Gamma-ray Bursts Research Articles

Capability of Searching for Kilonova Associated with a Short Gamma-Ray Burst by SVOM

In spite of the importance of studying the cosmic generation of heavy elements through the r-process, the detection of a kilonova resulting from the merger of a neutron star binary is still a challenging task. In this paper, we show that the Visible Telescope (VT) onboard the ongoing SVOM space mission is powerful for identifying kilonova candidates associated with short gamma-ray bursts up to a distance of 600 Mpc. A significant color variation, turning blue and then turning red, is revealed by calculating the light curves in both red and blue channels of VT by a linear combination of an afterglow and an associated kilonova. The maximum color variation is as high as ∼0.5–1 mag, which is far larger than the small photometry error of ∼0.2 mag of VT for a point source with a brightness of 23 mag. Up to a distance of 600 Mpc, ∼1–2 kilonova candidates per year are predicted to be identified by VT.

Evolution of the Universe with quintessence model in Rastall gravity

Abstract We investigate the Universe’s evolution within the framework of Rastall gravity, which is an extension of the standard ΛCDM model. Utilizing a linear parametrization of the Equation of State (EoS) in a Friedmann-Lemaître-Robertson-Walker (FLRW) background, we constrain the model parameters through analysis of cosmic chronometers (CC), Pantheon, Gold, Gamma Ray Burst (GRB), and Baryon Acoustic Oscillations (BAO) datasets, as well as their joint analysis, under 1σ and 2σ confidence levels, considering the Rastall parameter λ. The constrained parameters are then used to compare our model with the standard ΛCDM model. Our findings include a detailed examination of the model’s physical interpretations and demonstrate the potential for an accelerating universe expansion in later times, aligning with the observed behavior of dark energy.

Modeling of Long-term Afterglow Counterparts to Gravitational Wave Events: The Full View of GRB 170817A

The arrival of gravitational wave astronomy and a growing number of time-domain-focused observatories are set to lead to an increasing number of detections of short gamma-ray bursts (GRBs) launched with a moderate inclination to Earth. Being nearby events, these are also prime candidates for very long-term follow-up campaigns and very long-baseline interferometry, which has implications for multi-messenger modeling, data analysis, and statistical inference methods applied to these sources. Here, we present a comprehensive modeling update that directly incorporates into afterglowpy astrometric observations of the GRB position, Poissonian statistics for faint sources, and modeling of a trans-relativistic population of electrons. We use the revolutionary event GW170817 to demonstrate the impact of these extensions both for the best-fit physics parameters and model selection methods that assess the statistical significance of additional late-time emission components. By including in our analysis the latest Chandra X-ray observations of GRB 170817A, we find only weak evidence (≲2σ) for a new emission component at late times, which makes for a slightly more natural fit to the centroid evolution and prediction for the external medium density.

The Early Radio Afterglow of Short GRB 230217A

We present the radio afterglow of short gamma-ray burst (GRB) 230217A, which was detected less than 1 day after the gamma-ray prompt emission with the Australia Telescope Compact Array (ATCA) and the Karl G. Jansky Very Large Array. The ATCA rapid-response system automatically triggered an observation of GRB 230217A following its detection by the Neil Gehrels Swift Observatory and began observing the event just 32 minutes postburst at 5.5 and 9 GHz for 7 hr. Dividing the 7 hr observation into three time-binned images allowed us to obtain radio detections with logarithmic central times of 1, 2.8, and 5.2 hr postburst, the first of which represents the earliest radio detection of any GRB to date. The decline of the light curve is consistent with reverse shock emission if the observing bands are below the spectral peak and not affected by synchrotron self-absorption. This makes GRB 230217A the fifth short GRB (SGRB) with radio detections attributed to a reverse shock at early times (<1 day postburst). Following brightness temperature arguments, we have used our early radio detections to place the highest minimum Lorentz factor ( Γmin>50 at ∼1 hr) constraints on a GRB in the radio band. Our results demonstrate the importance of rapid radio follow-up observations with long integrations and good sensitivity for detecting the fast-evolving radio emission from SGRBs and probing their reverse shocks.

The Scintillation Counters of the High-Energy Particle Detector of the China Seismo-Electromagnetic (CSES-02) Satellite

The High-Energy Particle Detector (HEPD-02) is one of the scientific payloads of the China Seismo-Electromagnetic Satellite (CSES-02). The HEPD-02’s main purpose is to characterize the particle environment in the Earth’s vicinity, identifying sudden changes in the fluxes and correlating them with solar and terrestrial phenomena. Additionally, HEPD-02 also has capabilities in detecting Gamma-Ray Bursts. At the core of HEPD-02, a tower of scintillation counters made of plastic and LYSO crystals is able to recognize electrons in the range between 3 and 100 MeV, protons and nuclei between 30 and 200 MeV/n. Plastic scintillators covering the calorimeter on five sides allow to reject particles entering from the top and not completely absorbed within its volume. In this work, the design of the HEPD-02 is reviewed in comparison to its predecessor, HEPD-01, highlighting the innovations of the new design. The design of each scintillation counter type has been fully validated through a campaign of prototype realization, testing, and characterization. The production of the scintillation counters, including the PMT selection process, is also discussed. Finally, the performance of the counters is compared with simulations, showing an agreement of within 20% with the expected performance, thereby meeting expectations.

Is Gamma-Ray Burst 221009A Really a Once-in-10,000 yr Event?

Gamma-ray bursts (GRBs) brighter than the GRB 221009A, the brightest yet observed, have previously been estimated to occur at a rate of one per 10,000 yr, based on the extrapolation of the distribution of fluences of the long-GRB population. We show that bursts this bright could instead have a rate as high as approximately one per 200 yr if they are from a separate population of narrow-jet GRBs. This population must have a maximum redshift of about z ≈ 0.38 in order to avoid overproducing the observed rate of fainter GRBs. We show that it will take ≳100 yr to confirm this new population based on observing another GRB from it with a γ-ray detector; observing an orphan optical afterglow from this population with Vera Rubin Observatory or an orphan radio afterglow with the Square Kilometer Array will also take similarly long times to observe, and it is unclear if they could be distinguished from the standard GRB population. We show that the nearby narrow-jet population has more favorable energetics for producing ultra-high-energy cosmic rays than standard GRBs. The rate of bursts in the Milky Way bright enough to cause mass extinctions of life on Earth from the narrow-jet population is estimated to be approximately one per 500 Myr. This GRB population could make life in the Milky Way less likely, with implications for future searches for life on exoplanets.

Robust constraints on the physics of the MeV emission line in GRB 221009A from optical depth arguments

ABSTRACT The brightest-of-all-time gamma-ray burst (GRB), GRB 221009A, is the first GRB observed to have emission line (up to 37 MeV) in its prompt emission spectra. It is naturally explained as $e^-/e^+$ annihilation line that was Doppler boosted in the relativistic jet of the GRB. In this work, we repeatedly apply the simple optical depth argument to different physical processes necessary to produce an observable $e^-/e^+$ annihilation line. This approach results in robust constraints on the physics of the line: We conclude that in GRB 221009A, the $e^-/e^+$ pairs were produced at a radius greater than $4.3\times 10^{15}$ cm from the central engine, and annihilated in a region between $1.4\times 10^{16}$ and $4.3\times 10^{16}$ cm. From these constraints, we established a self-consistent picture of $e^-/e^+$ production, cooling, and annihilation. We also derived a criterion for pair production in the GRB prompt emission: $E_{\rm {iso}} \gtrsim 3.3\times 10^{53} E_{\rm {peak},100} (1+z) R^2_{\rm {prod},16}~\text{erg}$. Using this criterion, we find tens of candidate GRBs that could have produced $e^-/e^+$ in prompt emissions to annihilate. GRB 221009A is with the highest likelihood according to this criterion. We also predict the presence of a thermal radiation, with a time-evolving blackbody temperature, sweeping through soft X-ray during the prompt emission phase.

Studies of GAGG:Ce scintillators for space missions dedicated to Terrestrial Gamma-Ray Flashes and Gamma-Ray Bursts observation

Fast Gamma ray Spectrometer (FGS) is an on-going detector development for the observation of transient gamma ray events such as Terrestrial Gamma ray Flashes (TGFs) produced in Earth’s thunderstorms and Gamma Ray Bursts (GRBs) produced in the far Universe. In this work, we compare different Cerium-doped Gadolinium Aluminium Gallium Garnet (GAGG:Ce) scintillators, associated with Silicon Photo-Multipliers (SiPMs), quantifying their performances at atmospheric pressure and under vacuum, with different surface conditions. We also study their afterglow following proton irradiation, similar to what will be observed in space environment. Our measurements with GAGG:Ce scintillators after proton irradiation confirm that GAGG:Ce can be used in space.

AM3: An Open-source Tool for Time-dependent Lepto-hadronic Modeling of Astrophysical Sources

We present the Astrophysical Multimessenger Modeling (AM 3 ) software. AM 3 is a documented open-source software (source code at https://gitlab.desy.de/am3/am3; user guide and documentation at https://am3.readthedocs.io/en/latest/) that efficiently solves the coupled integro-differential equations describing the temporal evolution of the spectral densities of particles interacting in astrophysical environments, including photons, electrons, positrons, protons, neutrons, pions, muons, and neutrinos. The software has been extensively used to simulate the multiwavelength and neutrino emission from active galactic nuclei (including blazars), gamma-ray bursts, and tidal disruption events. The simulations include all relevant nonthermal processes, namely synchrotron emission, inverse Compton scattering, photon–photon annihilation, proton–proton and proton–photon pion production, and photo-pair production. The software self-consistently calculates the full cascade of primary and secondary particles, including nonlinear feedback processes and predictions in the time domain. It also allows the user to track separately the particle densities produced by means of each distinct interaction process, including the different hadronic channels. With its efficient hybrid solver combining analytical and numerical techniques, AM 3 combines efficiency and accuracy at a user-adjustable level. We describe the technical details of the numerical framework and present three examples of applications to different astrophysical environments.

Off-Axis Color Characteristics of Binary Neutron Star Merger Events: Applications for Space Multi-Band Variable Object Monitor and James Webb Space Telescope

With advancements in gravitational wave detection technology, an increasing number of binary neutron star (BNS) merger events are expected to be detected. Due to the narrow opening angle of jet cores, many BNS merger events occur off-axis, resulting in numerous gamma-ray bursts (GRBs) going undetected. Models suggest that kilonovae, which can be observed off-axis, offer more opportunities to be detected in the optical/near-infrared band as electromagnetic counterparts of BNS merger events. In this study, we calculate kilonova emission using a three-dimensional semi-analytical code and model the GRB afterglow emission with the open-source Python package afterglowpy at various inclination angles. Our results show that it is possible to identify the kilonova signal from the observed color evolution of BNS merger events. We also deduce the optimal observing window for SVOM/VT and JWST/NIRCam, which depends on the viewing angle, jet opening angle, and circumburst density. These parameters can be cross-checked with the multi-band afterglow fitting. We suggest that kilonovae are more likely to be identified at larger inclination angles, which can also help determine whether the observed signals without accompanying GRBs originate from BNS mergers.

Generalized linear model study of the T90–T50 relation of gamma-ray bursts

ABSTRACT 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.

Towards a new model-independent calibration of Gamma-Ray Bursts

Current data on baryon acoustic oscillations and Supernovae of Type Ia (SNIa) cover up to z∼2.5. These low-redshift observations play a very important role in the determination of cosmological parameters and have been widely used to constrain the ΛCDM and models beyond the standard, such as the ones with open curvature. To extend this investigation to higher redshifts, Gamma-Ray Bursts (GRBs) stand out as one of the most promising observables. In spite of being transient, they are extremely energetic and can be used to probe the universe up to z∼9.4. They exhibit characteristics that suggest they are potentially standardizable candles and this allows their use to extend the distance ladder beyond SNIa. The use of GRB correlations is still a challenge due to the spread in their intrinsic properties. One of the correlations that can be employed for the standardization is the fundamental plane relation between the peak prompt luminosity, the rest-frame end time of the plateau phase, and its corresponding luminosity, also known as the three-dimensional Dainotti correlation. In this work, we propose an innovative method of calibration of the Dainotti relation which is independent of cosmology. We employ state-of-the-art data on Cosmic Chronometers (CCH) at z≲2 and use the Gaussian Processes Bayesian reconstruction tool. To match the CCH redshift range, we select 20 long GRBs in the range 0.553≤z≤1.96 from the Platinum sample, which consists of well-defined GRB plateau properties that obey the fundamental plane relation. To ensure the generality of our method, we verify that the choice of priors on the parameters of the Dainotti relation and the modeling of CCH uncertainties and covariance have negligible impact on our results. Moreover, we consider the case in which the redshift evolution of the physical features of the plane is accounted for. We find that the use of CCH allows us to identify a sub-sample of GRBs that adhere even more closely to the fundamental plane relation, with an intrinsic scatter of σint=0.20−0.05+0.03 obtained in this analysis when evolutionary effects are considered. In an epoch in which we strive to reduce uncertainties on the variables of the GRB correlations in order to tighten constraints on cosmological parameters, we have found a novel model-independent approach to pinpoint a sub-sample that can thus represent a valuable set of standardizable candles. This allows us to extend the cosmic distance ladder presenting a new catalog of calibrated luminosity distances up to z=5.

Direct Evidence for Preburst Stage of Gamma-Ray Burst from GRB 221009A Data

Previous research on Lorentz invariance violation in photons from gamma-ray bursts (GRBs) suggested a scenario where multi-GeV photons could be emitted before lower-energy photons at the GRB source frame. This implies the existence of a new preburst phase in addition to the traditionally identified prompt and afterglow stages observed in earlier studies. In this study, we present direct evidence for this novel preburst phase in GRBs based on recent observations of GRB 221009A. Our analysis leverages data from the Fermi Gamma-ray Burst Monitor and Large Area Telescope detectors of the Fermi Gamma-ray Space Telescope, as well as data from the KM2A detector of the Large High Altitude Air-shower Observatory.

Modelling of long gamma-ray burst host galaxies at cosmic noon from damped Lyman-α absorption statistics

ABSTRACT 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.

Gamma-ray flashes offer clues about thunderstorm electrification

Gamma-ray flashes offer clues about thunderstorm electrification

A simulation study on the sub-threshold joint gravitational wave-electromagnetic wave observation on binary neutron star mergers

Abstract 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 Pjoint, which is in analogue to Pastro in GW only observations. By simulating BNS merger GWs jointly detected by the HLV network and EM counterparts (kilonovae and short Gamma-ray bursts, sGRBs) with an assumed merger rate density of BNS, we generate catalogs of GW events and EM counterparts. Through this simulation, we analyze joint detection pairs, both correct and misidentified. We find the following: 1. For kilonovae, requiring Pjoint &amp;gt; 95% instead of $P_{\rm astro}&amp;gt;95~{{\%}}$ 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%; 2. For sGRBs, requiring Pjoint &amp;gt; 95% instead of Pastro reduces the S/N from 9.2 to 8.1-8.5; 3. Increasing kilonova or sGRB detection capability does not improve Pjoint 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% of its original value, and sub-threshold GW and sGRB observations can enhance the precision of constraining the speed of GWs to 88% of previously established values.

Synchrotron self-Compton in a radiative-adiabatic fireball scenario: Modelling the multiwavelength observations in some Fermi/LAT bursts

Abstract Energetic GeV photons expected from the closest and the most energetic Gamma-ray bursts (GRBs) provide an unique opportunity to study the very-high-energy emission as well as the possible correlations with lower energy bands in realistic GRB afterglow models. In the standard GRB afterglow model, the relativistic homogeneous shock is usually considered to be fully adiabatic, however, it could be partially radiative. Based on the external forward-shock scenario in both stellar wind and constant-density medium. We present a radiative-adiabatic analytical model of the synchrotron self-Compton (SSC) and synchrotron processes considering an electron energy distribution with a power-law index of 1 &amp;lt; p &amp;lt; 2 and 2 ≤ p. We show that the SSC scenario plays a relevant role in the radiative parameter ε, leading to a prolonged evolution during the slow cooling regime. In a particular case, we derive the Fermi/LAT light curves together with the photons with energies ≥100 MeV in a sample of nine bursts from the second Fermi/LAT GRB catalog that exhibited temporal and spectral indices with ≳ 1.5 and ≈2, respectively. These events can hardly be described with closure relations of the standard synchrotron afterglow model, and also exhibit energetic photons above the synchrotron limit. We have modeled the multi-wavelength observations of our sample to constrain the microphysical parameters, the circumburst density, the bulk Lorentz factor and the mechanism responsible for explaining the energetic GeV photons.

Polarization from a Radially Stratified GRB Outflow

While the dominant radiation mechanism of gamma-ray bursts (GRBs) remains a question of debate, synchrotron emission is one of the foremost candidates to describe the multi-wavelength afterglow observations. As such, it is expected that GRBs should present some degree of polarization across their evolution—presenting a feasible means of probing these bursts’ energetic and angular properties. Although obtaining polarization data is difficult due to the inherent complexities regarding GRB observations, advances are being made, and theoretical modeling of synchrotron polarization is now more relevant than ever. In this manuscript, we present the polarization for a fiduciary model, where the synchrotron FS emission evolving in the radiative–adiabatic regime is described by a radially stratified off-axis outflow. This is parameterized with a power-law velocity distribution and decelerated in a constant-density and wind-like external environment. We apply this theoretical polarization model for two select GRBs, presenting upper limits in their polarization—GRB 170817A, a known off-axis GRB with radio polarization upper limits, and GRB 190014C, an on-axis case, where the burst was seen from within the half-opening angle of the jet, with observed optical polarization—in an attempt to constrain their magnetic field geometry in the emitting region.

Diversity in Fermi/GBM Gamma-Ray Bursts: New Insights from Machine Learning

Classification of gamma-ray bursts (GRBs) has been a long-standing puzzle in high-energy astrophysics. Recent observations challenge the traditional short versus long viewpoint, where long GRBs are thought to originate from the collapse of massive stars and short GRBs from compact binary mergers. Machine learning (ML) algorithms have been instrumental in addressing this problem, revealing five distinct GRB groups within the Swift Burst Alert Telescope (BAT) light-curve data, two of which are associated with kilonovae (KNe). In this work, we extend our analysis to the Fermi Gamma-ray Burst Monitor catalog and identify five clusters using unsupervised ML techniques, consistent with the Swift/BAT results. These five clusters are well separated in the fluence-duration plane, hinting at a potential link between fluence, duration, and complexities (or structures) in the light curves of GRBs. Further, we confirm two distinct classes of KN-associated GRBs. The presence of GRB 170817A in one of the two KN-associated clusters lends evidence to the hypothesis that this class of GRBs could potentially be produced by binary neutron star mergers. The second KN-associated GRB cluster could potentially originate from neutron star–black hole mergers. Future multimessenger observations of compact binaries in gravitational waves and electromagnetic waves can be paramount in understanding these clusters better.

Varying linear polarisation in the dust-free gamma-ray burst 210610B

Context. Long gamma-ray bursts (GRBs) are produced by the collapse of some very massive stars, that emit ultra-relativistic jets. When the jets collide with the interstellar medium they decelerate and generate the so-called afterglow emission, which has been observed to be polarised. Aims. We study the polarimetric evolution of the GRB 210610B afterglow, at z = 1.1341. This allows us to evaluate the role of geometric and/or magnetic mechanisms in the GRB afterglow polarisation. Methods. We observed GRB 210610B using imaging polarimetry with CAFOS on the 2.2 m Calar Alto Telescope and FORS2 on the 4 × 8.1 m Very Large Telescope. Complementary optical spectroscopy was obtained with OSIRIS on the 10.4 m Gran Telescopio Canarias. We studied the GRB light-curve from X-rays to the optical bands and the Spectral Energy Distribution (SED). This allowed us to strongly constrain the line-of-sight extinction. Finally, we studied the GRB host galaxy using optical to NIR data to fit the SED and derive its integrated properties. Results. GRB 210610B had a bright afterglow with a negligible line-of-sight extinction. Polarimetry was obtained at three epochs: during an early plateau phase, at the time when the light curve breaks, and after the light curve steepened. We observe an initial polarisation of ∼4% that goes to zero at the time of the break, and it then again increases to ∼2%, with a change in the position angle of 54 ± 9 deg. The spectrum shows features with very low equivalent widths. This indicate a small amount of material in the line of sight within the host. Conclusions. The lack of dust and the low amount of material in the line of sight to GRB 210610B allowed us to study the intrinsic polarisation of the GRB optical afterglow. The GRB polarisation signals are consistent with ordered magnetic fields in refreshed shock or/and hydrodynamics-scale turbulent fields in the forward shock.