Recently, several long-duration gamma-ray bursts (GRBs) associated with kilonovae have cast doubt on the traditional, dichotomous mapping between gamma-ray duration and progenitor system. Here, we investigate the rates and properties of bursts which appear to cross this dichotomy using a sample of GRBs for which progenitor constraints are possible. We first build a sample of known Swift-detected GRBs at z<0.3, finding 8 short- and 21 long-duration GRBs. Of these long GRBs, we find 9 bursts with deep limits on supernova emission, evidence for kilonova emission, or association with a quiescent galaxy (31

Two time domain surveys, recently funded as part of the Eric and Wendy Schmidt Observatory System: the Argus Array, in the optical, and the Deep Synoptic Array (DSA), in the radio, will transform gamma-ray burst (GRB) science via the serendipitous discovery of hundreds of GRB afterglows per year. In this work, we simulate DSA and Argus observations of GRB afterglows. We find that, of the long-duration GRBs (LGRBs) detected by the Fermi Gamma-ray Burst Monitor, (26 ± 3)% will yield afterglow detections with Argus and (44 ± 3)% with DSA, corresponding to rates of 51 ± 5 and 86 ± 8 per year, respectively. We also compute rates for both upcoming and proposed GRB monitors: the forthcoming StarBurst Multimessenger Pioneer, with 84 ± 6 detections per year in Argus and 158 ± 11 detections per year in DSA, and the Moon Burst Energetics All-sky Monitor (MoonBEAM) concept, with 90 ± 9 per year in Argus and 160 ± 14 per year in DSA. The observatory system will also detect 118 ± 10 optical and 199 ± 17 radio afterglows per year, independent of GRB triggers, exceeding the current annual rate with global follow-up. Afterglow counterparts to short-duration GRBs, originating from neutron star mergers, will be detected at 5%–10% of the LGRB afterglow rate, which is promising for multimessenger detections of gravitational wave sources and constraining the neutron star merger rate. The Argus Array, with its second–minute cadence, will detect afterglows before they peak ∼18% of the time, which will dramatically increase the sample of observed reverse shock and prompt optical emission.

Gamma-Ray Bursts (GRBs) are the most luminous explosions in the universe, and are of great interest in astrophysics research. Despite the development of onboard trigger algorithms, significant obstacles remain in identifying weak events and effectively filtering out false detections. These challenges motivate the exploration of innovative technologies such as deep learning and quantum computing to help traditional triggers as a second verification level and increase reliability across the detection pipeline. We present a comparison of a classical and a quantum autoencoder running on simulated quantum hardware, tackling an anomaly detection task in a controlled environment. The goal is to compare their performance, with a focus on resource-constrained scenarios involving limited data and trainable parameters. Both approaches were tested using a simulated set of light curves from the anticoincidence shield of the Compton Spectrometer and Imager (COSI) soft gamma-ray telescope. Short-duration GRB signals were simulated using MEGAlib and then modified through data augmentation techniques. The results indicate that while classical autoencoders reconstruct better, achieving a Mean Squared Error (MSE) as low as 2.97 & times; 10-5, the efficiency of the quantum autoencoders is notable with lower numbers of parameters and smaller datasets. Using only 10 trainable parameters and 100 input samples, the quantum model obtained an MSE of 2.24 & times; 10-4, outperforming its classical counterpart (MSE of 3.81 & times; 10-2 with 705 parameters). These results show a promising role for quantum machine learning in astrophysical contexts where data related to GRBs are limited or lightweight model architectures are essential.

The discovery of delayed GeV emission from the extragalactic magnetar giant flare (MGF) GRB 200415A, located in the nearby Sculptor galaxy, revealed for the first time that these rare transients can launch relativistic outflows that power high-energy afterglows. Motivated by the recent identification of additional nearby MGF candidates in the archival data of the Fermi Gamma-ray Burst Monitor, we conduct a search for GeV counterparts with the Fermi Large Area Telescope (LAT). We analysed post-trigger time intervals taken in the range 10^2–10^4 s using a maximum-likelihood approach and performed a stacking analysis of all candidates with LAT coverage. In addition, we searched for photon triplets through a waiting time analysis to identify events potentially associated with MGFs. We recover the known delayed signal from GRB 200415A but find no GeV emission from the remaining six candidates. For three events, the earliest emission is unconstrained because the 10^2 s interval contains zero exposure after standard selections. For the events with LAT coverage, we obtain upper limits at 95% confidence level of order F_E ∼ 10^-9 erg cm^-2 s^-1 for the individual events, and a stacked population-averaged limit of ≈2×10^-10 erg cm^-2 s^-1. We interpret these upper limits within the relativistic fireball framework, where the prompt spectral peaks favor a baryonic-poor regime (η> η_*). For the candidates with hard prompt spectrum and early LAT coverage, the baryonic-poor condition restricts the mass of relativistic ejecta to M_b ≲ 1–4 × 10^22 g; the LAT upper limits confirm that the predicted GeV afterglow from such clean outflows falls below current instrumental sensitivity.

The Habitable Worlds Observatory (HWO) is a future NASA flagship mission concept identified by the Astro2020 Decadal Survey as the highest priority for large space missions. HWO should conduct "transformative astrophysics" and search for biosignatures in the atmospheres of approximately 25 potentially Earth-like planets. To further the early-stage development of HWO, NASA formed the Science, Technology, Architecture Review Team (START). In turn, START invited the scientific community to join working groups to explore the potential discovery space. In this paper, we present 70 science cases that resulted from this process. The cases address four scientific pillars: growth of galaxies (15 cases), evolution of the elements (13 cases), solar systems in context (32 cases), and living worlds (10 cases). Combined, they would address 27 of the 30 science questions and discovery areas identified by Astro2020. The 140 observing programs needed for the 70 investigations encompass a rich variety of spectroscopic (for 87

Gamma-ray bursts (GRBs) are the most energetic bursts of light in our universe, and rapid progenitor association of these events can lead to targeted and optimized follow-up observations, ultimately providing better insights about the physics involved. In this note, we investigate a semi-supervised machine learning algorithm, that utilizes label propagation, as a classification method. Using a dataset of 2512 GRBs we evaluate the method's ability to assign probabilistic class memberships based on a subset of events with known progenitors. Further analysis is ongoing to improve the method and future progress will be made to refine the classification algorithm and the dataset.

Time-Domain and Multi-Messenger Astrophysics (TDAMM) is entering a new era in which the rate and diversity of transient discoveries will grow rapidly across electromagnetic, gravitational-wave, neutrino, and cosmic-ray facilities. The scientific return from these investments will increasingly depend not on discovery alone, but on the ability to identify, prioritize, and coordinate follow-up observations across a heterogeneous and globally distributed network of observatories. This white paper summarizes the outcomes of the Fourth TDAMM Workshop and assesses the near-term discovery landscape, the infrastructure and tools that support coordinated observations, and the technical, policy, and capability gaps that may limit future progress. The workshop identified three principal challenges: insufficiently scalable and interoperable alert and coordination infrastructure, policies that impede rapid multi-facility observations and rare-event science, and the potential loss of critical high-energy, rapid-response, and spectroscopic capabilities. The white paper identifies the need for sustained support for alert distribution, brokers, standardized observatory metadata, cross-facility coordination platforms, and unified follow-up repositories; expanded joint observing opportunities and funding mechanisms for coordinated analysis; and strategic investment in future TDAMM facilities. The white paper also present a framework for community observing plans that would establish pre-coordinated responses to rare, high-impact events, supported by transparent governance, immediate public data release, and regular community revision. Science overviews and detailed observing strategies are provided for gamma-ray bursts, tidal disruption events, X-ray binaries, novae, supernovae, magnetars, compact binary mergers, and high-energy neutrino sources.

The Fermi Gamma-ray Burst Monitor (GBM) has been in operation for over 17 years, during which it has observed more than a thousand bursts from soft gamma repeaters (SGRs), also known as magnetars. Serving as a laboratory for extreme physics, magnetars are a sub-family of neutron stars characterized by extreme magnetic field strength, observed through a combination of persistent and short transient emission across the electromagnetic spectrum. We present the comprehensive GBM catalog of SGR short bursts which supersedes the 5-year catalog of Collazzi et al. 2015. The new catalog contains 1254 SGR short bursts observed over 17 years, providing the longest uninterrupted, high-sensitivity all-sky monitoring of magnetar bursts with unprecedented spectral and temporal resolution. Our catalog contains bursts from 17 unique Galactic sources, with major contributions by bursts from SGR J1935+2154 and SGR J1550-5418. We present overall characteristics of these bursts, such as the durations, spectral parameters for various photon models, fluxes, as well as their comparison with recently published catalogs of other missions and the previous GBM magnetar catalog. The machine readable catalog, as well as burst spectra and response files are made publicly available for the community.

We present follow-up observations of the day-long, repeating gamma-ray burst (GRB) GRB 250702B with the Near Infrared Spectrograph on board the James Webb Space Telescope. Through the identification of narrow hydrogen emission lines at a consistent redshift of z = 1.036 ± 0.004, we calibrate the distance scale, and therefore the energetics, of this unique extragalactic transient. At this distance, the resulting γ -ray energy release is at least E _γ _,iso = 2.2 × 10 ^54 erg. We find no evidence for ongoing transient emission at the GRB position and exclude any accompanying supernova (SN) with a luminosity comparable to the Type Ic broad-line SN 2023lcr, though we are unable to rule out a fainter SN counterpart owing to high extinction. The inferred rate of such events, assuming at most one in the lifetime of Fermi, suggests that such bursts are very rare, with volumetric rates over 1000 times lower than normal high-luminosity long GRBs and >10 ^5 times lower than core-collapse SNe, when corrected for beaming. Furthermore, we find that the host galaxy is unique among GRB host galaxies and extremely rare in the general galaxy population, being extremely large and dusty and with high stellar mass. The identification of such an exotic GRB in such an unusual galaxy raises the possibility that the environment was important in the progenitor channel creating GRB 250702B.

The General Coordinates Network (GCN) is NASA’s time-domain and multimessenger alert system. GCN distributes two data products: automated “Notices” and human-generated “Circulars” that report the observations of high-energy and multimessenger astronomical transients. The flexible and nonstructured format of GCN Circulars, comprising more than 40,500 Circulars accumulated over three decades, makes it challenging to manually extract observational information, such as redshift or observed wave bands. In this work, we employ large language models (LLMs) to facilitate the automated parsing of transient reports. We develop a neural topic modeling pipeline with open-source tools for the automatic clustering and summarization of astrophysical topics in the Circulars archive. Using neural topic modeling and contrastive fine-tuning, we classify Circulars based on their observation wave bands and messengers. Additionally, we separate gravitational-wave event clusters and their electromagnetic counterparts from the Circulars archive. Finally, using the open-source Mistral model, we implement a system to automatically extract gamma-ray burst (GRB) redshift information from the Circulars archive, without the need for any training. Evaluation against the manually curated Neil Gehrels Swift Observatory GRB table shows that our simple system, with the help of prompt-tuning, output parsing, and retrieval augmented generation (RAG), can achieve an accuracy of 97.2% for redshift-containing Circulars. Our neural search-enhanced RAG pipeline accurately retrieved 96.8% of redshift Circulars from the manually curated archive. Our study demonstrates the potential of LLMs to automate and enhance astronomical text mining and provides a foundational work for future advances in transient alert analysis.

Astrophysical observations of our universe have been key to our understanding of how the universe works. Shortly after the turn of the millennium, the National Research Council delivered Connecting Quarks with the Cosmos: Eleven Science Questions for the New Century. In the subsequent quarter-century, we have made substantial progress in answering each question. These advancements have, in part, arisen because of the success of major US facilities across several domains of physics, guided by long-term planning documents which still largely focus on these questions. This report seeks to provide a status update on each question, and to outline what space-based facilities are crucial for future progress, intended to guide NASA's preparatory work for the Astro2030 Decadal.

Ultra-long gamma-ray bursts (ULGRBs) and luminous fast blue optical transients (LFBOTs) are two rare classes of engine-driven transients whose physical connection remains unknown. It has been suggested that both may arise from the mergers of a massive helium core with a compact object. We investigate this common origin by reanalyzing the optical counterpart of the highly unusual GRB 111209A/SN 2011kl associated with an ULGRB in the context of a recently developed, analytical LFBOT model. We find that SN 2011kl is broadly consistent with an LFBOT origin, exhibiting a rapid, luminous and blue early emission. However, compared to the LFBOT population, SN 2011kl features a longer "plateau" of emission 2 weeks post-merger, suggesting an extended pre-merger mass-loss history, as well as stronger UV suppression. We additionally compare the host galaxy environments of five ULGRBs to those of LFBOTs and classical LGRBs. We find that ULGRBs, similar to LFBOTs and long GRBs, tend to occur in lower mass (<10^10 solar masses) galaxies with higher amounts of active star formation than observed for field galaxy populations at similar redshifts. Together, these results support a shared progenitor for at least a subset of ULGRBs and LFBOTs.

We present a comprehensive analysis of the host galaxies of 11 luminous fast blue optical transients (LFBOTs). We model new and archival host photometry and spectroscopy with Prospector. We determine that all LFBOT hosts are actively star-forming with recent bursts of star formation and have a median stellar mass of log(M*/M circle dot)=9.61-1.61+0.74 , present-day star formation rate SFR = 0.99-0.95+14.85 M circle dot yr-1, and gas-phase oxygen abundance metallicity 12+log(O/H) = 8.59-0.22+0.18 . To contextualize these results, we compare them to the host properties of hydrogen-poor superluminous supernovae (SLSNe-I), several core-collapse supernova (CCSN)subtypes (SNe Ibc, II, and Ibn), and long gamma-ray bursts (LGRBs). We find that LFBOT hosts are more star-forming than CCSN hosts, but less star-forming than SLSN-I hosts. We further show that LFBOT hosts are more metal-poor than SN Ibc and II hosts, but more metal-rich than SLSN-I and LGRB hosts. Finally, we find that, similar to SLSNe-I and unlike CCSNe and LGRBs, a large fraction of LFBOTs occur in their hosts' faintest pixel or outside their host galaxy's light. Our results indicate that LFBOTs have a massive stellar origin that does not trace active star-forming regions within their hosts and have a weaker metallicity-dependence than other extreme transients. For these reasons, we favor a compact-object and Wolf-Rayet star merger progenitor scenario over other previously proposed models, such as tidal disruption events and failed or successful CCSN. Future discoveries of LFBOTs with the Rubin Observatory will help to increase their sample size and place firmer constraints on their environments and progenitors.

Two time domain surveys, recently funded as part of the Eric and Wendy Schmidt Observatory System; the Argus Array, in the optical, and the Deep Synoptic Array (DSA), in the radio, will transform gamma-ray burst (GRB) science via the serendipitous discovery of hundreds of GRB afterglows per year. In this work, we simulate DSA and Argus observations of GRB afterglows. We find that, of the long-duration GRBs (LGRBs) detected by the Fermi Gamma-ray Burst Monitor, (26±3)

Cosmic explosions play a critical role in a broad range of astrophysical fields. Although considerable progress has been made to understand the explosive engines and their progenitors, many of the details are not well understood. One of the most powerful electromagnetic probes of the explosive mechanism and the stellar progenitor is the first burst of photons emitted from this blastwave as it exits the stellar photosphere, known as shock breakout (SBO). Our understanding of SBO has evolved considerably in the past decade. Shock heating as the blastwave propagates through the star and circumstellar material can drastically alter this emission producing a much broader range of potential SBO signals than that predicted by standard analytical approaches. Here we present a semi-analytic approach to model this diverse SBO emission, focused on thermal Bremsstrahlung radiation, which more accurately captures the complexities in Nature over previous treatments. We calculate a range of signals for a range of supernova and gamma-ray burst types. Our models demonstrate how we can use these signals to place constraints on the nature of the explosive engines and better understand the role SBO can play in prompt gamma-ray bursts. We study the implications of these results to historic observations, Einstein Probe transients, and in the context of proposed missions. We find that stripped envelope events can be detected serendipitously with survey telescopes, but type Ia and II SBO detections require fast-pointing X-ray observations in response to early warning alerts from gravitational wave or neutrino detectors.

Magnetar giant flares (MGFs) are rare, extremely bright bursts of gamma rays from highly magnetized neutron stars. These events are challenging to identify because, at extragalactic distances, they can appear similar to other astrophysical phenomena. Only a handful have been confidently identified to date, limiting our understanding of their origin and physical properties. This study focuses on expanding the sample of known events and enabling a more detailed characterization of their observational features and intrinsic properties while introducing significant improvements to the methods used to identify and analyze them. When applied to archival data from the Gamma-ray Burst Monitor (GBM) on the Fermi Gamma-ray Space Telescope, our approach added four previously unidentified events to the known sample, expanding the total to 13 MGFs. This demonstrates both the effectiveness of the method and the likelihood that additional MGFs remain hidden in existing gamma-ray burst catalogs. We utilized this expanded sample to gain a deeper understanding of the broader population of MGFs. We developed a statistical modeling framework that combines previously considered data with modern observations from Fermi/GBM. The model accounts for instrumental sensitivity and the expected diversity in event characteristics. We inferred a volumetric rate of events above 1.2 & times; 10(44) erg of R-MGF = 5.5(-2.7)(+4.5) & times; 10(5) Gpc(-3) yr(-1). The results show that individual magnetars must produce multiple flares throughout their lifetimes, reinforcing the idea that these are recurring phenomena rather than singular explosive events. Expanding the sample of known MGFs improves our understanding of magnetars and their role in other astrophysical phenomena, including possible links to fast radio bursts, gravitational waves, and the creation of heavy elements in extreme astrophysical environments.

We present the discovery of EP250827b/SN 2025wkm, an X-ray Flash (XRF) discovered by the Einstein Probe (EP), accompanied by a broad-line Type Ic supernova (SN Ic-BL) at z = 0.1194. EP250827b possesses a prompt X-ray luminosity of ∼ 10^45 erg s^-1, lasts over 1000 seconds, and has a peak energy E_p < 1.5 keV at 90% confidence. SN 2025wkm possesses a double-peaked optical light curve (LC), though its bolometric luminosity plateaus after its initial peak for ∼ 20 days, consistent with a central engine injecting additional energy into the explosion. Its spectrum transitions from a blue to red continuum with clear blueshifted broad absorption features consistent with a SN Ic-BL classification. We do not detect any transient radio emission and rule out the existence of an on-axis, energetic jet ≳ 10^50erg assuming a typical LGRB circumburst constant density (n ≈ 10^-3–10^-1 cm^-3) and microphysical parameters (ε_ e = 0.1 and ε_ B = 0.01). In the model we invoke, the collapse gives rise to a long-lived magnetar, potentially surrounded by an accretion disk. Magnetically–driven winds from the magnetar and the disk mix together and break out with a velocity ∼ 0.35c and interact with an extended circumstellar medium with radius ∼ 10^13 cm, generating X-ray breakout emission through non-thermal free-free processes. The disk outflows and magnetar winds power blackbody photospheric emission as they cool adiabatically and thermalize, producing the first SN peak. The spin-down luminosity of the magnetar and radioactive decay of ^56Ni powers the late-time emission. We end by discussing the landscape of XRF-SNe within the context of EP's recent discoveries.

Magnetar short bursts (SBs) are hard X-ray transients of durations 0.01-1 s peaking at ∼ 10-100 keV, and are prime targets for new high-energy missions and polarimeters. The recent association of SBs with bright radio bursts in SGR 1935+2154 has broadened interest in SB physics. We present new advanced fireball models combining general relativistic light bending, polarized transport in magnetized photospheres, magnetic photon splitting attenuation, and magnetospheric vacuum birefringence. These models also have relevance to trapped fireballs in magnetar giant flare pulsating tails. We adopt confined flux tube geometries consistent with adiabatic fireballs, and anisotropic/polarized emergent intensities to produce spectra and polarizations, and energy-time Stokes impulse responses. We predict that most fireballs are highly linearly polarized, especially when vacuum birefringence is important. There is rich potential for diagnostics: coexisting direct and lensed delayed images, gaps by occultation of the neutron star surface, and Shapiro+Rømer delay with temporal caustics. These effects can imprint spin phase dependence of the spectral and polarization character of bursts. Predicted signatures depend strongly on viewing geometry, fireball configuration, and photon splitting assumptions, yielding large variance in model high-energy spectral shapes and cutoffs, and energy-dependent polarization. The models can reproduce established double-blackbody SB spectral phenomenology, and we find that the unusual April 2020 radio-associated SB from SGR 1935+2154 is broadly consistent with a footpoint close to the magnetic pole, and possibly near pole-on viewing geometry. Our models motivate reverberation-style analyses for SBs and suggest that high-quality data might constrain source geometry, burst crustal footpoints, and, potentially, neutron star masses and radii.

We investigate the nuclear γ-ray line emission from rare isotopes produced in the astrophysical intermediate neutron-capture process (i process) and assess the prospects of observing these emissions with γ-ray telescopes. The astrophysical sites of the i process remain uncertain, but two candidates with predicted rapid mass ejections at metallicities of stars in the solar neighborhood are post-asymptotic giant branch (post-AGB) stars, such as Sakurai's object (V4334 Sagittarii), and rapidly-accreting white dwarfs (RAWDs). Detailed 1D and 3D simulations indicate that the convective-reactive fluid dynamics responsible for i-process nucleosynthesis can lead to violent, non-radial outbursts resulting in mass ejections of i-process products. We calculate ejected yields of rare isotopes whose radioactive decays may produce detectable γ-ray lines, particularly in the 0.5-2 MeV range, focusing on ^22Na, ^89Sr, and ^95Zr. We estimate the formation rates of these sources and the likelihood of detecting their γ-ray emissions within 1000 parsecs of the Sun. The probability of observing i-process emission lines during COSI's operational period is up to ≈ 1%, rising to 11% for ^89Sr if observed within a few days. Due to the long lifetime and large production of ^22Na from proton-capture reactions its detection is more likely, with a probability of ≈ 5%. Future space missions could increase the observation probability to several tens of percent. Detection of long-lived neutron-rich isotopes such as ^137Cs would provide the first direct γ-ray signature of intermediate neutron-density nucleosynthesis, distinguishing the i process from classical s- and r-process pathways. (abridged)