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Gamma-ray bursts (GRBs) can be studied with their linearly dependent parameters alongside the standard |$T_{90}$| distribution. The generalized linear model (GLM) identifies the number of linear dependences in a two-parameter space. Classically, GRBs are classified into two classes by the presence of bimodality in the histogram of |$T_{90}$|⁠. However, additional classes and different features of GRBs are fascinating topics to explore. In this work, we investigate GRB features in the |$T_{90} {-}T_{50}$| plane using the GLM for three major catalogues: Swift , the Fermi Gamma-ray Burst Monitor (GBM), and the Burst And Transient Source Experiment (BATSE). This study shows five linear features for the Fermi GBM catalogue and four linear features for the BATSE catalogue, directing us towards the possibility of non-Gaussianity in the light curves of GRBs. [ABSTRACT FROM AUTHOR]

We study the properties of long gamma-ray burst (GRB) host galaxies using a statistical modelling framework derived to model damped Lyman- |$\alpha$| absorbers (DLAs) in quasar spectra at high redshift. The distribution of |$N_{\rm H\, {\small I}}$| for GRB-DLAs is |$\sim$| 10 times higher than what is found for quasar-DLAs at similar impact parameters. We interpret this as a temporal selection effect due to the short-lived GRB progenitor probing its host at the onset of a starburst where the interstellar medium may exhibit multiple overdense regions. Owing to the larger |$N_{\rm H\, {\small I}}$|⁠ , the dust extinction is larger with 29 per cent of GRB-DLAs exhibiting |$A(V)\gt 1$|  mag in agreement with the fraction of 'dark bursts'. Despite the differences in |$N_{\rm H\, {\small I}}$| distributions, we find that high-redshift |$2 \lt z \lt 3$| quasar- and GRB-DLAs trace the luminosity function of star-forming host galaxies in the same way. We propose that their differences may arise from the fact that the galaxies are sampled at different times in their star formation histories, and that the absorption sightlines probe the galaxy haloes differently. Quasar-DLAs sample the full H  i cross-section, whereas GRB-DLAs sample only regions hosting cold neutral medium. Previous studies have found that GRBs avoid high-metallicity galaxies (⁠|$\sim$| 0.5  |$Z_{\odot }$|⁠). Since at these redshifts galaxies on average have lower metallicities, our sample is only weakly sensitive to such a threshold. Lastly, we find that the modest detection rate of cold gas (H |$_2$| or C  i) in GRB spectra can be explained mainly by a low volume filling factor of cold gas clouds and to a lesser degree by destruction from the GRB explosion itself. [ABSTRACT FROM AUTHOR]

The coalescence of binary neutron stars (BNS) is a prolific source of gravitational waves (GWs) and electromagnetic (EM) radiation, offering a dual observational window into the Universe. Lowering the signal-to-noise ratio (S/N) threshold is a simple and cost-effective way to enhance the detection probability of GWs from BNS mergers. In this study, we introduce a metric of the purity of joint GW and EM detections |$P_{\rm joint}$|⁠ , which is in analogue to |$P_{\rm astro}$| in GW-only observations. By simulating BNS merger GWs jointly detected by the Handford, LIGO Livingston, and Virgo network and EM counterparts (kilonovae and short gamma-ray bursts, sGRBs) with an assumed merger rate density of BNS, we generate catalogues of GW events and EM counterparts. Through this simulation, we analyse joint detection pairs, both correct and misidentified. We find the following: (1) For kilonovae, requiring |$P_{\rm joint}\gt $| 95 per cent instead of |$P_{\rm astro}\gt 95~{{\ \rm per\ cent}}$| reduces the S/N from 9.2 to 8.5–8.8, allowing 5–13 additional joint detections per year and increasing the GW detection volume by 9–17 per cent. (2) For sGRBs, requiring |$P_{\rm joint}\gt $| 95 per cent instead of |$P_{\rm astro}$| reduces the S/N from 9.2 to 8.1–8.5. (3) Increasing kilonova or sGRB detection capability does not improve |$P_{\rm joint}$| due to a higher rate of misidentifications. We also show that sub-threshold GW and kilonova detections can reduce the uncertainty in measuring the Hubble constant to 89–92 per cent of its original value, and sub-threshold GW and sGRB observations can enhance the precision of constraining the speed of GWs to 88 per cent of previously established values. [ABSTRACT FROM AUTHOR]

The stellar initial mass function (IMF) represents a fundamental quantity in astrophysics and cosmology describing the mass distribution of stars from low mass all the way up to massive and very massive stars. It is intimately linked to a wide variety of topics, including stellar and binary evolution, galaxy evolution, chemical enrichment, and cosmological reionization. Nonetheless, the IMF still remains highly uncertain. In this work, we aim to determine the IMF with a novel approach based on the observed rates of transients of stellar origin. We parametrize the IMF with a simple but flexible Larson shape, and insert it into a parametric model for the cosmic UV luminosity density, local stellar mass density, type Ia supernova (SN Ia), core-collapse supernova (CCSN), and long gamma-ray burst (LGRB) rates as a function of redshift. We constrain our free parameters by matching the model predictions to a set of empirical determinations for the corresponding quantities via a Bayesian Markov Chain Monte Carlo method. Remarkably, we are able to provide an independent IMF determination with a characteristic mass m c = 0. 10 − 0.08 + 0.24 M ⊙ and high-mass slope ξ = − 2. 53 − 0.27 + 0.24 that are in accordance with the widely used IMF parameterizations (e.g., Salpeter, Kroupa, Chabrier). Moreover, the adoption of an up-to-date recipe for the cosmic metallicity evolution allows us to constrain the maximum metallicity of LGRB progenitors to Z m a x = 0. 12 − 0.05 + 0.29 Z ⊙ . We also find which progenitor fraction actually leads to SN Ia or LGRB emission (e.g., due to binary interaction or jet-launching conditions), put constraints on the CCSN and LGRB progenitor mass ranges, and test the IMF universality. These results show the potential of this kind of approach for studying the IMF, its putative evolution with the galactic environment and cosmic history, and the properties of SN Ia, CCSN, and LGRB progenitors, especially considering the wealth of data incoming in the future. [ABSTRACT FROM AUTHOR]

Based on the results of several articles devoted to the study of the average power spectra () of γ-ray bursts (GRBs), a list of features has been compiled that need to be explained. Using the possibility, proven in a number of publications, of decomposing the time profile of each γ-ray burst into the sum of several two-sided pulses, GRB modeling is performed in the time domain and the study of the average power spectra of models is carried out in the frequency domain. Brief reviews of the results of a number of theoretical works are made. A Monte Carlo simulation of time series consisting of a set of two-sided pulses with a Poisson distribution of the position of the pulses on the time scale, with different pulse shapes and distributions of amplitude and pulse duration, was carried out. All the basic properties of the average power spectrum in the form of a quasi-Lorentzian theoretically derived in various published studies have been confirmed. of superposition of two-sided pulses randomly distributed over time are not described by a single power law. In general, the shape consists of three quasi-power sections separated by two breaks. The position of the two breaks in the is determined by the parameters of asymmetry and the effective pulse duration. The pulse-duration distribution and their shape affect the shape of the , and the pulse amplitude distribution has practically no such effect. The amount of intermittency (at large values of γ ≥ 1) affects the shape of the . Based on previous theoretical work and the Monte Carlo simulations carried out in this study, it can be argued that all the features of the average power spectra of GRBs are explained using a simple light curve model in the form of a superposition of uncorrelated random two-sided pulses. The main features of the of GRBs are determined only by such pulse characteristics as the asymmetry parameter, the duration distribution, and the shape of the pulses. [ABSTRACT FROM AUTHOR]

The behaviour of a short gamma-ray burst (sGRB) afterglow light curve can reveal the angular structure of the relativistic jet and constrain the observer's viewing angle |$\theta _\textrm {obs}$|⁠. The observed deceleration time of the jet, and, therefore, the time of the afterglow peak, depends on the observer's viewing angle. A larger viewing angle leads to a later peak of the afterglow and a lower flux at peak. We utilize the earliest afterglow detections of 58 sGRBs detected with the Neil Gehrels Swift Observatory X-ray Telescope to constrain the ratio of the viewing angle |$\theta _\textrm {obs}$| to the jet's core |$\theta _\textrm {c}$|⁠. We adopt a power-law angular jet structure in both energy |$E(\theta)\propto \theta ^{-a}$| and Lorentz factor |$\Gamma (\theta)\propto \theta ^{-b}$| beyond the core. We find that either sGRBs are viewed within |$\theta _\textrm {obs}/\theta _\textrm {c}\lt 1$| or the initial Lorentz factor of material in their jet's core is extremely high (⁠|$\Gamma _0\gt 500$|⁠). If we consider tophat jets, we constrain 90 per cent of our sample to be viewed within |$\theta _\textrm {obs}/\theta _\textrm {c}\lt 1.06$| and 1.15 for our canonical and conservative afterglow scenarios. For a subset of events with measurements of the jet break, we can constrain |$\Gamma _0\theta _\textrm {c}\gtrsim 30$|⁠. This confirmation that cosmological sGRBs are viewed either on-axis or very close to their jet's core has significant implications for the nature of the prompt gamma-ray production mechanism and for the rate of future sGRB detections coincident with gravitational waves, implying that they are extremely rare. [ABSTRACT FROM AUTHOR]

According to the hypothesis that strange quark matter may be the true ground state of matter at extremely high densities, strange quark stars should be stable and could exist in the Universe. It is possible that pulsars may actually be strange stars, but not neutron stars. Here we present a short review on recent progresses in the field of strange quark stars. First, three popular phenomenological models widely used to describe strange quark matter are introduced, with special attention being paid on the corresponding equation of state in each model. Combining the equation of state with the Tolman-Oppenheimer-Volkov equations, the inner structure and mass-radius relation can be obtained for the whole sequence of strange stars. Tidal deformability and oscillations (both radial and non-radial oscillations), which are sensitive to the composition and the equations of state, are then described. Hybrid stars as a special kind of quark stars are discussed. Several other interesting aspects of strange stars are also included. For example, strong gravitational wave emissions may be generated by strange stars through various mechanisms, which may help identify strange stars via observations. Especially, close-in strange quark planets with respect to their hosts may provide a unique test for the existence of strange quark objects. Fierce electromagnetic bursts could also be generated by strange stars. The energy may come from the phase transition of neutron stars to strange stars, or from the merger of binary strange stars. The collapse of the strange star crust can also release a huge amount of energy. It is shown that strange quark stars may be involved in short gamma-ray bursts and fast radio bursts. [ABSTRACT FROM AUTHOR]

Gamma-ray burst (GRB), GRB 221009A, a long-duration GRB, was observed simultaneously by the Water Cherenkov Detector Array (WCDA) and the Kilometer Squared Array (KM2A) of the Large High Altitude Air Shower Observatory (LHAASO) during the prompt emission and the afterglow periods. Characteristic multi-TeV photons up to 13 TeV were observed in the afterglow phase. The observed very high-energy (VHE) gamma-ray spectra by WCDA and KM2A during different time intervals and in different energy ranges can be explained very well in the context of the photohadronic model with the inclusion of extragalactic background light models. In the photohadronic scenario, interaction of high-energy protons with the synchrotron self-Compton (SSC) photons in the forward shock region of the jet is assumed to be the source of these VHE photons. The observed VHE spectra from the afterglow of GRB 221009A are similar to the VHE gamma-ray spectra observed from the temporary extreme high-energy peaked BL Lac (EHBL), 1ES 2344+514 only during the 11th and the 12th of August, 2016. Such spectra are new and have been observed for the first time in a GRB. [ABSTRACT FROM AUTHOR]

Short gamma-ray bursts (GRBs) are explosive transients caused by binary mergers of compact objects containing at least one neutron star. Multiwavelength afterglow observations provide constraints on the physical parameters of the jet, its surrounding medium, and the microphysics of the enhanced magnetic fields and accelerated electrons in the blast wave at the front of the jet. The synchrotron radio emission can be tracked for much longer than in other spectral regimes, and it can pin down the evolution of the spectral peak. We present the results of a systematic observing campaign of eight short GRBs with the MeerKAT radio telescope. Additionally, we present observations of four of these short GRBs using the ATCA radio telescope and two of these short GRBs with the e -MERLIN radio telescope. Using these results we report one possible detection of a short GRB afterglow from GRB 230217A and deep upper limits for the rest of our short GRB observations. We use these observations to place constraints on some of the physical parameters, in particular those related to electron acceleration, the circumburst density, and gamma-ray energy efficiency. We discuss how deeper observations with new and upgraded telescopes should be able to determine if the gamma-ray efficiency differs between long and short GRBs. We also report detections of the likely host galaxies for four of the eight GRBs and upper limits for another GRB, increasing the number of detected host galaxies in the radio with implications for the star formation rate in these galaxies. [ABSTRACT FROM AUTHOR]

In this review, we present a self-contained introduction to axion-like particles (ALPs) with a particular focus on their effects on photon polarization: both theoretical and phenomenological aspects are discussed. We derive the photon survival probability in the presence of photon–ALP interaction, the corresponding final photon degree of linear polarization, and the polarization angle in a wide energy interval. The presented results can be tested by current and planned missions such as IXPE (already operative), eXTP, XL-Calibur, NGXP, XPP in the X-ray band and like COSI (approved to launch), e-ASTROGAM, and AMEGO in the high-energy range. Specifically, we describe ALP-induced polarization effects on several astrophysical sources, such as galaxy clusters, blazars, and gamma-ray bursts, and we discuss their real detectability. In particular, galaxy clusters appear as very good observational targets in this respect. Moreover, in the very-high-energy (VHE) band, we discuss a peculiar ALP signature in photon polarization, in principle capable of proving the ALP existence. Unfortunately, present technologies cannot detect photon polarization up to such high energies, but the observational capability of the latter ALP signature in the VHE band could represent an interesting challenge for the future. As a matter of fact, the aim of this review is to show new ways to make progress in the physics of ALPs, thanks to their effects on photon polarization, a topic that has aroused less interest in the past, but which is now timely with the advent of many new polarimetric missions. [ABSTRACT FROM AUTHOR]

The relativistic outflows that produce long gamma-ray bursts (LGRBs) can be described by a structured jet model where prompt |$\gamma$| -ray emission is restricted to a narrow region in the jet's core. Viewing the jet off-axis from the core, a population of afterglows without an associated GRB detection can be predicted. In this work, we conduct an archival search for these 'orphan' afterglows (OAs) with minute-cadence, deep (⁠|$g\sim 23$|⁠) data from the Dark Energy Camera (DECam) taken as part of the Deeper, Wider, Faster programme (DWF). We introduce a method to select fast-evolving OA candidates within DWF data that comprises a machine learning model, based on a realistic synthetic population of OAs. Using this classifier, we recover 51 OA candidates. Of these candidates, 42 are likely flare events from M-class stars. The remaining nine possess quiescent, coincident sources in archival data with angular profiles consistent with a star and are inconsistent with the expected population of LGRB host galaxies. We therefore conclude that these are likely Galactic events. We calculate an upper limit on the rate of OAs down to |$g\lt 22$| AB mag of 7.46 deg |$^{-2}$| yr |$^{-1}$| using our criteria and constrain possible jet structures. We also place an upper limit of the characteristic angle between the |$\gamma$| -ray-emitting region and the jet's half-opening angle. For a smooth power law and a power law with core jet model, respectively, these values are |$58.3^{\circ }$| and |$56.6^{\circ }$|⁠ , for a power-law index of 0.8 and |$75.3^{\circ }$| and |$76.8^{\circ }$| for a power-law index of 1.2. [ABSTRACT FROM AUTHOR]

We present the semi-analytical light curve modelling of 13 supernovae associated with gamma-ray bursts (GRB-SNe) along with two relativistic broad-lined (Ic-BL) SNe without GRB association (SNe 2009bb and 2012ap), considering millisecond magnetars as central-engine-based power sources for these events. The bolometric light curves of all 15 SNe in our sample are well-regenerated utilizing a χ2-minimization code, MINIM , and numerous parameters are constrained. The median values of ejecta mass (M ej), magnetar's initial spin period (P i), and magnetic field (B) for GRB-SNe are determined to be ≈5.2 M⊙, 20.5 ms, and 20.1 × 1014 G, respectively. We leverage machine learning (ML) algorithms to comprehensively compare the three-dimensional parameter space encompassing M ej, P i, and B for GRB-SNe determined herein to those of H-deficient superluminous SNe (SLSNe-I), fast blue optical transients (FBOTs), long GRBs (LGRBs), and short GRBs (SGRBs) obtained from the literature. The application of unsupervized ML clustering algorithms on the parameters M ej, P i, and B for GRB-SNe, SLSNe-I, and FBOTs yields a classification accuracy of ∼95 per cent. Extending these methods to classify GRB-SNe, SLSNe-I, LGRBs, and SGRBs based on P i and B values results in an accuracy of ∼84 per cent. Our investigations show that GRB-SNe and relativistic Ic-BL SNe presented in this study occupy different parameter spaces for M ej, P i, and B than those of SLSNe-I, FBOTs, LGRBs, and SGRBs. This indicates that magnetars with different P i and B can give birth to distinct types of transients. [ABSTRACT FROM AUTHOR]

Gamma-ray bursts (GRBs) are intense and short-lived cosmic explosions. Miniaturised CubeSat-compatible instruments for the study of GRBs are being developed to help bridge the gap in large missions and assist in achieving full sky coverage. CubeSats are small, compact satellites conforming to a design standard and have transformed the space industry. They are relatively low-cost and are developed on fast timescales, which has provided unparalleled access to space. This paper focuses on GMOD, the gamma-ray module, onboard the 2U CubeSat EIRSAT-1, launched on December 1st 2023. GMOD is a scintillation-based instrument with a cerium bromide crystal coupled to an array of sixteen silicon photomultipliers, designed for the detection of GRBs. The characterisation of GMOD in the spacecraft, along with the validation of an updated spacecraft MEGAlib model is presented and this approach can be followed by other CubeSats with similar science goals. The energy resolution of the flight model is 7.07% at 662 keV and the effective area peaks in the tens to hundreds of keV, making it a suitable instrument for the detection of GRBs. An investigation into the instrument's angular response is also detailed. The results from this characterisation campaign are a benchmark for the instrument's performance pre-launch and will be used to compare with the detector's performance in orbit. [ABSTRACT FROM AUTHOR]

Fulfilling the rich promise of rapid advances in time-domain astronomy is only possible through confronting our observations with physical models and extracting the parameters that best describe what we see. Here, we introduce redback ; a Bayesian inference software package for electromagnetic transients. redback provides an object-orientated python interface to over 12 different samplers and over 100 different models for kilonovae, supernovae, gamma-ray burst afterglows, tidal disruption events, engine-driven transients among other explosive transients. The models range in complexity from simple analytical and semi-analytical models to surrogates built upon numerical simulations accelerated via machine learning. redback also provides a simple interface for downloading and processing data from various catalogues such as Swift and FINK. The software can also serve as an engine to simulate transients for telescopes such as the Zwicky Transient Facility and Vera Rubin with realistic cadences, limiting magnitudes, and sky coverage or a hypothetical user-constructed survey or a generic transient for target-of-opportunity observations with different telescopes. As a demonstration of its capabilities, we show how redback can be used to jointly fit the spectrum and photometry of a kilonova, enabling a more powerful, holistic probe into the properties of a transient. We also showcase general examples of how redback can be used as a tool to simulate transients for realistic surveys, fit models to real, simulated, or private data, multimessenger inference with gravitational waves, and serve as an end-to-end software toolkit for parameter estimation and interpreting the nature of electromagnetic transients. [ABSTRACT FROM AUTHOR]

Ion Weibel instability is considered to be the dominant physics for the dissipation in high-Mach number astrophysical shocks such as supernova remnant shocks and gamma-ray burst shocks. We study the instability dependence on various parameters using theory and particle-in-cell simulations. We demonstrate that electron physics determines the saturation level of the Weibel-generated magnetic field, even though the instability is driven by the ions. We discuss the application to astrophysical and laboratory laser experiment environments to clarify the roles of the ion Weibel instability. We develop a model for the isotropization length-scale in Weibel-mediated shocks and compare its value to other characteristic length-scales of each system. We find that electron heating to near equipartition is crucial for the formation of ultrarelativistic Weibel-mediated shocks. On the other hand, our results imply that non-relativistic shocks in the typical interstellar medium are not purely mediated by the Weibel instability. [ABSTRACT FROM AUTHOR]

Neutron star mergers are astrophysical "gold mines," synthesizing over half of the elements heavier than iron through rapid neutron capture nucleosynthesis. The observation of the binary neutron star merger GW170817, detected both in gravitational waves and electromagnetic radiation, marked a breakthrough. One electromagnetic component of this event, the gamma ray burst GRB 170817A, has an unresolved aspect: the characteristics of its prompt gamma-ray emission spectrum. In this work, we investigate that gamma-ray spectra in such GRBs may be influenced by de-excitations from isomeric transitions. Our study begins with a review of current knowledge on GRB structure and of r-process nucleosynthesis in neutron star collisions, focusing on the role of nuclear isomers in these settings. We then test our hypothesis by developing criteria to select representative isomers, based on known solar element abundances, for modeling GRB spectral characteristics. We integrate these criteria into an interactive web page, facilitating the construction and analysis of relevant gamma-ray spectra from isomeric transitions. Our analysis reveals that three isomers -- 90Zr, 207Pb, and 89Y -- stand out for their potential to impact the prompt GRB spectrum due to their specific properties. This information allows us to incorporate nuclear isomer data into astrophysical simulations and calculate isomeric abundances generated by astrophysical r-processes in neutron star mergers and their imprint on the detected signal. [ABSTRACT FROM AUTHOR]

More than fifty years have elapsed from the first discovery of gamma-ray bursts (GRBs) with American Vela satellites, and more than twenty-five years from the discovery with the BeppoSAX satellite of the first X-ray afterglow of a GRB. Thanks to the afterglow discovery and to the possibility given to the optical and radio astronomers to discover the GRB optical counterparts, the long-time mystery about the origin of these events has been solved. Now we know that GRBs are huge explosions, mainly ultra relativistic jets, in galaxies at cosmological distances. Starting from the first GRB detection with the Vela satellites, I will review the story of these discoveries, those obtained with BeppoSAX, the contribution to GRBs by other satellites and ground experiments, among them being Venera, Compton Gamma Ray Observatory, HETE-2, Swift, Fermi, AGILE, MAGIC, H.E.S.S., which were, and some of them are still, very important for the study of GRB properties. Then, I will review the main results obtained thus far and the still open problems and prospects of GRB astronomy. [ABSTRACT FROM AUTHOR]

We consider the final evolutionary stages of a neutron star–black hole pair. According to the current paradigm, such systems eventually coalesce, which in some cases is accompanied by neutron-star tidal disruption. Using analytical methods, we show that the scenario of slow (of the order of several seconds) neutron-star stripping by the black hole is also possible, depending on the system parameters (the initial masses and intrinsic angular momenta of the components, the equation of state for the neutron star). Reaching the lower mass limit (about one tenth of the solar mass), the neutron star explodes to produce a comparatively powerful electromagnetic transient. Our population calculations show that the stripping mechanism is possible in 50–90 of the cases among all coalescing neutron star–black hole pairs, depending on the model assumptions about the evolution of close binary systems (the common-envelope efficiency parameter, the supernova explosion mechanism) and the initial metallicity of the stellar population. Because of the large mass of the ejected material, the kilonova emission in this scenario has good prospects of detection. [ABSTRACT FROM AUTHOR]

The TeV observations of GRB 221009A provided us with a unique opportunity to analyse the contemporaneous phase in which both prompt and afterglow emissions are seen simultaneously. To describe this initial phase of gamma-ray burst afterglows, we suggest a model for a blast wave with an intermittent energy supply. We treat the blast wave as a two-element structure. The central engine supplies energy to the inner part (shocked ejecta material) via the reverse shock. As the shocked ejecta material expands, its internal energy is transferred to the shocked external matter. We take into account the inertia of the shocked external material so that the pressure difference across this region determines the derivative of the blast wave's Lorentz factor. Applied to GRB 221009A, the model yields a very good fit to the observations of the entire TeV light curve except for three regions where there are excesses in the data with respect to the model. Those are well correlated with the three largest episodes of the prompt activity and thus, we interpret them as the reverse shock emission. Our best-fitting solution for GRB 221009A is an extremely narrow jet with an opening angle θ j ≈ 0.07° (500/Γ0) propagating into a wind-like external medium. This extremely narrow angle is consistent with the huge isotropic equivalent energy of this burst, and its inverse jet break explains the very rapid rise of the afterglow. Such inverse jet break occurs in an accelerating blast wave when the relativistic beaming becomes narrower than the jet's opening angle. Interestingly, photon–photon annihilation does not play a decisive role in the best-fitting model. [ABSTRACT FROM AUTHOR]

GRB 230812B is a bright and relatively nearby (z = 0.36) long gamma-ray burst (GRB) that has generated significant interest in the community and has thus been observed over the entire electromagnetic spectrum. We report over 80 observations in X-ray, ultraviolet, optical, infrared, and submillimetre bands from the GRANDMA (Global Rapid Advanced Network for Multimessenger Addicts) network of observatories and from observational partners. Adding complementary data from the literature, we then derive essential physical parameters associated with the ejecta and external properties (i.e. the geometry and environment) of the GRB and compare with other analyses of this event. We spectroscopically confirm the presence of an associated supernova, SN2023pel, and we derive a photospheric expansion velocity of v ∼ 17 × 103 km s−1. We analyse the photometric data first using empirical fits of the flux and then with full Bayesian inference. We again strongly establish the presence of a supernova in the data, with a maximum (pseudo-)bolometric luminosity of 5.75 × 1042 erg s−1, at |$15.76^{+0.81}_{-1.21}$|  d (in the observer frame) after the trigger, with a half-max time width of 22.0 d. We compare these values with those of SN1998bw, SN2006aj, and SN2013dx. Our best-fitting model favours a very low density environment (⁠|$\log _{10}({n_{\rm ISM}/{\rm cm}^{-3}}) = -2.38^{+1.45}_{-1.60}$|⁠) and small values for the jet's core angle |$\theta _{\rm core} = 1.54^{+1.02}_{-0.81} \ \rm {deg}$| and viewing angle |$\theta _{\rm obs} = 0.76^{+1.29}_{-0.76} \ \rm {deg}$|⁠. GRB 230812B is thus one of the best observed afterglows with a distinctive supernova bump. [ABSTRACT FROM AUTHOR]

The properties of the progenitors of gamma-ray bursts and of their environment are encoded in their luminosity function and cosmic formation rate. They are usually recovered from a flux-limited sample based on Lynden-Bell's |$c^{-}$| method. However, this method is based on the assumption that the luminosity is independent of the redshift. Observationally, if correlated, people use non-parametric |$\tau$| statistical method to remove this correlation through the transformation, |$L^{\prime }=L/g(z)$|⁠ , where z is the burst redshift, and |$g(z)=(1+z)^{k}$| parametrizes the underlying luminosity evolution. However, the application of this method to different observations could result in very different luminosity functions. By the means of Monte Carlo simulation, in this paper, we demonstrate that the origin of an observed correlation, measured by the |$\tau$| statistical method, is a complex combination of multiple factors when the underlying data are correlated. Thus, in this case, it is difficult to unbiasedly reconstruct the underlying population distribution from a truncated sample, unless the detailed information of the intrinsic correlation is accurately known in advance. In addition, we argue that an intrinsic correlation between luminosity function and formation rate is unlikely eliminated by a misconfigured transformation, and the |$g(z)$|⁠ , derived from a truncated sample with the |$\tau$| statistical method, does not necessarily represent its underlying luminosity evolution. [ABSTRACT FROM AUTHOR]

In previous studies, the time evolution information is missed in deducing the time-integrated polarizations of gamma-ray burst prompt emission. Here, it is considered and the time-integrated polarizations is investigated through the summation of the time-resolved ones. The statistical properties of the distribution of the time-integrated polarization degree (Π) can be read from the q– Π curve, where q ≡ θ V /θ j . θ V and θ j are the observational and jet half-opening angles, respectively. Hence, only the q– Π curves are studied. In addition to a toroidal magnetic field in the radiation region, an aligned field is also discussed. We found the predicted time-integrated polarization degree is around |$(40\!-\!50)\,\, \mathrm{ per\,cent}$| for High-energy Polarimetry Detector (HPD) onboard POLAR-2 and is roughly |$(30\!-\!40)\,\, \mathrm{ per\,cent}$| for its Low-energy Polarimetry Detector (LPD). Therefore, Π value detected by the HPD will be larger than that of the LPD in statistics and the result of the former estimations will underestimate the value of Π in an ordered field. There are mainly two types of the q –Π curve profiles, corresponding to two ordered magnetic field configurations. [ABSTRACT FROM AUTHOR]

The discovery of the radioactively powered kilonova AT2017gfo, associated with the short-duration gamma-ray burst GRB 170817A and the gravitational wave source GW170817, has provided the first direct evidence supporting binary neutron star mergers as crucial astrophysical sites for the synthesis of heavy elements beyond iron through r -process nucleosysthesis in the universe. However, recent identification of kilonovae following long-duration gamma-ray bursts, such as GRB 211211A and GRB 230307A, has sparked discussions about the potential of neutron star–white dwarf mergers to also produce neutron-rich ejecta and contribute to the production of heavy r -process elements. In this work, we estimate the contribution of binary neutron star mergers to the total mass of r -process elements in the Milky Way and investigate the possibility of neutron star–white dwarf mergers as alternative astrophysical sites for r -process nucleosynthesis through an analysis of the total mass of the r -process elements in the Milky Way. Our results reveal that binary neutron star mergers can sufficiently account for the Galactic heavy r -process elements, suggesting that these events are the dominant contributor to the production of heavy r -process elements in the Milky Way. Considering the total mass of r -process elements in the Milky Way and the higher occurrence rate of neutron star–white dwarf mergers, it is unlikely that such mergers can produce a significant amount of neutron-rich ejecta, with the generated mass of r -process elements being lower than |$0.005\, {\rm M}_{\odot }$|⁠. [ABSTRACT FROM AUTHOR]

Since their first discovery in the late 1960s, gamma-ray bursts have attracted an exponentially growing interest from the international community due to their central role in the most highly debated open questions of the modern research of astronomy, astrophysics, cosmology, and fundamental physics. These range from the intimate nuclear composition of high-density material within the core of ultra-dense neuron stars, to stellar evolution via the collapse of massive stars, the production and propagation of gravitational waves, as well as the exploration of the early universe by unveiling the first stars and galaxies (assessing also their evolution and cosmic re-ionization). GRBs in the past ∼50 years have stimulated the development of cutting-edge technological instruments for observations of high-energy celestial sources from space, leading to the launch and successful operations of many different scientific missions (several of them still in data-taking mode currently). In this review, we provide a brief description of the GRB-dedicated missions from space being designed and developed for the future. The list of these projects, not meant to be exhaustive, shall serve as a reference to interested readers to understand what is likely to come next to lead the further development of GRB research and the associated phenomenology. [ABSTRACT FROM AUTHOR]

According to the hypothesis that strange quark matter may be the true ground state of matter at extremely high densities, strange quark stars should be stable and could exist in the Universe. It is possible that pulsars may actually be strange stars, but not neutron stars. Here we present a short review on recent progresses in the field of strange quark stars. First, three popular phenomenological models widely used to describe strange quark matter are introduced, with special attention being paid on the corresponding equation of state in each model. Combining the equation of state with the Tolman-Oppenheimer-Volkov equations, the inner structure and mass-radius relation can be obtained for the whole sequence of strange stars. Tidal deformability and oscillations (both radial and non-radial oscillations), which are sensitive to the composition and the equations of state, are then described. Hybrid stars as a special kind of quark stars are discussed. Several other interesting aspects of strange stars are also included. For example, strong gravitational wave emissions may be generated by strange stars through various mechanisms, which may help identify strange stars via observations. Especially, close-in strange quark planets with respect to their hosts may provide a unique test for the existence of strange quark objects. Fierce electromagnetic bursts could also be generated by strange stars. The energy may come from the phase transition of neutron stars to strange stars, or from the merger of binary strange stars. The collapse of the strange star crust can also release a huge amount of energy. It is shown that strange quark stars may be involved in short gamma-ray bursts and fast radio bursts.

Based on different neutron star–white dwarf (NS–WD) population models, we investigate the prospects of gravitational-wave (GW) detections for NS–WD mergers, with the help of early warnings from two space-borne decihertz GW observatories, DO-Optimal and DECIGO. We not only give quick assessments of the GW detection rates for NS–WD mergers with the two decihertz GW detectors, but also report systematic analyses on the characteristics of GW-detectable merger events using the method of Fisher matrix. With a sufficient 1-d early-warning time, the yearly GW detection number for DO-Optimal is in the range of (1.5–1.9) × 103, while it is (3.3–4.6) × 104 for DECIGO. More importantly, our results show that most NS–WD mergers can be localized with an uncertainty of |$\mathcal {O}(10^{-2})\, \mathrm{deg}^2$|⁠. Given the NS–WD merger as a possible origin for a peculiar long-duration gamma-ray burst, GRB 211211A, followed with kilonova-like emissions, we further suggest that the GW early-warning detection would allow future electromagnetic telescopes to get prepared to follow up transients after some special NS–WD mergers. Based on our analyses, we emphasize that such a feasible 'wait-for' pattern can help to firmly identify the origin of GRB 211211A-like events in the future and bring excellent opportunities for the multimessenger astronomy. [ABSTRACT FROM AUTHOR]

We present counts-level fits to the multi-instrument (keV–GeV) data of the early afterglow (4 ks, 22 ks) of the brightest gamma-ray burst detected to date, GRB 221009A. The complexity of the data reduction, due to the unprecedented brightness and the location in the Galactic plane, is critically addressed. The energy spectrum is found to be well described by a smoothly broken power law with a break energy at a few keV. Three interpretations (slow/fast cooling or the transition between these) within the framework of forward shock synchrotron emission, from accelerated and subsequently cooled electrons, are found. The physical implications for each of these scenarios are discussed. [ABSTRACT FROM AUTHOR]

GW170817 is a binary neutron star merger that exhibited a gravitational wave (GW) and a gamma-ray burst, followed by an afterglow. In this work, we estimate the Hubble constant (H 0) using broad-band afterglow emission and relativistic jet motion from the Very Long Baseline Interferometry and HST images of GW170817. Compared to previous attempts, we combine these messengers with GW in a simultaneous Bayesian fit. We probe the H 0 measurement robustness depending on the data set used, the assumed jet model, the possible presence of a late time flux excess. Using the sole GW leads to a 20 per cent error (⁠|$77^{+21}_{-10}$|   |$\rm km\, s^{-1}\, Mpc^{-1}$|⁠ , medians, 16th–84th percentiles), because of the degeneracy between viewing angle (θv) and luminosity distance (d L). The latter is reduced by the inclusion in the fit of the afterglow light curve, leading to |$H_0=96^{+13}_{-10}$|   |$\rm km\, s^{-1}\, Mpc^{-1}$|⁠ , a large value, caused by the fit preference for high viewing angles due to the possible presence of a late-time excess in the afterglow flux. Accounting for the latter by including a constant flux component at late times brings |$H_0=78.5^{+7.9}_{-6.4}$| |$\rm km\, s^{-1}\, Mpc^{-1}$|⁠. Adding the centroid motion in the analysis efficiently breaks, the d L − θv degeneracy and overcome the late-time deviations, giving |$H_0 = 69.0^{+4.4}_{-4.3}$|   |$\rm km\, s^{-1}\, Mpc^{-1}$| (in agreement with Planck and SH0ES measurements) and |$\theta _{\rm v} = 18.2^{+1.2}_{-1.5}$| °. This is valid regardless of the jet structure assumption. Our simulations show that for next GW runs radio observations are expected to provide at most few other similar events. [ABSTRACT FROM AUTHOR]

Emission in many astrophysical transients originates from a shocked fluid. A central engine typically produces an outflow with varying speeds, leading to internal collisions within the outflow at finite distances from the source. Each such collision produces a pair of forward and reverse shocks with the two shocked regions separated by a contact discontinuity (CD). As a useful approximation, we consider the head-on collision between two cold and uniform shells (a slower leading shell and a faster trailing shell) of finite radial width, and study the dynamics of shock propagation in planar geometry. We find significant differences between the forward and reverse shocks, in terms of their strength, internal energy production efficiency, and the time it takes for the shocks to sweep through the respective shells. We consider the subsequent propagation of rarefaction waves in the shocked regions and explore the cases where these waves can catch up with the shock fronts and thereby limit the internal energy dissipation. We demonstrate the importance of energy transfer from the trailing to leading shell through p d V work across the CD. We outline the parameter space regions relevant for models of different transients,e.g. Gamma-ray burst internal shock model, fast radio burst blast wave model, Giant flare due to magnetars, and superluminous supernovae ejecta. We find that the reverse shock likely dominates the internal energy production for many astrophysical transients. [ABSTRACT FROM AUTHOR]

The discovery of a short gamma‐ray burst (GRB), GRB170817A, in association with a gravitational wave (GW) and a bright kilonova started a new era in the high‐energy astrophysics. The observation of GRB170817A and more recently, GRB200826A and GRB211211A, a short and a long burst, respectively, with a possible kilonova, reinforce the concern about new ways of classification. For this reason, a new machine learning technique is applied to Swift‐BAT data, searching for morphological similarities in the light curves. The resulting map is characterized by two distinct groups, although still correlated with standard T90 duration. Since a jet viewed off‐axis could explain the emission from GRB170817A, the modeling of this kind of sources is of great importance. A public code called JetFit, based on the "boosted fireball" model, is applied to fit Swift‐XRT afterglow light curves of short and long GRBs, with known red‐shift, from 2005 to 2021. JetFit does not model the flaring activity. For this purpose, a new technique to remove the time flaring phases, is developed. This analysis provides a comprehensive study of the prompt and of the afterglow phase, trough the study of the best‐fit parameters. [ABSTRACT FROM AUTHOR]

Gamma-ray bursts (GRBs) comprise short, bright, energetic flashes of emission from extragalactic sources followed by a longer afterglow phase of decreased brightness. Recent discoveries of very high energy (VHE, ≳100 GeV) afterglow emission from GRB 180720B and GRB 190829A by the High Energy Stereoscopic System have raised questions regarding the emission mechanism responsible. We interpret this observed late-time emission to be the result of inverse Compton emission of ultrarelativistic electrons in the GRB blast wave in an external radiation field, i.e. external Compton (EC), considering both the wind and interstellar medium scenarios. We present predictions of multiwavelength light curves and energy spectra, ranging from optical to VHE, and include the synchrotron and synchrotron self-Compton (SSC) radiation mechanisms as well. We corrected the EC and SSC models for the gamma-ray attenuation by absorption of photons through their interaction with the extragalactic background light. We compared our results to multiwavelength data and found that EC gives a satisfactory fit for a given set of fixed model parameters for GRB 180720B, whereas SSC results in a better fit for GRB 190829A. For both GRBs, a wind environment is preferred over constant-density interstellar medium, and the cosmic microwave background as the external radiation field. However, with more data and an effective optimization tool we can find a more robust fit of the model, implying better constraints on the GRB environment and the particle energy requirements for the emission observed at late times. This has consequences for future observations of GRBs at these extreme energies. [ABSTRACT FROM AUTHOR]

We present full photometric coverage and spectroscopic data for soft gamma-ray burst GRB 201015A with a redshift z = 0.426. Our data span a time range of 85 d following the detection of GRB. These observations revealed an underlying supernova SN 201015A with a maximum at 8.54 ± 1.48 d (rest frame) and an optical peak absolute magnitude |$-19.45_{-0.47}^{+0.85}$| mag. The SN stands out clearly, since the contribution of the afterglow at this time is not dominant, which made it possible to determine SN's parameters. A comparison of these parameters reveals that the SN 201015A is the earliest (the minimum T max) known SN associated with GRBs. Spectroscopic observations during the SN decay stage showed broad lines, indicating a large photospheric velocity, and identified this SN as a Type Ic-BL. Thus, the SN 201015A associated with the GRB 201015A becomes the 27th SN/GRB confirmed by both photometric and spectroscopic observations. Using the results of spectral analysis based on the available data of Fermi -GBM experiment, the parameters E p,i = 20.0 ± 8.5 keV and E iso = (1.1 ± 0.2) × 1050 erg were obtained. According to the position of the burst on the E p,i– E iso correlation, GRB 201015A was classified as a type II (long) GRB, which was also confirmed by the T 90,i– EH diagram. [ABSTRACT FROM AUTHOR]

We have constructed a model for the passage of gamma-ray burst radiation through a dense molecular cloud. In our calculations we take into account the main radiation–cloud material interaction processes: the ionization of H and He atoms, the ionization of metal ions with the emission of Auger electrons, the ionization and photodissociation of H molecules, the absorption of ultraviolet radiation in the H lines of the Lyman and Werner bands, and the vaporization of dust grains. The ionization of metal ions by X-ray radiation determines the gas ionization fraction in the region where the gas is predominantly neutral. The photoionization of the inner electron shells of ions is accompanied by the emission of Auger electrons, giving rise to metal ions in a high ionization state. In particular, the column densities of Mg, Si, and Fe ions in the ionization states I–IV are much lower than the column densities of these ions in the ionization state V or higher. The photoionization of metal ions by ultraviolet radiation occurs only at distances smaller than the dust vaporization radius and for neutral atoms with an ionization threshold below 13.6 eV. The results of our calculations have confirmed the previously made assumption that the ionization of He atoms plays an important role in the absorption of radiation in the X-ray wavelength range. For a low metallicity, , the role of helium atoms is dominant. [ABSTRACT FROM AUTHOR]

The Hubble tension in cosmology is not showing signs of alleviation and thus, it is important to look for alternative approaches to it. One such example would be the eventual detection of a time delay between simultaneously emitted high-energy and low-energy photons in gamma-ray bursts (GRB). This would signal a possible Lorentz Invariance Violation (LIV) and in the case of non-zero quantum gravity time delay, it can be used to study cosmology as well. In this work, we use various astrophysical datasets (BAO, Pantheon Plus and the CMB distance priors), combined with two GRB time delay datasets with their respective models for the intrinsic time delay. Since the intrinsic time delay is considered the largest source of uncertainty in such studies, finding a better model is important. Our results yield as quantum gravity energy bound E Q G ≥ 10 17 GeV and E Q G ≥ 10 18 GeV respectively. The difference between standard approximation (constant intrinsic lag) and the extended (non-constant) approximations is minimal in most cases we conside. However, the biggest effect on the results comes from the prior on the parameter c H 0 r d , emphasizing once again that at current precision, cosmological datasets are the dominant factor in determining the cosmology. We estimate the energies at which cosmology gets significantly affected by the time delay dataset. [ABSTRACT FROM AUTHOR]

This is the first in a collection of three papers introducing the science with an ultra-violet (UV) space telescope on an approximately 130 kg small satellite with a moderately fast re-pointing capability and a real-time alert communication system approved for a Czech national space mission. The mission, called Quick Ultra-Violet Kilonova surveyor—QUVIK, will provide key follow-up capabilities to increase the discovery potential of gravitational wave observatories and future wide-field multi-wavelength surveys. The primary objective of the mission is the measurement of the UV brightness evolution of kilonovae, resulting from mergers of neutron stars, to distinguish between different explosion scenarios. The mission, which is designed to be complementary to the Ultraviolet Transient Astronomy Satellite—ULTRASAT, will also provide unique follow-up capabilities for other transients both in the near- and far-UV bands. Between the observations of transients, the satellite will target other objects described in this collection of papers, which demonstrates that a small and relatively affordable dedicated UV-space telescope can be transformative for many fields of astrophysics. [ABSTRACT FROM AUTHOR]

A state-of-the-art semi-analytic gamma-ray burst (GRB) afterglow model with synchrotron self-Compton (SSC) emission has been applied for the first time for parameter inference using real GRB data. We analyzed the famous GRB 190114C as a case study. GRB 190114C, characterized by its long duration and high luminosity, was observed by many ground-based and orbiting telescopes spanning a wide range of electromagnetic wavelengths, from radio to GeV gamma rays. We used two advanced algorithms for inference: a nested sampling algorithm called UltraNest and an MCMC algorithm emcee. Evoking the standard afterglow model, the inference result and the best-fit values lead to an initial bulk Lorentz factor (a rough estimate of Γ = 526 ), which aligns with the values often seen in GRBs identified by the Fermi-LAT instrument. Similarly to the best-fit values of other studies in the literature, the derived values of microphysical parameters, the circumburst density, and the kinetic efficiency are consistent with those found after modeling the multi-wavelength observations in GRB 190114C. We show that the SSC from the forward-shock region can only describe the highest-energy photons above a few GeVs. [ABSTRACT FROM AUTHOR]

One of the possible resolutions of the compactness problem in gamma-ray bursts (GRBs) is by invoking the Lorentz factors associated with the relativistic bulk motion. This model applies to GRBs where sufficient energy is converted to accelerate the ejected matter to relativistic speeds. In some situations, this may not be a possible mechanism, and as a result, the gamma rays are trapped in the region. In this work, we look at such possible scenarios and where the neutrino pair production process can dominate. As a result, the neutrinos can escape freely. This could give rise to a scenario where the release of neutrinos precedes the gamma-ray emission that is much attenuated. This model can thus possibly explain why fewer GRBs are observed than what is expected. [ABSTRACT FROM AUTHOR]

We explore large-scale cosmic structure using the spatial distribution of 542 gamma-ray bursts (GRBs) having accurately measured positions and spectroscopic redshifts. Prominent cosmological clusters are identified in both the northern and southern galactic hemispheres (avoiding extinction effects in the plane of the Milky Way) using the bootstrap point-radius method. The northern galactic hemisphere contains a significant group of four GRBs in the redshift range 0.59 ≤ z ≤ 0.62 (with a bootstrap probability of p  = 0.012) along with the previously identified Hercules–Corona Borealis Great Wall (in the revised redshift range 0.9 ≤ z ≤ 2.1; p  = 0.017). The southern galactic hemisphere contains the previously identified Giant GRB Ring (p  = 0.022) along with another possible cluster of seven to nine GRBs at 1.17 ≤ z ≤ 1.444 (p  = 0.031). Additionally, both the Hercules–Corona Borealis Great Wall and the Giant GRB Ring have become more prominent as the GRB sample size has grown. The approach used here underscores the potential value of GRB clustering as a probe of large-scale cosmic structure, complementary to galaxy and quasar clustering. Because of the vast scale on which GRB clustering provides valuable insights, it is important that optical GRB monitoring continues so that additional spectroscopic redshift measurements could be obtained. [ABSTRACT FROM AUTHOR]

Gamma-ray burst (GRB) afterglow light curves and spectra provide information about the density of the environment, the energy of the explosion, the properties of the particle acceleration process, and the structure of the decelerating jet. Due to the large number of parameters involved, the model can present a certain degree of parameter degeneracy. In this paper, we generated synthetic photometric data points using a standard GRB afterglow model and fit them using the Markov chain Monte Carlo (MCMC) method. This method has emerged as the preferred approach for analysing and interpreting data in astronomy. We show that, depending on the choice of priors, the parameter degeneracy can go unnoticed by the MCMC method. Furthermore, we apply the MCMC method to analyse the GRB 170817A afterglow. We find that there is a complete degeneracy between the energy of the explosion E , the density of the environment n , and the microphysical parameters describing the particle acceleration process (e.g. ϵ e and ϵ B ), which cannot be determined by the afterglow light curve alone. Our results emphasize the importance of gaining a deep understanding of the degeneracy properties which can be present in GRB afterglows models, as well as the limitations of the MCMC method. In the case of GRB 170817, we get the following values for the physical parameters: E  = 8 × 1050–1 × 1053 erg, n  = 7 × 10−5–9 × 10−3, ϵ e  = 10−3–0.3, ϵ B  = 10−10–0.3. [ABSTRACT FROM AUTHOR]

In some cases, the merger of two neutron stars can produce a rapidly rotating and highly magnetized millisecond magnetar. A significant proportion of the rotational energy deposited to the emerging ejecta can produce a late-time radio brightening from interacting with the ambient medium. Detection of this late-time radio emission from short GRBs can have profound implications for understanding the physics of the progenitor. We report the radio observations of five short GRBs – 050709, 061210, 100625A, 140903A, and 160821B using the legacy Giant Metrewave Radio Telescope (GMRT) at 1250, 610, and 325 MHz frequencies and the upgraded-GMRT (uGMRT) at band 5 (1050–1450 MHz) and band 4 (550–900 MHz) after ∼2–11 yr from the time of the burst. The GMRT observations at low frequencies are particularly important to detect the signature of merger ejecta emission at the peak. These observations are the most delayed searches associated with some GRBs for any late-time low-frequency emission. We find no evidence for such an emission. We find that none of these GRBs is consistent with maximally rotating magnetar with a rotational energy of |$\sim 10^{53}\, {\rm erg}$|⁠. However, magnetars with lower rotational energies cannot be completely ruled out. Despite the non-detection, our study underscores the power of radio observations in the search for magnetar signatures associated with short GRBs. However, only future radio observatories may be able to detect these signatures or put more stringent constraints on the model. [ABSTRACT FROM AUTHOR]

Precursors have been observed seconds to minutes before some short gamma-ray bursts. While the precursor origins remain unknown, one explanation relies on the resonance of neutron star pulsational modes with the tidal forces during the inspiral phase of a compact binary merger. In this paper, we present a model for short gamma-ray burst precursors that relies on tidally resonant neutron star oceans. In this scenario, the onset of tidal resonance in the crust–ocean interface mode ignites the precursor flare, possibly through the interaction between the excited neutron star ocean and the surface magnetic fields. From just the precursor total energy, the time before the main event, and a detected quasi-periodic oscillation frequency, we may constrain the binary parameters and neutron star ocean properties. Our model can immediately distinguish neutron star–black hole mergers from binary neutron star mergers without gravitational wave detection. We apply our model to GRB 211211A, the recently detected long duration short gamma-ray burst with a quasi-periodic precursor, and explore the parameters of this system. The precursor of GRB 211211A is consistent with a tidally resonant neutron star ocean explanation that requires an extreme mass ratio neutron star–black hole merger and a high-mass neutron star. While difficult to reconcile with the main gamma-ray burst and associated kilonova, our results constrain the possible precursor mechanisms in this system. A systematic study of short gamma-ray burst precursors with the model presented here can test precursor origin and probe the possible connection between gamma-ray bursts and neutron star–black hole mergers. [ABSTRACT FROM AUTHOR]

Gamma-ray bursts (GRBs) are explosive transient events occurring at cosmological distances, releasing a large amount of energy as electromagnetic radiation over several energy bands. We report the detection of the long GRB 201216C by the MAGIC telescopes. The source is located at z  = 1.1 and thus it is the farthest one detected at very high energies. The emission above 70 GeV of GRB 201216C is modelled together with multiwavelength data within a synchrotron and synchrotron self-Compton (SSC) scenario. We find that SSC can explain the broad-band data well from the optical to the very-high-energy band. For the late-time radio data, a different component is needed to account for the observed emission. Differently from previous GRBs detected in the very-high-energy range, the model for GRB 201216C strongly favours a wind-like medium. The model parameters have values similar to those found in past studies of the afterglows of GRBs detected up to GeV energies. [ABSTRACT FROM AUTHOR]

We have received a new physical characteristics fitting based on actual observational data from the Swift mission's long-duration gamma-ray bursts (LGRBs). We considered such characteristics as the Amati parameters for linear correlation (E iso– E p, i ) and the k -correction for gravitational lensing and Malmquist bias (GLMB) effect. We used the Pantheon SN Ia catalogue and the standard Lambda cold dark matter model with a fixed Hubble constant of H 0 = 70 km s−1 Mpc−1 as the baseline for the Hubble function μ(z). In our paper, we formulated the inverse cosmological calibration problem (ICCP) in the non-parametric statistics framework. The ICCP involves fitting non-observable physical characteristics while assuming a fixed cosmological model. To solve this problem, we developed a new method that is resistant to non-Gaussian processes. This method is based on error propagation through the Monte Carlo method and the Theil–Sen method for linear regression estimate. We have demonstrated the stability and robustness of this assessment method. The parameter estimates are as follows: |$a=0.92^{+0.12}_{-0.12}$|⁠ , |$b=50.32^{+0.33}_{-0.32}$| without considering the GLMB effect, and |$a=0.63^{+0.13}_{-0.14}$|⁠ , |$b=50.12^{+0.33}_{-0.31}$|⁠ , and |$k=1.98^{+0.25}_{-0.24}$| with the effect included. The proposed method can be applied to any other calibration sample of known standard candles, a calibrated sample of LGRBs, and the Hubble function μ(z). In the future, the ICCP idea can be used as an alternative cosmological test for estimating cosmological parameters, including the GLMB effect, or even for the selection of models, providing new information about the Universe. This can be done by analysing the residual values of observational data within the Bayesian statistics paradigm. [ABSTRACT FROM AUTHOR]

The results of a study of the short gamma-ray burst GRB 231115A in the X-ray and gamma-ray ranges are presented, based on data from the INTEGRAL and Fermi space observatories. The source of the burst is localized by the IBIS/ISGRI telescope of INTEGRAL observatory with an accuracy of , it is located in the Cigar Galaxy (M 82). Early follow-up observations of the burst localization region were carried out in the optical range with the 36-cm telescope of the ISON-Kitab observatory and the 70-cm telescope AS-32 of the Abastumani Astrophysical Observatory. The optical emission has not been detected. The proximity of the host galaxy ( Mpc) significantly limits energetics of the event ( erg) and allows us to interpret the burst as a giant flare of a previously unknown soft gamma repeater (SGR) which is an extreme manifestation of the activity of a highly magnetized neutron star (magnetar). This conclusion is confirmed by the energy spectrum atypically hard for cosmological gamma-ray bursts, as well as the absence of optical afterglow and gravitational wave signal, which should have been detected in the LIGO/Virgo/KAGRA experiments if the burst was caused by a merger of binary neutron stars. The location of the burst in the and diagrams also suggests that GRB 231115A was a magnetar giant flare. This is the first well-localized giant flare of an extragalactic SGR. [ABSTRACT FROM AUTHOR]

Before the Neil Gehrels Swift Observatory, we knew little about short-duration Gamma-ray bursts (sGRBs). Their briefness led to the suspicion that they resulted from mergers of compact objects, e.g., two neutron stars or a neutron star and a black hole. However, proof was lacking. sGRB post-prompt emission, or afterglow, was undetected; thus, we could not apply essential investigation tools. Swift was the first to pinpoint sGRB afterglows. sGRBs were found to differ from long GRBs in terms of host galaxies, offset from host, environment, energy and progenitors. The Swift UV/Optical Telescope (UVOT) has greatly contributed to these discoveries with its unique combination of fast repointing capabilities and UV sensitivity. But the long-sought proof of the sGRB–merger connection arrived in 2017. The gravitational signal GW 170817A caused by two NSs collision was associated with sGRB 170817A. Swift/UVOT discovered that its early optical emission was—unusually for GRB afterglows—thermal. It was interpreted as an emission from the merger's hot debris: the kilonova. Kilonovae have seemingly been found in other sGRBs and—puzzingly—in long GRBs. Over almost 20 years, Swift/UVOT observations have also been pivotal to understanding peculiar events. In this review, I will summarize UVOT's major contributions in the fields highlighted. [ABSTRACT FROM AUTHOR]

Neutron star mergers are astrophysical “gold mines,” synthesizing over half of the elements heavier than iron through rapid neutron capture nucleosynthesis. The observation of the binary neutron star merger GW170817, detected both in gravitational waves and electromagnetic radiation, marked a breakthrough. One electromagnetic component of this event, the gamma ray burst GRB 170817A, has an unresolved aspect: the characteristics of its prompt gamma-ray emission spectrum. In this work, we investigate that gamma-ray spectra in such GRBs may be influenced by de-excitations from isomeric transitions. Our study begins with a review of current knowledge on GRB structure and of r-process nucleosynthesis in neutron star collisions, focusing on the role of nuclear isomers in these settings. We then test our hypothesis by developing criteria to select representative isomers, based on known solar element abundances, for modeling GRB spectral characteristics. We integrate these criteria into an interactive web page, facilitating the construction and analysis of relevant gamma-ray spectra from isomeric transitions. Our analysis reveals that three isomers—90Zr, 207Pb, and 89Y—stand out for their potential to impact the prompt GRB spectrum due to their specific properties. This information allows us to incorporate nuclear isomer data into astrophysical simulations and calculate isomeric abundances generated by astrophysical r-processes in neutron star mergers and their imprint on the detected signal.

The stellar initial mass function (IMF) represents a fundamental quantity in astrophysics and cosmology describing the mass distribution of stars from low mass all the way up to massive and very massive stars. It is intimately linked to a wide variety of topics, including stellar and binary evolution, galaxy evolution, chemical enrichment, and cosmological reionization. Nonetheless, the IMF still remains highly uncertain. In this work, we aim to determine the IMF with a novel approach based on the observed rates of transients of stellar origin. We parametrize the IMF with a simple but flexible Larson shape, and insert it into a parametric model for the cosmic UV luminosity density, local stellar mass density, type Ia supernova (SN Ia), core-collapse supernova (CCSN), and long gamma-ray burst (LGRB) rates as a function of redshift. We constrain our free parameters by matching the model predictions to a set of empirical determinations for the corresponding quantities via a Bayesian Markov Chain Monte Carlo method. Remarkably, we are able to provide an independent IMF determination with a characteristic mass mc=0.10−0.08+0.24M⊙ and high-mass slope ξ=−2.53−0.27+0.24 that are in accordance with the widely used IMF parameterizations (e.g., Salpeter, Kroupa, Chabrier). Moreover, the adoption of an up-to-date recipe for the cosmic metallicity evolution allows us to constrain the maximum metallicity of LGRB progenitors to Zmax=0.12−0.05+0.29Z⊙. We also find which progenitor fraction actually leads to SN Ia or LGRB emission (e.g., due to binary interaction or jet-launching conditions), put constraints on the CCSN and LGRB progenitor mass ranges, and test the IMF universality. These results show the potential of this kind of approach for studying the IMF, its putative evolution with the galactic environment and cosmic history, and the properties of SN Ia, CCSN, and LGRB progenitors, especially considering the wealth of data incoming in the future.

Gamma-ray bursts (GRBs) are intense and short-lived cosmic explosions. Miniaturised CubeSat-compatible instruments for the study of GRBs are being developed to help bridge the gap in large missions and assist in achieving full sky coverage. CubeSats are small, compact satellites conforming to a design standard and have transformed the space industry. They are relatively low-cost and are developed on fast timescales, which has provided unparalleled access to space. This paper focuses on GMOD, the gamma-ray module, onboard the 2U CubeSat EIRSAT-1, launched on December 1st 2023. GMOD is a scintillation-based instrument with a cerium bromide crystal coupled to an array of sixteen silicon photomultipliers, designed for the detection of GRBs. The characterisation of GMOD in the spacecraft, along with the validation of an updated spacecraft MEGAlib model is presented and this approach can be followed by other CubeSats with similar science goals. The energy resolution of the flight model is 7.07% at 662 keV and the effective area peaks in the tens to hundreds of keV, making it a suitable instrument for the detection of GRBs. An investigation into the instrument’s angular response is also detailed. The results from this characterisation campaign are a benchmark for the instrument’s performance pre-launch and will be used to compare with the detector’s performance in orbit.

We investigate the impact of forthcoming nuclear data on the predictions of the neutron star (NS) stripping model for short gamma-ray bursts. The main area to which we pay attention is the NS crust. We show that the uncertain properties of the NS equation of state can significantly influence the stripping time tstr, the main dynamical parameter of the model. Based on the known time delay (tstr≈1.7 s) between the peak of the gravitational wave signal GW170817 and the detection of gamma photons from GRB170817A, we obtain new restrictions on the nuclear matter parameters, in particular, the symmetry energy slope parameter: L<114.5MeV. In addition, we study the process of nucleosynthesis in the outer and inner crusts of a low-mass NS. We show that the nucleosynthesis is strongly influenced by both the forthcoming nuclear data and the equation of state of the NS matter.

Thanks to the rapidly increasing time-domain facilities, we are entering a golden era of research on gamma-ray bursts (GRBs). In this Letter, we report our observations of GRB 240529A with the Burst Optical Observer and Transient Exploring System, the 1.5 m telescope at Observatorio de Sierra Nevada, the 2.5 m Wide Field Survey Telescope of China, the Large Binocular Telescope, and the Telescopio Nazionale Galileo. The prompt emission of GRB 240529A shows two comparable energetic episodes separated by a quiescence time of roughly 400 s. Combining all available data on the GRB Coordinates Network, we reveal the simultaneous apparent X-ray plateau and optical rebrightening around 10 ^3 –10 ^4 s after the burst. Rather than the energy injection from the magnetar as widely invoked for similar GRBs, the multiwavelength emissions could be better explained as two shocks launched from the central engine separately. The optical peak time and our numerical modeling suggest that the initial bulk Lorentz factor of the later shock is roughly 50, which indicates that the later jet should be accretion driven and have a higher mass loading than a typical one. The quiescence time between the two prompt emission episodes may be caused by the transition between different accretion states of a central magnetar or black hole, or the fallback accretion process. A sample of similar bursts with multiple emission episodes in the prompt phase and sufficient follow-up could help to probe the underlying physics of GRB central engines.