideas, this work raises many questions about the potential efficacy of the $\Sigma$-effect in reality.
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Solar and Stellar Astrophysics
Granulation signatures as seen by Kepler short-cadence data. I. A decoupling between granulation and oscillation timescales for dwarfs
Jens R. Larsen, Mia S. Lundkvist, Martin B. Nielsen et al. (+3 more)
Granulation is the observable signature of convection in envelopes of low-mass
stars, forming the background in
stellar power spectra. While well-studied in evolved
giants, granulation on the MS has received less
attention. We here study and characterise granulation signatures of MS and SGB
stars, extending previous studies of
giants to provide a continuous physical picture across evolutionary stages. We analyse 753 Kepler short-cadence
stars using a
Bayesian nested-sampling framework to evaluate three background descriptions and compare model preferences. This yields full posterior distributions for all parameters, enabling robust comparisons across a diverse
stellar sample. No universal preference between background models is found. Assuming a Gaussian oscillation envelope, $\nu_\mathrm{max}$ estimates are sensitive to model misspecification, with the resulting systematics exceeding the formal uncertainties. The envelope width scales with $\nu_\mathrm{max}$ across models and shows a dependence on effective temperature. Total granulation amplitudes in
dwarfs broadly follow
giant-based scalings, however a decoupling appears between the timescale of the primary granulation and the oscillations for MS
stars cooler than the Sun. The prolonged granulation timescale is reproduced by 3D simulations of a K-
dwarf, driven by reduced convective velocities due to more efficient convective energy transport in denser envelopes. The prolonged granulation timescale increases the frequency separation to the oscillation excess, potentially aiding seismic detectability, while the reduced convective velocities may influence the excitation of
stellar oscillations and relate to the low amplitudes observed in cool
dwarfs. Finally, we contribute a
dataset linking granulation, oscillations, and
stellar parameters, providing a foundation for future investigations into their interdependence across the HR diagram.
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All authors Jens R. Larsen, Mia S. Lundkvist, Martin B. Nielsen, Guy R. Davies, Yixiao Zhou, Mikkel N. Lund
Earth and Planetary Astrophysics
Indications of Rapid Dust Formation in the Inner Region of a Protoplanetary Disk
Thanawuth Thanathibodee, Catherine Espaillat, Nuria Calvet et al. (+4 more)
We report a significant increase in mid-infrared emission $\leq10$ $\mu$m in a transitional disk. The 2024 JWST/MIRI observation of the disk around CVSO 1942 reveals flux increase by a factor of two at $\lambda\leq10$ $\mu$m, compared to the near photospheric flux level observed with Spitzer/IRS in 2005. No significant change in flux at $\gtrsim15$ $\mu$m is detected in the spectra. Comparing the MIRI/MRS spectrum and NEOWISE photometry, we found that this $\leq10$ $\mu$m flux increase occurs on a timescale of 2 weeks and is consistent with the presence of warm (1,400 K), optically thick, large ($\gtrsim1$ $\mu$m)
dust grains near the
dust sublimation radius. We propose that this rapid
dust appearance may indicate in situ
dust formation, possibly from planetesimal collisions in the inner disk.
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All authors Thanawuth Thanathibodee, Catherine Espaillat, Nuria Calvet, Zhaohuan Zhu, Julalak Nammanee, Caeley Pittman, Maire Volz
Solar and Stellar Astrophysics
Is the nitrogen-rich source PN K4-47 a true planetary nebula?
Thomas Steinmetz, Tomasz Kaminski, David Jones et al. (+3 more)
PN K4-47 is a young planetary nebula that exhibits shock-excited bipolar lobes and a complex molecular environment, with the highest number of molecules detected within a planetary nebula. It has been questioned whether K4-47 is indeed a `typical' planetary nebula, or may be more exotic in nature. We examine this question using optical imaging and spectroscopy, and sub-millimetre and
radio interferometry. Our observations spatially resolve the sub-millimetre environment of K4-47 for the first time. We find elongated CO (2-1) emission along a similar PA to the optical bipolar
outflow. We derive a distance upper limit of 6 kpc to the source. The source hosts a fast ($\sim$350 km s$^{-1}$) bipolar optical
outflow, and a slow (~50-60 km s$^{-1}$) molecular
outflow along a similar PA. The
outflow velocity indicates an age of 336 $\pm$ 119 yr. We also find that the excitation temperature and density of the atomic gas is~20 kK and 2800 cm$^{-3}$, respectively. The elemental and isotopic enrichment of K4-47 infers an AGB progenitor mass of 4-6 M$_{\odot}$, which corresponds to a white
dwarf mass of ~1 M$_{\odot}$, following the initial-final mass relation for white
dwarfs. We find that the core of K4-47 must contain 10$^{-2}$ M$_{\odot}$ of
dust to explain the extinction, and that photoionisation alone cannot explain the excitation of the atomic gas. We instead require an additional heating mechanism, with shocks a likely scenario. It is likely that the progenitor
star of K4-47 was a J-type carbon AGB
star, which formed the molecular and dusty circumstellar environment. The bipolar
outflow is later triggered, punching through the circumstellar environment, producing shocks, and shaping the environment into the elongated structure seen in the sub-millimetre. We therefore classify K4-47 as a genuine, if unusual, planetary nebula.
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All authors Thomas Steinmetz, Tomasz Kaminski, David Jones, Marcin Hajduk, Denise R. Goncalves, Stavros Akras
Earth and Planetary Astrophysics
Two Robust Interstellar Meteor Candidates in the Post-2018 CNEOS Fireball Database
Richard Cloete and Abraham Loeb
We report the identification of two previously unrecognized interstellar meteor candidates in the NASA CNEOS fireball database. Using the empirically calibrated low-discrepancy uncertainty model of Peña-Asensio et al.\ (2025) for post-2018 CNEOS velocity accuracy (1$\sigma$: speed 0.55~km~s$^{-1}$, right ascension 1.35$^\circ$, declination 0.84$^\circ$), we transform CNEOS velocity vectors to heliocentric orbits and assess interstellar candidacy via $10^{6}$-draw Monte Carlo simulations. Two post-2018 events have heliocentric speeds robustly exceeding the
Solar System escape speed. CNEOS-22 (2022-07-28; 6.0$^\circ$S, 86.9$^\circ$W; eastern tropical Pacific) has $v_{\rm hel}=46.98$~km~s$^{-1}$, exceeding escape by $\Delta = 5.18 \pm 0.60$~km~s$^{-1}$ ($z_{\Delta}=8.7\sigma$), with interstellar speed $v_{\infty,\odot}=21.5$~km~s$^{-1}$. CNEOS-25 (2025-02-12; 73.4$^\circ$N, 49.3$^\circ$E; Barents Sea) has $v_{\rm hel}=45.63$~km~s$^{-1}$, exceeding escape by $\Delta = 3.22 \pm 0.58$~km~s$^{-1}$ ($z_{\Delta}=5.5\sigma$), with $v_{\infty,\odot}=16.9$~km~s$^{-1}$. For both events, none of $10^{6}$ realizations yield a gravitationally bound orbit ($p_{\rm bound} < 3\times 10^{-6}$). The adopted error model would need to underestimate the true uncertainties by factors of 5–9 for either candidate to be marginally bound.
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High Energy Astrophysical Phenomena
Microquasar Remnants as Pevatrons Illuminating the Galactic Cosmic Ray Knee
Bing Theodore Zhang and Shiqi Yu
Microquasars are primary candidates for
Galactic PeVatrons, yet their collective contribution to the
cosmic ray (CR) “knee" remains poorly understood. We investigate this contribution by simulating anisotropic diffusive propagation through the
Galactic magnetic field. Our results demonstrate that spatial
alignment and
magnetic connectivity between source locations and the
solar neighborhood govern the local flux: sources aligned with local
magnetic field lines yield pronounced flux enhancements, whereas magnetically disconnected locations are strongly suppressed. We find that the characteristic
proton bump near PeV is robust across random realizations of the
Galactic microquasar remnant population, with as few as four nearby remnants accounting for 50% of the observed PeV flux. Our findings suggest that the integrated history of microquasar remnants, governed by source temporal and spatial distribution and
magnetic transport, naturally populates the observed CR “knee”.
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Earth and Planetary Astrophysics
RedDots: Multiplanet system around M dwarf GJ 887 in the solar neighborhood
C. Hartogh, S. V. Jeffers, S. Dreizler et al. (+7 more)
GJ 887 is a bright M
dwarf in the
solar neighborhood with two currently reported nontransiting
exoplanets with periods of $9~\mathrm{d}$ and $21~\mathrm{d,}$ along with an additional unconfirmed signal at $50~\mathrm{d}$. We reanalyzed the system with 101 new HARPS and 12 new ESPRESSO radial velocities (RVs) secured with a cadence to confirm or refute the origin of the $50~\mathrm{d}$ signal. To do so, we searched for signals related to
stellar activity in photometric data and spectroscopic indicators. We modeled the
stellar activity in the RVs with Gaussian processes (GPs). With the
Bayesian analysis, we confirmed a four-
planet model, including the two previously known
planets at periods of $9.2619\pm0.0005~\mathrm{d}$ and $21.784\pm0.004~\mathrm{d,}$ as well as two newly confirmed
exoplanets: an Earth-mass
planet, with a $4.42490\pm0.00014~\mathrm{d}$ period and a sub-meter-per-second amplitude, and a super-Earth with a $50.77\pm0.05~\mathrm{d}$ period located in the habitable zone (HZ). This super-Earth is the second closest
planet in the HZ, after Proxima Cen b. We found an additional signal in a 2:1 resonance with the $4.4~\mathrm{d}$
planet at $2.21661\pm0.00010~\mathrm{d}$ with an amplitude of $0.37\pm0.09~\mathrm{m/s}$, which could be related to an additional
planet. However, other explanations of its origin are also plausible. This signal remains a candidate, as further investigation is required to confirm its true nature. If the signal is caused by a
planet, its minimum mass would be half that of Earth. We measured the
stellar rotation period with the characteristic periodic timescale of the GP. We found a period of $38.7\pm0.5~\mathrm{d}$, which is consistent with the rotation period determined from photometry and other activity indices.
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All authors C. Hartogh, S. V. Jeffers, S. Dreizler, J. R. Barnes, C. A. Haswell, F. Liebing, A. Collier Cameron, P. Gorrini, F. Del Sordo, P. Cortés-Zuleta
Cosmology and Nongalactic Astrophysics
Hints of sign-changing scalar field energy density and a transient acceleration phase at $z\sim 2$ from model-agnostic reconstructions
Özgür Akarsu, Maria Caruana, Konstantinos F. Dialektopoulos et al. (+3 more)
We present a data-driven reconstruction of the late-time expansion history and its implications for dark-energy dynamics. Modeling the reduced Hubble rate with a node-based Gaussian-process-kernel interpolant, we constrain the reconstruction using CC, Pantheon+ SNIa, BAO data from SDSS and DESI, transversal BAO data, and external $H_0$ priors (SH0ES and H0DN). Assuming GR at the background level, we map the reconstructed kinematics onto a dark-energy fluid and a scalar-field description, yielding the total potential and kinetic contributions that reproduce the inferred $H(z)$. To interpret the reconstruction, we consider both a minimal single-field model (canonical or phantom) and a two-field (quintom) system consisting of one canonical and one phantom scalar field (or families). Within the GR-based effective-fluid mapping, the inferred dark-energy density changes sign for all
dataset combinations explored, transitioning from $\rho_{\rm DE}<0$ at higher
redshift to $\rho_{\rm DE}>0$ toward the present, and defining a transition
redshift $z_\dagger$ by $\rho_{\rm DE}(z_\dagger)=0$. A single canonical scalar cannot realize such a smooth
evolution during expansion, whereas a phantom field or a two-field quintom framework can accommodate the required behavior; in particular, the two-field system permits smooth phantom-divide crossings at finite $\rho_{\rm DE}>0$ and distinguishes them from the separate notion of a density zero crossing. The reconstructed kinematics admit intermediate-
redshift structure in some combinations, including hints of an additional accelerated-expansion interval around $z\sim 1.7$–$2.3$. The present-day equation of state remains close to a cosmological constant: combinations including
supernovae give $w_0\simeq -1$, while combinations without
supernovae but with an external $H_0$ prior show only a mild preference for $w_0<-1$ at the $\sim1.5$–$1.7\sigma$ level.
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All authors Özgür Akarsu, Maria Caruana, Konstantinos F. Dialektopoulos, Luis A. Escamilla, Emre O. Kahya, Jackson Levi Said
High Energy Astrophysical Phenomena
The Reawakening of 4U 1755-338 after 25 Years of Quiescence: Spectro-temporal Analysis Using Multi-instrument X-ray Data
Geethu Prabhakar and Samir Mandal
The black hole X-ray binary 4U 1755$-$338 underwent an outburst in 2020 after 25 years of quiescence. The comprehensive spectral analysis revealed that the system has a low interstellar neutral hydrogen column density of $0.34\pm0.01 \times$10$^{22}$ cm$^{-2}$. The outburst began with a low mass-
accretion rate and was characterized as a low-luminosity outburst. The radius of the inner
accretion disc remained constant throughout the outburst. Additionally, a growing neutral medium with constant density was detected in the local environment of 4U 1755$-$338.The hardness-intensity diagram (HID) did not follow the standard q-shaped pattern, indicating a non-canonical outburst. Instead, the HID showed a correlated
evolution of hardness and source flux, suggesting a thermal disc origin of the flux. A wideband spectral analysis was performed using simultaneous NICER-NuSTAR data in two frameworks, based on kerrbb and bhspec. The results of bhspec (kerrbb) based modeling indicate that 4U 1755$-$338 is a high-inclination system, $67.44_{-3.03}^{+9.75}$ ($75.25_{-4.68}^{+5.59}$) degrees, and harbors a moderately spinning black hole with a
spin parameter of $0.78_{-0.14}^{+0.02}$ ($0.50_{-0.43}^{+0.19}$) and a mass of $3.37_{-1.04}^{+0.45} (3.28_{-1.1}^{+1.7})M_{\odot}$ respectively. The inferred key parameters: black hole mass,
spin, and system inclination are consistent across both modeling approaches. No reflection features were detected in the spectra of 4U 1755$-$338. The high spectral index, the blackbody nature ($L\propto T^4$) of the hardness ratio, the absence of reflection signatures, and the weak variability in the power density spectra indicate that the source remained in the high/soft state throughout the outburst.
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High Energy Astrophysical Phenomena
On the Deepest Search for Galactic Center Pulsars and an Examination of an Intriguing Millisecond Pulsar Candidate
Karen I. Perez, Vishal Gajjar, Slavko Bogdanov et al. (+6 more)
We report results of one of the most sensitive
pulsar surveys to date targeting the innermost region of the
Galactic Center (GC) using the Robert C. Byrd Green Bank
Telescope (GBT) at X-band (8–12GHz) using data from the Breakthrough Listen initiative. In total, we collected 9.5 hr of data covering the wider $\sim 8'$ diameter of the GC bulge, and 11 hr on the inner $1.4'$ region between 2021 May and 2023 December. We conducted a comprehensive
Fourier-domain periodicity search targeting both canonical
pulsars (CPs) and millisecond
pulsars (MSPs), using constant and linearly changing acceleration searches to improve sensitivity to compact binaries. Assuming weak scattering, our searches reached luminosity limits of $L_{\rm min} \approx 0.14~{\rm mJy~kpc^{2}}$ for CPs and $L_{\rm min} \approx 0.26~{\rm mJy~kpc^{2}}$ for MSPs – sensitive enough to detect the most luminous
pulsars expected in the GC. Among 5,282 signal candidates, we identify an interesting 8.19 ms MSP candidate (DM of 2775 pc cm$^{-3}$), persistent in time and frequency across a 1-hr scan at a flux density of $S_{\rm min} \approx 0.007~{\rm mJy}$. We introduce a novel randomization test for evaluating candidate significance against noise fluctuations, including signal persistence via Kolmogorov-Smirnov tests and flux-vs-DM behavior. We are unable to make a definitive claim about the candidate due to a mixed degree of confidence from these tests and, more broadly, its non-detection in subsequent observations. This deepens the ongoing missing
pulsar problem in the GC, reinforcing the idea that strong scattering and/or extreme orbital dynamics may obscure
pulsar signals in this region.
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All authors Karen I. Perez, Vishal Gajjar, Slavko Bogdanov, Jules P. Halpern, Paul B. Demorest, Steve Croft, Matt Lebofsky, David H. E. MacMahon, Andrew P. V. Siemion
High Energy Astrophysical Phenomena
Seasonal Variation of Polar Ice: Implications for Ultrahigh Energy Neutrino Detectors
Alexander Kyriacou, Steven Prohira and Dave Besson
The upper $100 \, \mathrm{m}$ to $150 \, \mathrm{m}$ of the polar ice sheet, called the firn, has a time-dependent density due to seasonal variations in the surface temperature, snow accumulation and surface melt events. We present RF simulations of an in-ice
neutrino-induced
radio source that show that these density anomalies create variations in the amplitude and propagation times of
radio signals propagating through the polar firn at Summit, Greenland. The received power from signals generated in the ice that refract within the upper ${\sim} 15 \, \mathrm{m}$ firn are subject to a seasonal variation on the order of 10%. These variations result in an inherent and geometry dependent background uncertainty on the reconstructed
neutrino energy and arrival direction for detectors using ice as a detection medium.
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Solar and Stellar Astrophysics
Discovery of a double white dwarf in the Galactic globular cluster NGC 6397
Fabian Göttgens, Marilyn Latour, Ulrich Heber et al. (+4 more)
Binaries in the cores of globular clusters are known to prevent the gravitational collapse of the cluster, and simulations predict that the core of NGC 6397 contains a large number of white
dwarfs (WDs), of which many are expected to be part of a binary system. In this work, we report the discovery of a compact binary system consisting of two WDs in the centre of the
Galactic globular cluster NGC 6397. The system, known in the literature as NF1, was observed as part of a MUSE radial-velocity survey aiming at characterizing the binary population in the centre of NGC 6397. The spectral analysis of NF1 provides an effective temperature of 16000 K and a surface
gravity (log g) of 5.72 (cgs), which is consistent with an extremely low-mass He-core WD nature. This is further supported by the mass of 0.23 +/- 0.03 Msun obtained from fitting the
star's spectral energy distribution using its HST magnitude in various filters. The system has a circular orbit with a period of 0.54 days. The radial velocities show a large semi-amplitude of 200 km/s, implying a minimum mass of 0.78 Msun for the invisible companion, which is likely another WD, or a
neutron star if the inclination of the system is smaller than about 50 deg. Some significant residuals in radial velocity remain with our best orbital solution and we tested whether a model with a third body can explain these deviations. While this possibility seems promising, additional measurements are needed to confirm whether the
star is actually part of a triple system.
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All authors Fabian Göttgens, Marilyn Latour, Ulrich Heber, Sebastian Kamann, Kyle Kremer, Sven Martens, Stefan Dreizler