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 multiwavelength analysis of ZTF23abelseb (AT 2023sva), an optically discovered fast-fading (Delta m(r)=2.2 mag in Delta t=0.74 d), luminous (M-r similar to-30.0 mag), and red (g-r=0.50 mag) transient at z=2.28 with accompanying luminous radio emission. AT 2023sva does not possess a gamma-ray burst (GRB) counterpart to an isotropic equivalent energy limit of E-gamma,(iso)<1.6x10(52) erg, determined through searching gamma-ray satellite archives between the last non-detection and first detection, making it the sixth example of an optically discovered afterglow with a redshift measurement and no detected GRB counterpart. We analyse AT 2023sva's optical, radio, and X-ray observations to characterize the source. From radio analyses, we find the clear presence of strong interstellar scintillation (ISS) 72 d after the initial explosion, allowing us to place constraints on the source's angular size and bulk Lorentz factor. When comparing the source sizes derived from ISS of orphan events to those of the classical GRB population, we find orphan events have statistically smaller source sizes. We also utilize Bayesian techniques to model the multiwavelength afterglow. Within this framework, we find evidence that AT 2023sva possesses a shallow power-law structured jet viewed slightly off-axis (theta(v)=0.07 +/- 0.02) just outside of the jet's core opening angle (theta(c)=0.06 +/- 0.02). We determine this is likely the reason for the lack of a detected GRB counterpart, but also investigate other scenarios. AT 2023sva's evidence for possessing a structured jet stresses the importance of broadening orphan afterglow search strategies to a diverse range of GRB jet angular energy profiles, to maximize the return of future optical surveys.

Long gamma-ray bursts (GRBs) are believed to originate from core collapse of massive stars. High-redshift GRBs can probe the star formation and reionization history of the early Universe, but their detection remains rare. Here we report the detection of a GRB triggered in the 0.5–4 keV band by the Wide-field X-ray Telescope (WXT) on board the Einstein Probe (EP) mission, designated as EP240315a, whose bright peak was also detected by the Swift Burst Alert Telescope and Konus-Wind through off-line analyses. At a redshift of z = 4.859, EP240315a showed a much longer and more complicated light curve in the soft-X-ray band than in gamma rays. Benefiting from a large field of view ( 3,600°2) and a high sensitivity, EP-WXT captured the earlier engine activation and extended late engine activity through a continuous detection. With a peak X-ray flux at the faint end of previously known high-z GRBs, the detection of EP240315a demonstrates the great potential for EP to study the early universe via GRBs. The death of massive stars has traditionally been discovered by explosive events in the gamma-ray band. Liu et al. show that the sensitive wide-field monitor on board Einstein Probe can reveal a weak soft-X-ray signal much earlier than gamma rays.

Classical gamma-ray bursts (GRBs) have two distinct emission episodes: prompt emission from ultrarelativistic ejecta and afterglow from shocked circumstellar material. While both components are extremely luminous in known GRBs, a variety of scenarios predict the existence of luminous afterglow emission with little or no associated high-energy prompt emission. We present AT 2019pim, the first spectroscopically confirmed afterglow with no observed high-energy emission to be identified. Serendipitously discovered during follow-up observations of a gravitational-wave trigger and located in a contemporaneous TESS sector, it is hallmarked by a fast-rising (t approximate to 2 h), luminous (M-UV,M-peak approximate to-24.4 mag) optical transient with accompanying luminous X-ray and radio emission. No gamma-ray emission consistent with the time and location of the transient was detected by Fermi-GBM or by Konus, placing constraining limits on an accompanying GRB. We investigate several independent observational aspects of the afterglow in the context of constraints on relativistic motion and find all of them are consistent with an initial Lorentz factor of Gamma(0)approximate to 10-30 for the on-axis material, significantly lower than in any well-observed GRB and consistent with the theoretically predicted 'dirty fireball' scenario in which the high-energy prompt emission is stifled by pair production. However, we cannot rule out a structured jet model in which only the line-of-sight material was ejected at low-Gamma, off-axis from a classical high-Gamma jet core, and an on-axis GRB with below-average gamma-ray efficiency also remains a possibility. This event represents a milestone in orphan afterglow searches, demonstrating that luminous optical afterglows lacking detected GRB counterparts can be identified and spectroscopically confirmed in real time.

The afterglow emission of gamma-ray bursts (GRBs) originates from deceleration of the ultra-relativistic matter in the circumburst medium. Observations of afterglow in the high-energy and very high-energy domains provide essential information about the physics of acceleration in relativistic shocks. The lack of sensitivity in the mega-electronvolt gamma rays in the afterglow phase prevents us from constraining the spectral turnover from the X-ray to tera-electronvolt energies. GRB 221009A offers the unique opportunity to characterize spectral components during the prompt and early afterglow phases and probe their origin, including mega-electronvolt observations. Analyzing the multiwave band afterglow emission, we identified two distinct spectral components during the initial 30 minutes. The second spectral component peaks at similar to 100 GeV, and the bolometric fluence (10 MeV-10 TeV) is greater than 2 x 10(-3) erg/cm(2). Performing broadband spectral modeling, we provide constraints on the magnetic field (similar to 0.1 G) and the energies of the accelerated electrons in the external relativistic shock.

In this catalogue, we present the results of a systematic study of 199 short gamma-ray bursts (GRBs) detected by Konus-Wind between 1 January 2011 and 31 August 2021. The catalogue extends the Second Catalogue of short GRBs covering the period 1994-2010 by ten years of data. The resulting Konus-Wind short GRB sample includes 494 bursts. From temporal and spectral analyses of the sample, we provide the burst durations, spectral lags, estimates of the minimum variability timescales, rise and decay times, the results of spectral fits with three model functions, the total energy fluences, and the peak energy fluxes of the bursts. We present statistical distributions of these parameters for the complete set of 494 short GRBs detected in 1994-2021. We discuss in detail the properties of the bursts with extended emission in the context of the whole short GRB population. Finally, we consider the results in the context of the Type I (merger-origin)/Type II (collapsar-origin) classification and discuss the extragalactic magnetar giant flare subsample.

Magnetar giant flares (MGFs) are the extremely short, energetic transients originating from highly magnetized neutron stars. When observed in nearby galaxies, these rare events are nearly indistinguishable from cosmological short gamma-ray bursts. We present the analysis of GRB 231115A, a candidate extragalactic MGF observed by Fermi/GBM and localized by INTEGRAL to the starburst galaxy M82. This burst exhibits distinctive temporal and spectral characteristics, including a short duration and a high peak energy, consistent with known MGFs. Time-resolved analysis reveals rapid spectral evolution and a clear correlation between luminosity and spectral hardness, providing robust evidence of relativistic outflows. Archival Chandra data identified point sources within the GRB 231115A localization consistent with the theoretical maximum persistent emission luminosity, though no definitive counterpart was found. Simulations indicate that any transient emission associated with GRB 231115A would require energies exceeding those of typical magnetar bursts to be detectable by current instruments. While the tail of a MGF originating from outside of the Milky Way and its satellite galaxies has never been detected, analysis suggests that such emission could be observable at M82's distance with instruments like Swift/XRT or NICER, though no tail was identified for this event. These findings underscore the need for improved follow-up strategies and technological advancements to enhance MGF detection and characterization.

We present results of a comprehensive analysis of the polarization characteristics of GRB 200503A and GRB 201009A observed with the Cadmium Zinc Telluride Imager (CZTI) on board AstroSat. Despite these GRBs being reasonably bright, they were missed by several spacecraft and had thus far not been localized well, hindering polarization analysis. We present positions of these bursts obtained from the Inter-Planetary Network (IPN) and the newly developed CZTI localization pipeline. We then undertook polarization analyses using the standard CZTI pipeline. We cannot constrain the polarization properties for GRB 200503A, but find that GRB 201009A has a high degree of polarization.

Observing and understanding the origin of the very-high-energy (VHE) spectral component in gamma-ray bursts (GRBs) has been challenging because of the lack of sensitivity in MeV-GeV observations, so far. The majestic GRB 221009A, known as the brightest of all times (BOAT), offers a unique opportunity to identify spectral components during the prompt and early afterglow phases and probe their origin. Analyzing simultaneous observations spanning from keV to TeV energies, we identified two distinct spectral components during the initial 20 minutes of the burst. The second spectral component peaks between 10-300 GeV, and the bolometric fluence (10 MeV-10 TeV) is estimated to be greater than 2×10^-3 erg/ cm^2. Performing broad-band spectral modeling, we provide constraints on the magnetic field and the energies of electrons accelerated in the external relativistic shock. We interpret the VHE component as an afterglow emission that is affected by luminous prompt MeV radiation at early times.

Magnetars are slowly rotating neutron stars that possess the strongest magnetic fields ($10^{14}-10^{15} \mathrm{G}$) known in the cosmos. They display a range of transient high-energy electromagnetic activity. The brightest and most energetic of these events are the gamma-ray bursts (GRBs) known as magnetar giant flares (MGFs), with isotropic energy $E\approx10^{44}-10^{46} \mathrm{erg}$. There are only seven detections identified as MGFs to date: three unambiguous events occurred in our Galaxy and the Magellanic Clouds, and the other four MGF candidates are associated with nearby star-forming galaxies. As all seven identified MGFs are bright at Earth, additional weaker events remain unidentified in archival data. We conducted a search of the Fermi Gamma-ray Burst Monitor (GBM) database for candidate extragalactic MGFs and, when possible, collected localization data from the Interplanetary Network (IPN) satellites. Our search yielded one convincing event, GRB 180128A. IPN localizes this burst with NGC 253, commonly known as the Sculptor Galaxy. This event is the second MGF in modern astronomy to be associated with this galaxy and the first time two bursts are associated with a single galaxy outside our own. Here, we detail the archival search criteria that uncovered this event and its spectral and temporal properties, which are consistent with expectations for a MGF. We also discuss the theoretical implications and finer burst structures resolved from various binning methods. Our analysis provides observational evidence for an eighth identified MGF.

GRB 221009A has been referred to as the brightest of all time (BOAT). We investigate the veracity of this statement by comparing it with a half century of prompt gamma-ray burst observations. This burst is the brightest ever detected by the measures of peak flux and fluence. Unexpectedly, GRB 221009A has the highest isotropic-equivalent total energy ever identified, while the peak luminosity is at the ∼99th percentile of the known distribution. We explore how such a burst can be powered and discuss potential implications for ultralong and high-redshift gamma-ray bursts. By geometric extrapolation of the total fluence and peak flux distributions, GRB 221009A appears to be a once-in-10,000-year event. Thus, it is almost certainly not the BOAT over all of cosmic history; it may be the brightest gamma-ray burst since human civilization began.

We report preliminary results of the search in the Konus-Wind experiment data for hard X-ray/soft & gamma;-ray emission in coincidence with publicly reported fast radio bursts (FRBs). We find no significant associations for any of the 581 FRBs in our sample and report upper limits to the high-energy fluence/peak flux for three spectral shapes, which generally describe short GRB, long GRB and magnetar giant flare spectra. In addition to study each individual FRB, we perform a stacking analysis of the bursts from each repeating source in our sample and a separate stacking analysis of the bursts from the non-repeating FRBs. We find no statistically significant excess of the cumulative emission over background level for either case.

&lt;p&gt;The Atmosphere-Space Interactions Monitor (ASIM) is a mission of the European Space Agency launched in April 2018 and hosted onboard the International Space Station (ISS). ASIM is dedicated to study the physics of Transient Luminous Events (TLEs) and Terrestrial Gamma-ray Flashes (TGFs) and their relation to lightning. TGFs are X- and Gamma-ray flashes associated to lightning discharges, with average duration of few tens of microseconds and energies up to 40 MeV. ASIM detects TGFs by means of the Modular X- and Gamma-ray Sensor (MXGS). So far, the MXGS performance (efficiency, effective area) have been evaluated by Monte Carlo simulations only, while energy calibration is monitored using built-in radioactive sources and background lines. TGFs are local events, very rarely observed by more then one spacecraft simultaneously, therefore it is difficult to use them to validate the MXGS performance. Goal of this study is to use cosmic Gamma-ray Bursts (GRBs) simultaneously detected by ASIM and other spacecraft as calibration sources to validate the spectral performance of MXGS. GRBs are the brightest explosions in the universe, associated to the collapse of massive stars or the merger of compact objects, involving at least one neutron star, at cosmological distances. During the period from June 2018 to December 2021, 12 GRBs were detected by ASIM and by one or more other spacecraft. Here we use data from the Konus-WIND mission and from the Fermi Gamma Burst Monitor (GBM), both considered as benchmarks in the field of GRB analysis. We cross-correlate the light curves of the three instruments, and we perform simultaneous spectral analysis using the forward-folding approach. In some cases, we find good consistency between the detectors, indicating an overall validation of the MXGS performance. In other cases, we identified discrepancies, possibly due to absorption from structures of the ISS, currently under investigation. In this presentation, we show our data sample, the methodology used and the preliminary joint spectral analysis results. This work is relevant because it will provide an independent assessment of the MXGS performance, with clear implications for ASIM TGF results.&lt;/p&gt;

Cadmium Zinc Telluride Imager (CZTI) aboard AstroSat has been regularly detecting Gamma-Ray Bursts (GRBs) since its launch in 2015. Its sensitivity to polarization measurements at energies above 100 keV allows CZTI to attempt spectro-polarimetric studies of GRBs. Here, we present the first catalog of GRB polarization measurements made by CZTI during its first five years of operation. This presents the time integrated polarization measurements of the prompt emission of 20 GRBs in the energy range 100-600 keV. The sample includes the bright GRBs which were detected within an angle range of 0-60 degree and 120-180 degree where the instrument has useful polarization sensitivity and is less prone to systematics. We implement a few new modifications in the analysis to enhance polarimetric sensitivity of the instrument. Majority of the GRBs in the sample are found to possess less / null polarization across the total bursts' duration in contrast to a small fraction of five GRBs exhibiting high polarization. The low polarization across the bursts can be speculated to be either due to the burst being intrinsically weakly polarized or due to varying polarization angle within the burst even when it is highly polarized. In comparison to POLAR measurements, CZTI has detected a larger number of cases with high polarization. This may be a consequence of the higher energy window of CZTI observations which results in the sampling of smaller duration of burst emissions in contrast to POLAR, thereby, probing emissions of less temporal variations of polarization properties.

We present a detailed follow-up of the very energetic GRB 210905A at a high redshift of z = 6.312 and its luminous X-ray and optical afterglow. We obtained a photometric and spectroscopic follow-up in the optical and near-infrared (NIR), covering both the prompt and afterglow emission from a few minutes up to 20 Ms after burst. With an isotropic gamma-ray energy release of Eiso = 1.27E54 erg, GRB 210905A lies in the top ~7% of gamma-ray bursts (GRBs) in terms of energy released. Its afterglow is among the most luminous ever observed. It starts with a shallow evolution that can be explained by energy injection, and it is followed by a steeper decay, while the spectral energy distribution is in agreement with slow cooling in a constant-density environment within the standard fireball theory. A jet break at ~ 46.2+-16.3 d (~6.3 d rest-frame) has been observed in the X-ray light curve; however, it is hidden in the H band due to the contribution from the likely host galaxy, the fourth GRB host at z > 6 known to date. We derived a half-opening angle of 8.4+-1.0 degrees, which is the highest ever measured for a z>6 burst, but within the range covered by closer events. The resulting collimation-corrected gamma-ray energy release of 1E52 erg is also among the highest ever measured. The moderately large half-opening angle argues against recent claims of an inverse dependence of the half-opening angle on the redshift. The total jet energy is likely too large to be sustained by a standard magnetar, and it suggests that the central engine of this burst was a newly formed black hole. Despite the outstanding energetics and luminosity of both GRB 210905A and its afterglow, we demonstrate that they are consistent with those of less distant bursts, indicating that the powering mechanisms and progenitors do not evolve significantly with redshift.

Dirty fireballs are a hypothesized class of relativistic massive-star explosions with an initial Lorentz factor Gamma(init) below the Gamma(init) similar to 100 required to produce a long-duration gamma-ray burst (LGRB), but which could still produce optical emission resembling LGRB afterglows. Here we present the results of a search for on-axis optical afterglows using the Zwicky Transient Facility (ZTF). Our search yielded seven optical transients that resemble on-axis LGRB afterglows in terms of their red colors (g - r > 0 mag), faint host galaxies (r > 23 mag), rapid fading (dr/dt > 1 mag day(-1)), and in some cases X-ray and radio emission. Spectroscopy of the transient emission within a few days of discovery established cosmological distances (redshift z = 0.876 to 2.9) for six of the seven events, tripling the number of afterglows with redshift measurements discovered by optical surveys without a gamma-ray trigger. A likely associated LGRB (GRB 200524A, GRB 210204A, GRB 210212B, and GRB 210610B) was identified for four events (ZTF 20abbiixp/AT 2020kym, ZTF 21aagwbjr/AT 2021buv, ZTF 21aakruew/AT 2021cwd, and ZTF 21abfmpwn/AT 2021qbd) post facto, while three (ZTF 20aajnksq/AT 2020blt, ZTF 21aaeyldq/AT 2021any, and ZTF 21aayokph/AT 2021lfa) had no detected LGRB counterpart. The simplest explanation for the three "orphan" events is that they were regular LGRBs missed by high-energy satellites owing to detector sensitivity and duty cycle, although it is possible that they were intrinsically subluminous in gamma-rays or viewed slightly off-axis. We rule out a scenario in which dirty fireballs have a similar energy per solid angle to LGRBs and are an order of magnitude more common. In addition, we set the first direct constraint on the ratio of the opening angles of the material producing gamma-rays and the material producing early optical afterglow emission, finding that they must be comparable.

We present a database of solar flares registered by the Konus-Wind instrument during more than 27 yr of operation, from 1994 November to now (2022 June). The constantly updated database (hereafter KW-Sun) contains over 1000 events detected in the instrument’s triggered mode and is accessible online at http://www.ioffe.ru/LEA/kwsun/. For each flare, the database provides time-resolved energy spectra in energy range from ∼20 keV to ∼15 MeV in FITS format along with count-rate light curves in three wide-energy bands, G1 (∼20–80 keV), G2 (∼80–300 keV), and G3 (∼300–1200 keV), with high time resolution (down to 16 ms) in ASCII and IDL SAV formats. This article focuses on the instrument capabilities in the context of solar observations, the structure of the KW-Sun data, and their intended usage. The presented homogeneous data set obtained in the broad energy range with high temporal resolution during more than two full solar cycles is beneficial for both statistical and case studies as well as a source of context data for solar flare research.

Gamma-ray bursts (GRBs) are short and intense flashes of γ-rays coming from deep space. GRBs were discovered more than a half century ago and now are observed across the whole electromagnetic spectrum from radio to very-high-energy gamma rays. They carry information about the powerful energy release during the final stage of stellar evolution, as well as properties of matter on the way to the observer. At present, space-based observatories detect on average approximately one GRB per day. In this review, we summarize key space and ground facilities that contribute to the GRB studies.

We present the catalog of InterPlanetary Network (IPN) localizations for 199 short-duration gamma-ray bursts (sGRBs) detected by the Konus-Wind (KW) experiment between 2011 January 1 and 2021 August 31, which extends the initial sample of IPN-localized KW sGRBs to 495 events. We present the most comprehensive IPN localization data on these events, including probability sky maps in Hierarchical Equal Area isoLatitude Pixelization format.

The emission region of γ -ray bursts (GRBs) is poorly constrained. The uncertainty on the size of the dissipation site spans over 4 orders of magnitude (10 12 –10 17 cm) depending on the unknown energy composition of the GRB jets. The joint multiband analysis from soft X-rays to high energies (up to ∼1 GeV) of one of the most energetic and distant GRBs, GRB 220101A ( z = 4.618), allows us to make an accurate distinction between prompt and early afterglow emissions. The enormous amount of energy released by GRB 220101A ( E iso ≈ 3 × 10 54 erg) and the spectral cutoff at E cutoff = 85 − 26 + 16 MeV observed in the prompt emission spectrum constrain the parameter space of the GRB dissipation site. We put stringent constraints on the prompt emission site, requiring 700 < Γ 0 < 1160 and R γ ∼ 4.5 × 10 13 cm. Our findings further highlight the difficulty of finding a simple self-consistent picture in the electron–synchrotron scenario, favoring instead a proton–synchrotron model, which is also consistent with the observed spectral shape. Deeper measurements of the time variability of GRBs, together with accurate high-energy observations (MeV–GeV), would unveil the nature of the prompt emission.