High Energy Astrophysical Phenomena
XMM-Newton Observations of Flares and a Possible Pulse Dropout in the Supergiant X-ray binary 4U 1909+07
Joel B. Coley, Ralf Ballhausen, McKinley Brumback et al. (+9 more)
We report on a pair of X-ray Multi-Mirror Mission (XMM-Newton) observations of the Supergiant X-ray binary 4U 1909+07, which were performed on 2021 October 3 and 2021 October 8, respectively. We measure the
neutron star rotation period in each observation to be $\sim$602.62 s. This continues a long
spin-up trend that has persisted since 2001 where the
neutron star spin period was found to be $\sim$604.66 s. In our timing analysis, we observe strong variations in the amplitude of the 1–10 keV pulse profile as a function of time, and for the first time we find a low flux interval extending for a single pulse period in which pulsations are no longer detected. We interpret this low flux interval as a pulse dropout similar to those observed in Vela X-1 and GX 301-2, which were each explained by a low-density cavity in the wind driving the propeller effect. In our time-resolved spectral analysis, we observed the spectral continuum, which can be described as an absorbed power law modified by a high-energy cutoff, to significantly soften during the pulse-dropout phase. No evidence of an increasing absorption column density was found. The observed softening in 4U 1909+07 also supports an interpretation that the observed pulse dropout may be driven by the propeller effect, but the quasi-spherical settling
accretion regime cannot be ruled out.
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All authors Joel B. Coley, Ralf Ballhausen, McKinley Brumback, Robin H.D. Corbet, Camille M. Diez, Felix Fuerst, Nazma Islam, Gaurava K. Jaisawal, Peter Kretschmar, Christian Malacaria, Katja Pottschmidt, Pragati Pradhan
Astrophysics of Galaxies
Right round: onset and long-term evolution of rotation in star clusters
E. Dalessandro, A. Della Croce, E. Vesperini et al. (+4 more)
We present the results of a detailed kinematic analysis of a significant fraction of the known population of
Galactic star clusters aimed at constraining the physical mechanisms driving the onset and
evolution of cluster rotation. Our study reveals for the very first time the presence of rotation in clusters at any age, with about $25\%-30\%$ of systems in the sample showing significant evidence of rotation. This result increases by a factor of $\sim5$ the number of clusters identified as rotators so far and it finally enables an observational reading of cluster rotation as a function of time. Young ($<500$ Myr) clusters show a larger range of rotation velocities than older systems. In addition, at young ages we observe a significantly larger fraction ($50\%-60\%$) of rotating systems than at older ones ($\sim 15\%$). These purely empirical results are compatible with rotation being imprinted during the very early stages of cluster formation and early
evolution and then being progressively erased by the long-term effects of dynamical
evolution. For the sub-sample of clusters for which we were able to perform a full 3D analysis, we calculated the angle between the internal rotation axis and that of the cluster orbital motion. Interestingly, while for clusters with an age smaller than their orbital period we observe similar fractions of prograde and retrograde systems, more evolved clusters appear to be preferentially prograde. We argue that such a behavior is in qualitative agreement with the expectations for the
evolution of systems in which
primordial rotation was imprinted by the parent molecular cloud and/or by the following hierarchical cluster assembly processes, and in which internal cluster dynamics and interactions with the
Galactic field have induced a torque-driven
alignment between cluster rotation and orbital motion.
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All authors E. Dalessandro, A. Della Croce, E. Vesperini, M. Cadelano, S. Leanza, G. Ettorre, M. Hughes
Instrumentation and Methods for Astrophysics
The Cosmological Simulation Code OpenGadget3 - Implementation of Self-Interacting Dark Matter
Moritz S. Fischer, Marc Wiertel, Cenanda Arido et al. (+7 more)
Dark matter (DM) could be subject to non-gravitational self-interactions which is relevant to resolve potential problems of cold DM on small scales. Their impact on astrophysical objects such as
galaxies and
galaxy clusters allows for constraining the strength of this scattering and eventually further properties of the cross-section. To model self-interacting dark matter (SIDM), N-body simulations are a crucial tool widely employed by the SIDM community. In this paper, we describe the SIDM implementation in the cosmological hydrodynamical N-body code OpenGadget3 and release it to the public. It is capable of simulating elastic scattering for various differential cross-sections, including strongly anisotropic cross-sections. Beyond single-species models, the code also allows simulating a two-species model with cross-species interactions. In addition to describing the numerical schemes for modelling various flavours of SIDM, we discuss the technical challenges of implementing them. Moreover, we demonstrate through several test problems that OpenGadget3 can accurately simulate DM self-interactions. Furthermore, we assess the performance of the code and provide scaling tests. Lastly, we highlight remaining challenges in the context of SIDM and describe directions for improving the current state of the art.
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All authors Moritz S. Fischer, Marc Wiertel, Cenanda Arido, Yashraj Patil, Antonio Ragagnin, Klaus Dolag, Marcus Brüggen, Mathias Garny, Andrew Robertson, Kai Schmidt-Hoberg
Astrophysics of Galaxies
A Kiloparsec-Scale Stellar Cavity in the Center of Abell402-BCG May be Caused by Dynamic Interactions with an Ultramassive Black Hole
Michael McDonald, Gourav Khullar, David Lagattuta et al. (+18 more)
We present new observations from JWST NIRCam that reveal a striking kpc-wide cavity in the
stellar distribution of the central
galaxy in the cluster Abell402. Supporting data from HST allow us to rule out extinction due to
dust as an explanation and, instead, suggest that this is a localized depression in the
stellar density field corresponding to ~2x10^9 Msun in missing
stars within a volume of 0.5kpc^3. On larger scales, both the JWST and HST data show evidence for a 2.2kpc flattened core in the
stellar distribution (on which the smaller-scale cavity is superimposed), which implies the presence of a central ultra-massive black hole with M_BH = 6 +/- 4 x10^10 Msun. We report evidence for a mid-IR-bright point source at one edge of the cavity, suggesting that this black hole is actively accreting. MUSE spectroscopy reveal that this source is a LINER AGN and that there is a second candidate AGN on the opposite side of the cavity with a relative velocity of 370km/s – if real, this implies the presence of a kpc-separation dual AGN with a total binary mass of 6 +/- 2 x10^10 Msun, which would make this the most massive binary black hole system discovered to date. We propose that this unique
stellar cavity is the result of a short-lived dynamical interaction between at least one supermassive black hole and the background
stellar density field, caused either by three-body scattering during binary hardening or the induction of a dipole instability in the
stellar density field.
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All authors Michael McDonald, Gourav Khullar, David Lagattuta, Guillaume Mahler, Shashank Dattathri, Jose M. Diego, Alastair C. Edge, Benjamin Floyd, Michael D. Gladders, Scott A. Hughes, Mathilde Jauzac, Nader Khonji, Gavin Leroy, Richard Massey, Mireia Montes, Priyamvada Natarajan, Michael Reefe, Keren Sharon, Frank van den Bosch, Stepane Werner, Adi Zitrin
Earth and Planetary Astrophysics
A test of the Dedalus software for exoplanet atmospheric dynamics
Rick Bonhof, Quentin Changeat and James Y-K. Cho
Studying
exoplanet flow and variability requires solving atmospheric dynamics equations accurately. Here we use the shallow-water equations to evaluate and employ Dedalus3, a spectral method-based software package for solving differential equations. A well-known jet instability test is used for the evaluation; then, the package is used to investigate the nonlinear
evolution of observed, Jupiter's zonal (east–west) jets; finally, the package is used to compare hot-Jupiter flows with different initial conditions. Our results indicate that Dedalus3 can be a useful tool for investigating planetary flow dynamics, but careful testing and execution are necessary for each problem.
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Instrumentation and Methods for Astrophysics
CHRONOS Science Program
Yuki Inoue, Masashi Hazumi, Hsiang-Yu Huang et al. (+5 more)
Cryogenic sub-Hz cROss torsion-bar detector with
quantum NOn-demolition Speed meter (CHRONOS) is a proposed cryogenic torsion-bar interferometer for precision measurements in the 0.1-10 Hz band. A Sagnac speed-meter readout, power and signal recycling, and balanced homodyne detection provide control of the optical response and
quantum measurement correlations. This White Paper describes the science program, detector design, calibration, and staged experimental development. The reference sensitivity uses a multi-input
quantum model, including rear-mirror
vacuum fields and measurement-back-action correlations, combined with classical noise. Two operating points are optimized for complementary power-law-integrated sensitivity objectives. Gravitational-wave forecasts use this common noise budget and state their source and observing assumptions. The program includes intermediate-mass black-hole binaries,
stochastic backgrounds,
quantum measurement, and terrestrial
gravity perturbations. Dark-matter applications are discussed as response and feasibility studies. A differential gravitational calibrator provides a proposed Yukawa-
gravity test whose systematic floor is improved by subtracting auxiliary harmonics. These are conditional projections: experimental reach requires validation of the noise, transfer functions, environmental backgrounds, and systematic uncertainties described here.
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All authors Yuki Inoue, Masashi Hazumi, Hsiang-Yu Huang, Vivek Kumar, Ippei Obata, Mario Juvenal S Onglao III, Daiki Tanabe, Ta-Chun Yu
Astrophysics of Galaxies
Black Hole Properties of Type-1 Active Galactic Nuclei in the North Ecliptic Pole Wide Field: I. Mid-infrared Sources with Optical Counterparts
Dohyeong Kim, Myungshin Im, Hyunjin Shim et al. (+11 more)
We present measurements of black hole (BH) properties of 861 Type-1 active
galactic nuclei (AGNs) in the North Ecliptic Pole (NEP)-Wide field. These AGNs are detected in both optical and mid-infrared (MIR) surveys and are identified as Type-1 AGNs in optical spectroscopic surveys. By performing spectral energy distribution (SED) and line fitting, we obtained their MIR continuum luminosities ($L_{\rm MIR}$) as well as full width at half maximum (FWHM) values for the \ion{C}{4}, \ion{Mg}{2}, H$\beta$, and H$\alpha$ lines. Using these measurements, we derived bolometric luminosities ($10^{43.20}$–$10^{47.27}~{\rm erg~s^{-1}}$), BH masses ($10^{7.29}$–$10^{9.67}$\,$M_{\odot}$), and Eddington ratios ($10^{-2.74}$–$10^{-0.08}$) for $\sim$450 objects over a wide
redshift range ($z=0.09$–$4.71$). The use of $L_{\rm MIR}$ and FWHM values effectively alleviates the effects of
dust extinction, enabling reliable estimates of BH properties even for
dust-obscured AGNs. Moreover, we find that 34\,% of the Type-1 AGNs in the NEP-Wide field are
dust-obscured, and that their bolometric luminosities can be significantly underestimated without proper
dust extinction correction. Our relatively extinction-free BH property estimates can (i) be combined with multi-wavelength data in the NEP-Wide field to facilitate diverse studies of AGN environments, number densities, host
galaxies, and related topics, and (ii) serve as fiducial estimates for SPHEREx and other upcoming infrared (IR) spectroscopic missions covering the NEP-Wide field.
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All authors Dohyeong Kim, Myungshin Im, Hyunjin Shim, Minjin Kim, Gu Lim, Junyeong Park, Hayeong Jeong, Yongjung Kim, Yongmin Yoon, Seong Jin Kim, Yoshiki Toba, Tomotsugu Goto, Nagisa Oi, Hyunmi Song
Cosmology and Nongalactic Astrophysics
Probing Physics Beyond the Standard Model through Combined Analyses of Next-Generation Type Ia Supernova, CMB, and BAO Surveys
Srinivasan Raghunathan, Ayan Mitra, Nikolina Šarčević et al. (+11 more)
Observations of Type Ia
supernovae (\sne), which probe the late Universe, together with
baryon acoustic oscillations (BAO) and the
cosmic microwave background (CMB), which probe the intermediate and early epochs, provide complementary constraints on the expansion history of the Universe. In this work, we forecast constraints on dark energy and other extensions to the standard cosmological model by combining the SNIa sample expected from the Vera C. Rubin Observatory's Legacy Survey of Space and Time (LSST), data from current and forthcoming CMB surveys, and BAO measurements from the Dark Energy Spectroscopic Instrument (DESI). For the CMB, we use temperature, polarization, and
lensing power spectra ($TT/EE/TE/\phi\phi$) from South Pole
Telescope, the planned Advanced Simons Observatory, and a CMB-S4-like experiment. We derive constraints on $\Lambda {\rm CDM}$ and its extensions involving the dark energy equation of state parameters $(w_{0}, w_{a})$ and the sum of
neutrino masses $\sum m_{\nu}$, using a Markov Chain Monte Carlo (MCMC) sampling framework. We find that the LSST Year-3 SNIa sample can improve upon the DES Year-5 dark energy constraints by a factor of $\times2-\times2.5$, with the gains driven primarily by the significantly higher SNIa density in the LSST sample. Similarly, DESI-DR3 shows up to a $\times1.8$ improvement on dark energy parameters over DR2, driven largely by the substantial increase in low-
redshift sample. Combining CMB with LSST-Y3-SNIa and DESI-DR3-BAO yields $\sigma(w_{0}) = 0.028$ and $\sigma(w_{a}) = 0.11$ for $w_{0} w_{a} {\rm CDM}$ cosmology with the results being largely independent of the CMB
dataset. The constraints weaken by 10%-30% when freeing $\sum m_{\nu}$ and spatial
curvature. Moreover, the joint analysis of the three
datasets can enable a $2-3\sigma$ detection of $\sum m_{\nu}$.
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All authors Srinivasan Raghunathan, Ayan Mitra, Nikolina Šarčević, Fei Ge, Corentin Ravoux, Christos Georgiou, Renée Hložek, Richard Kessler, Gautham Narayan, Paul Rogozenski, Paul Shah, Georgios Valogiannis, Joaquin Vieira, the LSST Dark Energy Science Collaboration
Cosmology and Nongalactic Astrophysics
Dark Matter Recoupling
Eugenia Dallari, Francesco Castagna, Emanuele Castorina et al. (+2 more)
In the late Universe, and on cosmological scales, dark matter is conventionally assumed to be collisionless, as a consequence of the strong existing bounds on dark matter interactions at the
Cosmic Microwave Background last-scattering surface. Challenging this lore, here we show that dark matter interactions can be naturally weak at early times, but then grow to observationally relevant strengths at very late times, even significantly after reionization. This is realized if dark matter recouples to a dark radiation species in the range of
redshifts probed by the current generation of
galaxy surveys. We systematically study, for the first time, the phenomenology of this dark matter recoupling scenario. A combination of
Cosmic Microwave Background and
Baryon Acoustic Oscillation data show that the interaction needs to be weak at present, if the entirety of dark matter couples to dark radiation. From a complementary perspective, we estimate that a 4% fraction of dark matter could still be strongly interacting today. Implications for a microscopic model realizing the recoupling dynamics are discussed.
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All authors Eugenia Dallari, Francesco Castagna, Emanuele Castorina, Maria Archidiacono, Ennio Salvioni
Astrophysics of Galaxies
Far-infrared Polarization Properties of Nearby Star-forming Regions: A New Compendium of SOFIA/HAWC+ Observations
Kaitlyn Karpovich, Susan E. Clark and Enrique Lopez-Rodriguez
We present a comprehensive polarimetric study of 26 nearby molecular clouds in four far-infrared bands (53 $\mu$m~to 214~$\mu$m) using 52 archival SOFIA/HAWC+
datasets{, over half of which are unpublished}. Far-infrared
dust polarization observations probe the plane-of-sky
magnetic field. To investigate scale-dependent trends, we group the molecular clouds by distance and analyze the data at common angular ($25''$) and common physical (0.052 pc and 0.32 pc) resolutions. The two shorter wavelengths are more impacted by smoothing, exhibiting a larger decrease in percent polarization. We analyze the polarization spectrum — the polarization fraction as a function of wavelength — and find that it depends more strongly on column density than
dust temperature. We find a “falling" spectrum at the 0.052 pc resolution, but find a “flat" spectrum at the 0.32 pc resolution, suggesting that resolution plays an important role in the observed polarization spectra. We propose that warm
dust grain emission in small-scale structures ($\lesssim$~0.1 pc) traces different
magnetic field geometries only resolved in our {near} regime data. There is no preferred
magnetic field orientation across our data, which suggests that the
magnetic field in our $\sim$~parsec scale regions is decoupled from the large-scale field that is primarily parallel to the
Galactic plane. The relationship between percent polarization and column density varies between clouds, but the correlation between percent polarization and {polarization angle} dispersion is consistent across regions. This compendium highlights the value of observing at multiple far-infrared wavelengths and enables additional population-level studies of
magnetic fields and
dust across
star-forming environments.
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Instrumentation and Methods for Astrophysics
Data reduction method for OPTICAM multiband time series of transiting exoplanets
S. Páez, Y. Gómez Maqueo Chew and L. H. Hebb
We present a methodology for acquiring and reducing transiting
exoplanet light curves obtained with the OPTICAM instrument in the Observatorio Astronómico Nacional en la Sierra de San Pedro Mártir (OAN-SPM). The OPTICAM sCMOS detectors generate significant warm pixels at exposures $\geq$10s, affecting both science and calibration frames. These warm pixels are not removed by standard dark subtraction because they vary unpredictably from frame to frame. We evaluate six pre-processing methods applied to science and calibration images using the transit of TOI-7149~b observed in g$^\prime$r$^\prime$i$^\prime$. A median filter with a 3$\times$3-pixel window minimizes the effect of warm pixels without affecting
stellar signals. This median filter best reduces dispersion and red noise in the light curves when
stellar peak counts are close to the dark current level. The improvement is less significant when the
stellar peak is several thousand counts above the dark current level. We fit a multiband transit model to the light curves, measuring photometric precision, correlated noise, and retrieved planetary parameters. The transit model fitted to the light curves with pre-processing using a 3$\times$3-median filter achieves the highest
Bayesian evidence. Thus, it is our recommended method for correcting warm pixels. Finally, we present a reduction pipeline that combines Python modules (PROFE) and AstroImageJ to implement our proposed method for OAN-SPM 2.1m+OPTICAM transiting
planet observations.
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Astrophysics of Galaxies
Resolved molecular gas and star-formation in massive unquenched spirals : I. UGC 8179
Romane Cologni, Simon Flesch, Philippe Salomé et al. (+7 more)
Recent studies have uncovered a rare population of super-massive (M* > 1e11 Msun)
star-forming spiral
galaxies, Super Spiral
Galaxies (SSGs), whose existence challenges classical quenching scenarios. We investigate the resolved
star-forming and molecular-gas properties of UGC 8179 (z=0.052, log(M*/Msun)=11.62) and assess whether its local
star formation (SF) follows the same physical processes as typical
Star-Forming Main Sequence (SFMS) spirals. We combined the first NOEMA CO(1-0) interferometric observations of an SSG with pixel-by-pixel SED fitting, based on archival UV-to-mid-IR imaging. Our 3"x3" pixel maps provide resolved measurements of M*, SFR and molecular gas surface densities across its extended disc. UGC 8179 hosts a massive rotating molecular gas reservoir of M_H2 = 1.02 1e10 Msun, yielding a standard molecular gas fraction, with typical depletion time \sim 1 Gyr in the observed region, despite its extreme mass. We derived lower limits of log(fmol) > -1.61 \pm 0.06 and log(tdep) > -8.82 \pm 0.13 at the scale of the
galaxy. The large spatial extent of UGC 8179 enables us to probe low surface-density regimes hardly accessible in nearby disks (\Sigma* < 1e7 Msun / kpc2 ; \Sigma_SFR < 1e-3.5 Msun/yr/kpc2). All three resolved scaling relations (rSFMS, rKS and rMGMS) are well defined. The rKS slope (0.87 \pm 0.09) is broadly consistent with unity, indicating standard local SF processes. The rSFMS shows a shallower global slope (0.80 \pm 0.02) due to a central suppression in sSFR (~ -0.5 dex). This break suggests the influence of a bulge, driving a transition to a more dynamically regulated SF regime in the inner disc. UGC 8179 provides evidence that SSGs can sustain standard local SF processes while exhibiting central dynamical regulation at high
stellar surface densities.
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All authors Romane Cologni, Simon Flesch, Philippe Salomé, Damien Le Borgne, Médéric Boquien, Jonathan Freundlich, Pierre Guillard, Ute Lisenfeld, Francoise Combes, Laure Bouscasse
Astrophysics of Galaxies
ODIN: Spectroscopic Validation of Ly$\alpha$-Emitting Galaxy Samples with DESI
Ethan Pinarski, Govind Ramgopal, Nicole Firestone et al. (+65 more)
The One-hundred-deg^2 DECam Imaging in Narrowbands (ODIN) survey is conducting the widest-field deep narrow-band imaging of the equatorial and southern skies. ODIN uses three custom-built narrow-band (NB) filters that sample Lya-emitting
galaxies (LAEs) within thin
cosmic slices centered at z=2.4, 3.1, and 4.5. In this work, we utilize extensive DESI spectroscopy of ODIN-selected
galaxies in the COSMOS and XMM-LSS fields to validate our LAE selection. 2-4 hr exposures with DESI yielded
redshift confirmation of 3,075 ODIN LAE candidates with NB magnitudes brighter than 26~mag. Restricting to objects that yield high-confidence
redshifts, the confirmation rates are (93, 96, 92)% at z=(2.4, 3.1, 4.5). The primary contaminants consist of active
galactic nuclei at the expected Lya
redshift range and lower
redshifts (C IV, C III]), with the remainder being
star-forming
galaxies ([O II] and [O III]). We find minimal contamination from [O II] emitters in our sample (<~1%), implying that our REW>20 A narrow-band excess photometry requirement is sufficient to remove them.
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All authors Ethan Pinarski, Govind Ramgopal, Nicole Firestone, Kyoung-Soo Lee, Eric Gawiser, Arjun Dey, A. Raichoor, Francisco Valdes, Robin Ciardullo, Jessica N. Aguilar, S. Ahlen, D. Bianchi, D. Brooks, F. J. Castander, M. Candela Cerdosino, T. Claybaugh, A. Cuceu, K. S. Dawson, A. de la Macorra, P. Doel, S. Ferraro, A. Font-Ribera, J. E. Forero-Romero, E. Gaztañaga, S. Gontcho A Gontcho, Lucia Guaita, G. Gutierrez, Stephen Gwyn, H. K. Herrera-Alcantar, Ho Seong Hwang, R. Joyce, S. Juneau, R. Kehoe, D. Kirkby, T. Kisner, A. Kremin, Ankit Kumar, C. Lamman, M. Landriau, L. Le Guillou, M. E. Levi, Yufeng Luo, M. Manera, P. Martini, A. Meisner, R. Miquel, J. Moustakas, A. D. Myers, S. Nadathur, Gautam R. Nagaraj, N. Palanque-Delabrouille, Changbom Park, W. J. Percival, I. Pérez-Ràfols, F. Prada, G. Rossi, E. Sanchez, Marcin Sawicki, D. Schlegel, M. Schubnell, J. Silber, Hyunmi Song, D. Sprayberry, G. Tarlé, Paulina Troncoso Iribarren, B. A. Weaver, Yujin Yang, Ann Zabludoff
Astrophysics of Galaxies
Forward-modelling Milky Way Cepheids: selection effects and physical priors in the Gaia-HST calibration
Richard Stiskalek, Adam Riess, Harry Desmond et al. (+2 more)
The advent of high-precision
Gaia parallaxes for Milky Way Cepheids enables per cent-level calibration of the local distance ladder and the Hubble constant $H_0$. We revisit the Milky Way Cepheid calibration from
Gaia EDR3 parallaxes using a fully forward-modelled
Bayesian framework that simultaneously infers the period–luminosity relation, the
Gaia parallax zero-point offset, and individual
stellar distances while explicitly incorporating the disc geometry of the
Galaxy through the distance prior and the selection functions specified in two HST SH0ES campaigns. We derive an analytic treatment of the detection probability that accounts for magnitude, parallax, period, and extinction cuts and reduces it to a tractable integral over distance and sky position. Posterior predictive checks show that this generative model matches the observed distributions of parallaxes, magnitudes, and periods. Modelling
Galactic structure and survey truncation self-consistently in a
Bayesian framework yields period–luminosity parameters that agree with the SH0ES maximum-likelihood values at the ${<}0.5\,\sigma$ level, a consequence of the small intrinsic scatter of the Cepheid period–luminosity relation. Adopting the uniform-in-volume prior recently advocated by Högås & Mörtsell (2026), without simultaneously accounting for selection, leads to a ${\sim}\,0.05~\mathrm{mag}$ bias in the period–luminosity zero-point and posterior predictive distributions incompatible with the observed data; this shift is mostly driven by the omission of the selection model, and produces an apparent and unjustified shift in $H_0$ that reflects this mismodelling. A consistent
Bayesian treatment of
Galactic structure and selection effects reinforces the local distance-ladder determination of $H_0$, and hence the Hubble tension with early-Universe inferences.
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All authors Richard Stiskalek, Adam Riess, Harry Desmond, Guilhem Lavaux, Dan Scolnic
Astrophysics of Galaxies
The role of mass loss in constraining quenching time in dwarf galaxies from AGB and RGB star counts
Paolo Ventura, Richard D'Souza, Flavia Dell'Agli et al. (+4 more)
The capability of reconstructing the past
star formation history of
dwarf elliptical
galaxies out of the Local Volume relies on modelling bright
stellar populations currently evolving through the red
giant branch (RGB) and the asymptotic
giant branch (AGB) phases. Recent studies proposed the use of the relative fractions of RGB and AGB
stars populating specific boxes in the observational colour-magnitude plane to infer the epoch within which 90% of the
stellar population of the
galaxy formed (T90). We aim at understanding the physical process of
stellar evolution that are constrained by the relationship between the relative fraction of AGB and RGB
stars of
dwarf galaxies and the T90 epoch. We use updated
stellar models that include the description of
dust formation in the wind, to undertake a population synthesis approach, to allow monitoring the variation of the NAGB/NRGB ratio with time. The effects of some specific ingredients, such as the mass loss experienced by low-mass
stars during the RGB phase, and the details of the time variation of the
star formation rate, are extensively explored and tested against data. The mass lost by low-mass
stars during the RGB
evolution proves the most relevant ingredients affecting the time variation of NAGB/NRGB: at
metallicities ~ 1/10
solar, a mass loss ~ 0.25Msun is required to reproduce the observations. This analysis allows to derive a relationship between NAGB/NRGB and T90, with a ~ 1 Gyr uncertainty on T90.
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All authors Paolo Ventura, Richard D'Souza, Flavia Dell'Agli, Eric Bell, Claudio Gavetti, Chiara Fiumi, Marco Tailo
Solar and Stellar Astrophysics
The rotational and magnetic properties of Polaris from long-term spectropolarimetric monitoring
James A. Barron, Gregg A. Wade and Colin P. Folsom
Polaris is a highly unusual Cepheid with observed properties that are difficult to reconcile with
stellar evolutionary models. Since the initial detection of Polaris'
magnetic field in 2020, we have conducted a
magnetic monitoring campaign with the ESPaDOnS spectropolarimeter at the Canada-France-Hawaii
Telescope. We compute Stokes $V$ least-squares deconvolution profiles and measure the associated mean longitudinal
magnetic field strengths $\langle B_{z}\rangle$. The surface
magnetic field has remained remarkably stable over five years of observations, with $\langle B_{z}\rangle$ varying between approximately $-3$ G and $+0.6$ G. From the periodic modulation of $\langle B_{z}\rangle$ we infer a
stellar rotation period of $P_{\mathrm{rot}}=100.29\pm0.19$ days. This is the first direct measurement of $P_{\mathrm{rot}}$ for a classical Cepheid. Previous interferometric radius measurements and $P_{\mathrm{rot}}$ imply an equatorial rotation velocity of $v_{\mathrm{eq}}=23.3\pm0.2$ km s$^{-1}$. We set a conservative upper bound on the projected equatorial rotational velocity of $v_{\mathrm{eq}}\sin i_{\star} < 13.5$ km s$^{-1}$ and constrain the
stellar inclination angle to be $i_{\star}<37^{\circ}$. Using the previously determined orbital solution, we find a high likelihood of a strong
spin-orbit misalignment. We determine the lower bound on the obliquity angle between the
stellar rotation and orbital axes to be $\beta>18.7^{\circ}$ at 99% confidence. We discuss the challenges in interpreting the origin and properties of the surface
magnetic field in the context of Polaris' uncertain evolutionary history and the merger hypothesis.
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Astrophysics of Galaxies
A Modified Conveyor Belt Model: Implications for Surface Density Thresholds for Massive Star Formation
Nicholas Larose, C. R. Kerton, Kathryn Devine et al. (+1 more)
Recent models and simulations of cluster formation within molecular clumps consider multi-scale, hierarchical
accretion, which leads to clump mass growth over time. This mode of mass accumulation could have implications regarding the
evolution of observable properties such as mass and radius, bringing into question the interpretation of commonly cited thresholds for high-mass
star formation. In this paper, we use the conveyor belt model of cluster formation to create synthetic cores/clumps and derive physical and observational properties. We show that while this model successfully predicts many observed trends, modifications are required to match properties of high-mass prestellar clumps. When the model clumps are observationally classified as intermediate- or high-mass
star-forming, the threshold delineating these two groups agrees with those found in the literature; however, results show that high-mass clumps at early evolutionary stages can be misclassified using standard surface density thresholds. Our logistic regression analysis reveals the quantity of material to ever enter a
star-forming region is the most important factor in differentiating intermediate- and high-mass
star-forming regions. This implies observations characterising the environment surrounding
star-forming regions are crucial, especially at early evolutionary stages.
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All authors Nicholas Larose, C. R. Kerton, Kathryn Devine, Grace Wolf-Chase
Astrophysics of Galaxies
The emerging timescale of young star clusters regulated by cluster stellar mass
Alex Pedrini, Angela Adamo, Daniela Calzetti et al. (+23 more)
Quantifying the timescales of
star cluster emergence from their natal clouds remains one of the main challenges in understanding the
star formation process. These timescales are fundamental measurements of the
star formation cycle within
galaxies, yet are difficult to constrain due to the complex interplay between
stellar feedback and
star formation across multiple physical scales. Here we present Hubble Space
Telescope and James Webb Space
Telescope observations of thousands of young
star clusters in four nearby
galaxies (M51, M83, NGC 628 and NGC 4449). A substantial fraction of these clusters are still embedded within their natal gas and remain invisible at optical wavelengths. We constrain their emergence process by measuring the timescales required to disperse the surrounding material. We find a strong correlation between dispersal timescale and cluster
stellar mass, with massive clusters emerging faster than their lower-mass counterparts. This is a critical constraint on
star formation and
stellar feedback simulations, which struggle to fully reproduce
star clusters formation and emergence. Our results emphasize the central role of massive clusters in driving the escape of ionizing radiation into the
galactic medium. Finally, they impose time limitations for
planet formation in massive cluster environments where disks get exposed to ultraviolet irradiation and further gas infall is halted.
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All authors Alex Pedrini, Angela Adamo, Daniela Calzetti, Arjan Bik, Thomas J. Haworth, Bruce G. Elmegreen, Mark R. Krumholz, Sean T. Linden, Benjamin Gregg, Helena Faustino Vieira, Varun Bajaj, Jenna E. Ryon, Ahmad A. Ali, Eric P. Andersson, Giacomo Bortolini, Michele Cignoni, Ana Duarte-Cabral, Kathryn Grasha, Natalia Lahén, Thomas S.-Y. Lai, Drew Lapeer, Matteo Messa, Göran Östlin, Elena Sabbi, Linda J. Smith, Monica Tosi
Astrophysics of Galaxies
FEAST: a NIRSpec/MOS survey of emerging young star clusters in NGC 628
Helena Faustino Vieira, Angela Adamo, Neville Shane et al. (+18 more)
JWST can pierce through dusty molecular clouds to study the early stages of
star formation, where young
star clusters are actively driving
stellar feedback and still emerging from their natal cloud. We present a first look of the JWST/NIRSpec multiplex spectroscopy observations acquired by the Feedback in Emerging extrAgalactic
Star clusTers (FEAST) program for the nearby spiral
galaxy NGC628. We showcase JWST's ability to resolve the spectral properties of emerging young
star clusters (eYSCs) and their immediate interstellar medium (ISM) by focusing on a bright
star-forming complex ($0.5\times0.5~\mathrm{kpc}^2$) in the northern spiral arm as a science proof-of-concept. The eYSC spectra are rich in ionized gas (from HII regions), as well as warm H$_2$ and polycyclic aromatic hydrocarbon (PAH) emission from photodissociation regions (PDRs), consistent with young
star formation. $\mathrm{Pa}\alpha$ equivalent widths and H/He ionizing
photon fluxes both indicate the presence of hot, young massive
stars (O8.5V-O8V), consistent with photometry SED estimates. The ionized gas is highly correlated with H$_2$ and PAH emission, suggesting that the PDR morphology evolves as clusters emerge from their natal cloud. We find a photoionization-dominated regime from independent line diagnostics, with little contribution from
Supernovae-driven shocks, highlighting the importance of pre-
Supernovae feedback when massive
stars are present. This pilot study showcases how JWST's multiplex spectroscopy mode can disentangle the mechanisms present in the youngest stages of
star formation for the first time outside the Local Group.
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All authors Helena Faustino Vieira, Angela Adamo, Neville Shane, Linda J. Smith, Arjan Bik, Thomas S.-Y. Lai, Alex Pedrini, Leslie K. Hunt, Sean T. Linden, Giacomo Bortolini, Anne S. Buckner, Daniela Calzetti, Matteo Correnti, Ana Duarte-Cabral, Kathryn Grasha, Kelsey E. Johnson, Drew Lapeer, Matteo Messa, Göran Östlin, Linn Roos, Elena Sabbi
Solar and Stellar Astrophysics
Multi-spacecraft constraints on relativistic solar energetic particle transport in the widespread 28 October 2021 event
E. Lavasa, J. T. Lang, A. Papaioannou et al. (+6 more)
Aims. We investigated the transport of
solar energetic particles (SEPs) during the relativistic widespread event of 28 October 2021, quantifying the role of parallel and perpendicular
diffusion and constraining the spatial extent of the injection region. Methods. We employed inverse modeling of particle focused transport and 2D numerical simulations including cross-field
diffusion. Multi-spacecraft observations from STEREO-A,
Solar Orbiter, and near-Earth spacecraft are used to reproduce particle intensity profiles and anisotropies across a wide range of electron and
proton energies. Simulated flux profiles are compared across different heliolongitudes to derive consistent transport parameters. Results. The analysis yields parallel mean free paths within or slightly above the Palmer consensus range, and perpendicular mean free paths that correspond to $\sim 1$–$3\%$ of parallel for electrons and $\sim 5$–$10\%$ for
protons. The injection region is found to be relatively narrow ($\leq 20^\circ$), and decreasing with particle
rigidity. Multipoint simulations indicate that the observed flux and anisotropy profiles can only be reproduced by a narrow injection region and significant cross-field
diffusion. Electron and
proton release times align well with the parent X1.0
flare and associated coronal mass injection (CME) onset, indicating that a compact acceleration region coupled with efficient interplanetary
diffusion governed the event's broad spatial extent.
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All authors E. Lavasa, J. T. Lang, A. Papaioannou, R. D. Strauss, S. A. Mallios, A. Hillaris, A. Kouloumvakos, A. Anastasiadis, I. A. Daglis
Astrophysics of Galaxies
Going Wide and Deep with Roman: The z~6-9 UV luminosity function in a Roman Deep Field
Micaela B. Bagley, Steven L. Finkelstein, James Rhoads et al. (+4 more)
We present a trade study of possible ultra-deep surveys with the Nancy Grace Roman Space
Telescope, optimizing the depth-area-filter parameter space for high-
redshift galaxy science. Using a mock
galaxy catalog derived from a 2 sq. degree lightcone created using the Santa Cruz semi-analytic model and populated with over 7.6 million
galaxies at 0<z<10 with M_UV < -15, with realistic clustering and synthetic photometry, we evaluate sixteen 500-hour survey configurations spanning 0.28-2 sq. degrees and four filter combinations. We demonstrate that even a single Roman pointing dramatically reduces
cosmic variance compared to HST-like observations, more faithfully recovering the true UV luminosity function. For each survey configuration, we explore photometric
redshift recovery, sample contamination, and measurements of the rest-UV luminosity function and non-ionizing UV luminosity density across four
redshift bins at z~6-9. We find that inclusion of the R062 filter is essential for studies at z~5-6, reducing sample contamination from nearly 100% to negligible levels and recovering the bright end of the luminosity function. The F184 filter improves
galaxy recovery at z>9 and is critical for
stellar contamination removal at all
redshifts. Based on these results, we recommend that a Roman ultra-deep survey cover at least two Roman pointings (0.56 sq. degrees) with all six filters (R062, Z087, Y106, J129, H158, F184), reducing uncertainties on the rest-UV luminosity density by factors of 2-4 relative to the deepest existing JWST programs. Building off of the Deep Tier of the High Latitude Time Domain Survey to add depth and filter coverage to existing (or planned) observations is an excellent option.
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All authors Micaela B. Bagley, Steven L. Finkelstein, James Rhoads, Sangeeta Malhotra, L. Y. Aaron Yung, Rachel S. Somerville, Casey Papovich
Cosmology and Nongalactic Astrophysics · Cross-listed from gr-qc
Cosmological Spacetimes with Sign-Changing Spatial Curvature and Topological Transitions
Gerardo García-Moreno, Bert Janssen, Alejandro Jiménez Cano et al. (+3 more)
Observational evidence, together with practical computations and modeling, supports a Euclidean spatial sector in the current cosmological model based on the FLRW metric. This, however, would imply that the total amount of matter and energy immediately after the Big Bang must have been infinite, an implication that could only be avoided through a transition from a closed to an open universe, a process forbidden in standard FLRW models. In this article, we investigate the spacetimes resulting from promoting the spatial
curvature $k$ in FLRW spacetimes to a time-dependent function, $k \to k(t)$, allowing it to change sign and thereby allowing changes in the
topology of the constant-$t$ slices. Although previously dismissed due to a classical
theorem by Geroch, such transitions are shown to be consistent with global hyperbolicity when the comoving time is distinct from a Cauchy time, as recent work by one of the authors demonstrates. We construct three distinct geometries exhibiting this behavior using different representations of constant-
curvature spaces. We analyze their global properties and identify mild conditions under which they remain globally
hyperbolic. Furthermore, we characterize their Killing vectors, proving a general result for spherically symmetric spacetimes and compare them with known geometries in the literature.
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All authors Gerardo García-Moreno, Bert Janssen, Alejandro Jiménez Cano, Marc Mars, Miguel Sánchez, Raül Vera
High Energy Astrophysical Phenomena
Chinami Kato, Hiroki Nagakura, Akira Ito et al. (+4 more)
We present the first systematic study of
neutrino emissions from massive
stars, continuously tracking the late evolutionary stages through the early core-collapse
supernova phase. Using progenitor and
supernova models, we analyze the
neutrino luminosities and spectra for progenitors with initial masses of 10–40~$M_\odot$. Our systematic analysis reveals that the compactness parameter ($\xi_{2.5}$) and carbon-oxygen core mass ($M_{\text{CO}}$) exhibit strong correlations with
neutrino emission. In the pre-
supernova phase, the time-integrated number of
neutrinos correlates with $\xi_{2.5}$ when integrated over the final day and with $M_{\text{CO}}$ for longer durations. For the early
supernova phase ($<200$ ms post-bounce), the
neutrino properties are relatively insensitive to the specific
stellar evolution code used, allowing for a reliable extraction of physical correlations. We confirm that the
neutrino emission features, including the electron
neutrino burst properties and
accretion-powered luminosity of other species, reflect the progenitor's compactness. An evaluation of the observational feasibility for a nearby progenitor using a False Alarm Rate approach suggests that these correlations can persist even under practical detection conditions. Such a joint analysis of both phases provides complementary constraints on the internal structure. All calculated time-series data will be made publicly available.
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All authors Chinami Kato, Hiroki Nagakura, Akira Ito, Ryosuke Hirai, Shun Furusawa, Takashi Yoshida, Ryuichiro Akaho
Astrophysics of Galaxies
POLAR-II: modeling star formation history of galaxies on the 21-cm signal from Epoch of Reionization
Qing-Bo Ma, Raghunath Ghara, Benedetta Ciardi et al. (+6 more)
Galaxies may suffer some starburst and quenched periods in their history due to e.g.
galaxy mergers and feedback. However, semi-numerical simulations of the Epoch of Reionization (EoR) typically do not accurately model the effects of the
star formation history (SFH) of
galaxies. Keeping the same total ionizing
photon budget from
galaxies, we investigate how the ionization and heating of the Intergalactic Medium (IGM), as well as the associated 21-cm signal during the EoR, depends on the variations in the modeling of the SFH of
galaxies. We adopt the Jiutian-300 N-body dark matter simulation and the semi-analytic model L-
Galaxies 2020 to model
galaxy formation. Using the
galaxy catalog from L-
Galaxies 2020 as input, we post-process the Jiutian-300 density field with the one-dimensional radiative transfer code Grizzly to model the reionization process and the 21-cm signal. We find that the ionized regions produced by
galaxies with a SFH derived from L-
Galaxies 2020 are slightly larger and warmer than the ones obtained with a constant SFR. For a fixed
stellar mass,
galaxies produce smaller ionized regions with increasing
stellar mass weighted
stellar age $\tau_{\rm age}$. This results in a different
topology and timing of the IGM ionization and heating obtained from Grizzly. The SFH of
galaxies is highly dependent on $\tau_{\rm age}$ and
redshift. Different models of the
galactic SFH affect the gas heating and ionizing processes during the EoR, and as a consequence also the 21-cm global signal and power spectrum.
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All authors Qing-Bo Ma, Raghunath Ghara, Benedetta Ciardi, Anshuman Acharya, Bin Yue, Ilian T. Iliev, Léon V. E. Koopmans, Garrelt Mellema, Saleem Zaroubi
High Energy Astrophysical Phenomena
Joint Bayesian Source and Lens Reconstruction for Multi-messenger Binary Black Holes
Laura Uronen, Tian Li, Justin Janquart et al. (+5 more)
If a gravitational wave event is lensed by a cluster or
galaxy in our line-of-sight, it is expected that its host
galaxy would also be lensed. Therefore, connecting lensed gravitational wave events even without direct optical counterpart could be feasible by identifying matching lenses in electromagnetic data and surveys. Seminal work has demonstrated the potential of this approach in LVK, Euclid, HST, JWST, and CSST mock data, motivating the need for a dedicated software package to perform such analyses in practice. Here, we present the alpha-version of silmarel, the first software package designed to bridge these
cosmic signals and enable us analysis of real LVK gravitational-wave binaries together with
telescope observations from instruments like Euclid or Hubble Space
Telescope, and the future of multimessenger binary black hole
lensing.
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All authors Laura Uronen, Tian Li, Justin Janquart, Hemanta Phurailatpam, Jason Poon, Thomas Collett, Leon Koopmans, Otto Hannuksela
Solar and Stellar Astrophysics
Understanding the impact of binary mass transfer in the accretor's measurable parameters
Magdalena Vilaxa-Campos, Nathan Leigh and Taeho Ryu
Binaries and higher order systems can experience mass transfer events between their components. The angular momentum carried by the gained mass can change the observable parameters of the accretor and
spin it up to critical rotation. In this work, we aim to explore the
spin-up effect of direct
accretion through a stream as a possible mechanism for an accretor to gain more than a tenth of its initial mass without acquiring enough momentum to reach critical rotation. We present a novel analytical model to characterize the effects of direct mass transfer on the accretor's measurable parameters as a function of the binary's semi-major axis and eccentricity and the donor's rotation velocity. This model takes a two-body approach to the problem, where a stream is decomposed as many discrete particles that do not interact with each other and are influenced by the accretor's gravitational potential only. Each parcel has an instant orbital solution derived from its initial conditions. The contribution each accreted parcel has to the total
spin-up of the accretor is given by its tangential velocity at impact, through conservation of angular momentum. Direct mass transfer proves to be inefficient at spinning up the accretor and thus enables the
star to gain a great fraction of its initial mass without reaching critical rotation. We also quantify the fraction of mass that directly impacts the accretor in contrast to the mass that is either lost from the system or creates a disk around a
star. Our results show that systems are the most mass-conservative when the orbit is tighter or when the donor's
spin is greater. In terms of eccentricity, the conservation of mass shows mixed results depending on the system's other initial properties. However, systems with higher eccentricity are consistently a hundred percent conservative within our parameter space.
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Instrumentation and Methods for Astrophysics
Supernova scores for active anomaly detection
Semenikhin T. A., Kornilov M. V., Pruzhinskaya M. V. et al. (+3 more)
Large time-domain sky surveys generate extensive multi-year catalogs of light curves in which scientifically valuable transients, such as
supernovae (SNe), are vastly outnumbered by artifacts and routine
star variability. While supervised machine learning models can efficiently filter known classes, they struggle with extreme class imbalance and may overlook rare or novel events. Conversely, unsupervised anomaly detection provides broad discovery potential but lacks targeted sensitivity. We present a hybrid strategy that integrates a supervised SN probability score (SN-score) into the PineForest active anomaly detection framework to enhance SN discovery rate in the 23rd data release of the Zwicky Transient Facility. We train a binary classifier using light-curve features of spectroscopically confirmed SNe from the ZTF Bright Transient Survey, achieving a ROC-AUC approximately 0.98. Incorporating the SN-score as an additional feature, together with a small set of labeled priors, significantly accelerates the discovery of SN-like transients across ten extragalactic ZTF fields. This method increases discovery efficiency without compromising the ability to identify diverse astrophysical anomalies. Application of the combined methodology resulted in the discovery of seven previously unreported SN candidates, one AGN candidate, one unusual
Galactic variable
star SNAD283, as well as two host
galaxies exhibiting multiple
supernova events. These results demonstrate its value for scalable and expert-guided transient search in current and future surveys, including the Vera C. Rubin Observatory Legacy Survey of Space and Time.
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All authors Semenikhin T. A., Kornilov M. V., Pruzhinskaya M. V., Krushinsky V. V., Malanchev K. L., Dodin A. V
Earth and Planetary Astrophysics
Shaken, not stirred: inefficient mixing of CM- and CI-like materials
Sarah E. Anderson, Pierre Vernazza and Miroslav Broz
A recent study suggests that CM chondrite-like planetesimals formed in the vicinity of Saturn, in a pressure bump outside the gap carved by proto-Jupiter. While a fraction of these objects was implanted into the asteroid belt as a consequence of Saturn's growth, it remains unclear whether the scattered remainder could reach the ice-
giant region and mix with more distant carbonaceous reservoirs. We test whether outward scattering during Saturn's growth and migration can implant CM-like bodies onto long-lived orbits in the Uranus-Neptune region, where they could contaminate the CI reservoir. We performed N-body integrations of 100 km planetesimals launched from the outer edge of Jupiter's gap, including gas drag and the gravitational perturbations of growing Jupiter and Saturn, with optional inclusion of a nearby ice-
giant embryo. We explored a range of gas surface-density profiles and growth timescales. While Saturn's growth efficiently scatters CM-like planetesimals, fewer than about 2 percent are implanted beyond 15 au, even under gas-rich conditions, because gas drag damps their eccentricities and drives them back toward their perihelia rather than allowing them to circularize at larger distances. Adding an ice-
giant core modestly increases the outward reach (up to about 4 percent in the most gas-rich case), but Type-I migration further lowers perihelia, making long-term retention at large distances difficult. For a CM mass budget M_CM,tot about 1 M_Earth, this implies at most M_CM < 0.02-0.04 M_Earth reaches 15-25 au, corresponding to a diluted mass fraction < (1-2) x 10^-3 in the outer ring, hence negligible contamination of the CI reservoir. Combined with the distinct radial distributions of CM- and CI-like asteroids in the belt, these results imply limited mixing of carbonaceous reservoirs and isolation of the CI reservoir.
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Astrophysics of Galaxies
ODIN: Confirmation and 3D Reconstruction of Six Massive Protoclusters at Cosmic Noon
Ashley Ortiz, Vandana Ramakrishnan, Kyoung-Soo Lee et al. (+64 more)
Protoclusters represent sites of accelerated
galaxy formation and extreme astrophysical activity characteristic of dense environments. Identifying massive protoclusters and mapping their spatial structures are therefore crucial first steps in understanding how the large-scale environment influences
galaxy evolution. We combine wide-field Ly$\alpha$ imaging from the ODIN survey with extensive DESI and ancillary spectroscopy across the extended COSMOS and XMM-LSS fields ($\approx$14 deg$^2$) to search for massive protoclusters. We confirm six systems at $z\approx 2.4$ and $z\approx 3.1$, reconstruct their three-dimensional structures, estimate descendant
halo masses, and, for one structure at $z\approx 3.12$, demonstrate that overlapping narrowband filters ($NB497$ and $N501$) provide accurate
redshift tomography for emission-line
galaxies. One protocluster at $z\approx 2.45$ overlaps with one of the LATIS tomographic fields, enabling direct comparison between
galaxy and H i overdensities traced by Ly$\alpha$ forest absorption. Another at $z\approx 3.12$ hosts a massive quiescent
galaxy ($M_{\ast} \approx 1.2 \times 10^{11}M_\odot$), indicating early quenching in a dense environment. By comparing Ly$\alpha$ emission properties across environments, we find that protocluster
galaxies exhibit higher median line fluxes and a deficit of faint emitters relative to the field. The effect is strongest when both 2D and 3D density information are combined, indicating that
galaxies in the densest protocluster cores are most affected by environmental processes. This effect is stronger at $z\approx3.1$ than at $z\approx2.4$, suggesting possible
redshift evolution.
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All authors Ashley Ortiz, Vandana Ramakrishnan, Kyoung-Soo Lee, Arjun Dey, Yucheng Guo, Ethan Pinarski, Anand Raichoor, Francisco Valdes, J. Aguilar, Steven Ahlen, Maria Celeste Artale, Davide Bianchi, August Bliese, David Brooks, Rebecca Canning, Maria Cerdosino, Todd Claybaugh, Andrei Cuceu, Axel de la Macorra, Peter Doel, Jaime Forero, Eric Gawiser, Enrique Gaztanaga, Satya Gontcho, Caryl Gronwall, Lucia Guaita, Gaston Gutierrez, Hiram K. Herrera-Alcantar, Ho Seong Hwang, Woong-Seob Jeong, Dick Joyce, Robert Kehoe, Theodore Kisner, Anthony Kremin, Ankit Kumar, Ofer Lahav, Martin Landriau, Jaehyun Lee, Seong-Kook Lee, Laurent Le Guillou, Marc Manera, Aaron Meisner, Ramon Miquel, Byeongha Moon, John Moustakas, Adam Myers, Seshadri Nadathur, Nathalie Palanque-Delabrouille, Changbom Park, Will Percival, Ignasi Perez-Rafols, Francisco Prada, Eshwar Puvvada, Graziano Rossi, Eusebio Sanchez, David Schlegel, Michael Schubnell, Joseph Harry Silber, Hyunmi Song, David Sprayberry, Gregory Tarle, Paulina Troncoso, Ana Sofia Uzsoy, Benjamin Weaver, Yujin Yang, Rongpu Zhou, Hu Zou
High Energy Astrophysical Phenomena
Fast X-ray Transients produced by Off-axis Jet-Cocoons from Long Gamma-Ray Bursts
Jian-He Zheng and Wenbin Lu
Fast X-ray transients (FXTs) have been detected for over a decade, yet their origins are still enigmatic. The observed association between FXTs and broad-lined Type Ic
supernovae (SNe Ic-BL) suggests that some may share the same progenitor with Long Gamma-Ray Bursts. In this work, we numerically simulate the long-term
evolution of a relativistic jet propagating from inside the progenitor
star up to the
photon diffusion radius of the cocoon. Then we post-process the hydrodynamic results and calculate the cocoon cooling emission for various viewing angles from the jet axis. We find that, for viewing angles $\theta_{\rm v}=10^{\circ}$-$20^{\circ}$, the off-axis cocoon emission can produce FXTs with luminosity $L_{\rm X}\simeq 10^{47-48} {\rm\, erg\,s^{-1}}$ and duration $t_{\rm X}\simeq 10$-$100\,$s. The observed spectra are quasi-thermal with the peak energy $E_{\rm peak}\simeq0.8$ keV. These properties naturally explain observational features of { a fraction of FXTs}, including their high luminosity, soft spectra, and lack of gamma-ray counterparts. The Rayleigh-Jeans tail of the FXT spectra extends to the UV, producing an early UV flash simultaneously. As the cocoon expands and cools, the emission peak shifts to UV and optical bands, resulting in a bright optical plateau lasting for $\sim1$ day with color temperature $T_{\rm UV/opt} \simeq (1{-}3)\times10^{4}\,$K and bolometric luminosity $L_{\rm bol}\simeq10^{41-42} {\rm\, erg\,s^{-1}}$, before the emergence of
supernova emission. Although our model underpredicts the UV/optical luminosity at $\sim1$ day for some events (e.g. EP 240414a), it still provides useful diagnostics for identifying the origins of FXTs.
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