Origin Of Gamma-ray Bursts Research Articles

Identifying the Physical Origin of Gamma-Ray Bursts with Supervised Machine Learning

The empirical classification of gamma-ray bursts (GRBs) into long and short GRBs based on their durations is already firmly established. This empirical classification is generally linked to the physical classification of GRBs originating from compact binary mergers and GRBs originating from massive star collapses, or Type I and II GRBs, with the majority of short GRBs belonging to Type I and the majority of long GRBs belonging to Type II. However, there is a significant overlap in the duration distributions of long and short GRBs. Furthermore, some intermingled GRBs, i.e., short-duration Type II and long-duration Type I GRBs, have been reported. A multiparameter classification scheme of GRBs is evidently needed. In this paper, we seek to build such a classification scheme with supervised machine-learning methods, chiefly XGBoost. We utilize the GRB Big Table and Greiner’s GRB catalog and divide the input features into three subgroups: prompt emission, afterglow, and host galaxy. We find that the prompt emission subgroup performs the best in distinguishing between Type I and II GRBs. We also find the most important distinguishing features in prompt emission to be T 90, the hardness ratio, and fluence. After building the machine-learning model, we apply it to the currently unclassified GRBs to predict their probabilities of being either GRB class, and we assign the most probable class of each GRB to be its possible physical class.

Machine-learning points to possible origins of gamma-ray bursts

Machine-learning points to possible origins of gamma-ray bursts

New evidence of multiple channels for the origin of gamma-ray bursts with extended emission

ABSTRACT Gamma-ray bursts (GRBs) are the most intense explosions in the Universe. GRBs with extended emission (GRBs EE) constitute a small subclass of GRBs. GRBs EE are divided into EE-I GRBs and EE-II GRBs, according to the Amati empirical relationship rather than duration. We test here if these two types of GRB have different origins based on their luminosity function (and formation rate). Therefore, we use Lynden-Bell’s c− method to investigate the luminosity function and formation rate of GRBs with EE without any assumption. We calculate the formation rate of two types of GRBs. For EE-I GRBs, the fitting function can be written as ρ(z) ∝ (1 + z)−0.34 ± 0.04 for z < 2.39 and ρ(z) ∝ (1 + z)−2.34 ± 0.24 for z > 2.39. The formation rate of EE-II can describe as ρ(z) ∝ (1 + z)−1.05 ± 1.10 for z < 0.43 and ρ(z) ∝ (1 + z)−8.44 ± 1.10 for z > 0.43. The local formation rate is $\rho (0) = 0.03\, {\rm Gpc}^{-3} \, {\rm yr}^{-1}$ for some EE-I GRBs and $\rho (0) = 0.32 \, {\rm Gpc}^{-3} \, {\rm yr}^{-1}$ for EE-II GRBs. Based on these results, we provide new evidence that the origins of EE-I GRBs are different from EE-II GRBs from the perspective of event rate. The EE-I GRB could be produced from the death of the massive star, but EE-II GRB may come from other processes that are unrelated to the star formation rate. Our findings indicate that the GRBs with EE could have multiple production channels.

Constraints on Gamma-Ray Burst Models from GRB 221009A: GeV Gamma Rays versus High-energy Neutrinos

Gamma-ray bursts (GRBs) are generally believed to be efficient particle accelerators. In the presence of energetic protons in a GRB jet, interactions between these protons and the intense radiation field of the GRB are supposed to induce an electromagnetic cascade. Electrons/positrons generated in the cascade will produce an additional spectrum of a robust feature, which is in the form of a power-law distribution up to a GeV regime with an index of ≲2. We suggest that measurements of the Fermi Large Area Telescope at the GeV band can provide independent constraints on the key GRB model parameters such as the dissipation radius, the jet’s bulk Lorentz factor, and the baryon loading factor. Taking GRB 221009A, the brightest GRB ever detected, as an example, we show that the constraints from GeV gamma-ray emission may be more stringent than that from the neutrino observation, providing us with deep insight into the origin of GRBs.

Detection of GeV Emission from an Ultralong Gamma-Ray Burst with the Fermi Large Area Telescope

GRB 220627A, detected by Fermi Gamma-ray Burst Monitor (GBM), shows two episodes of gamma-ray emission, which are separated by a ∼700 s long quiescent phase. Due to similar temporal shapes and spectra in the two episodes, GRB 220627A is speculated to be a gravitationally lensed gamma-ray burst (GRB). We analyze Fermi Large Area Telescope (LAT) data and find that about 49 gamma-ray photons above 100 MeV come from the GRB during the first episode, while there are no photons above 100 MeV in the second episode. Based on the broadband spectral study of the two episodes, the gravitationally lensing scenario can be ruled out at a high confidence level and we thus conclude that GRB 220627A is an intrinsically ultralong GRB with the prompt burst emission lasting longer than 1000 s. It is then the first case that GeV emission is detected from an ultralong GRB. We find that a short spike seen in the LAT light curve is also present in GBM detectors that see the burst, suggesting a common internal region of emission across the entire Fermi energy range. The detection of a 15.7 GeV photon during the early prompt phase places a lower limit of Γ ≥ 300 on the bulk Lorentz factor of the GRB ejecta. The constraint on the bulk Lorentz factor could shed light on the origin of ultralong GRBs.

ALMA Host Galaxy Observation of the Off-axis Gamma-Ray Burst XRF 020903

Abstract We investigated the radio properties of the host galaxy of X-ray flash, XRF 020903, which is the best example for investigating the off-axis origin of gamma-ray bursts (GRBs). Dust continuum at 233 GHz and CO are observed using the Atacama Large millimeter/submillimeter array. The molecular gas mass derived by applying the metallicity-dependent CO-to-H2 conversion factor matches the global trend along the redshift and stellar mass of the GRB host galaxies. The estimated gas depletion timescale (pertaining to the potential critical characteristics of GRB host galaxies) is equivalent to those of GRBs and super-luminous supernova hosts in the same redshift range. These properties of the XRF 020903 host galaxy observed in radio resemble those of GRB host galaxies, thereby supporting the identical origin of XRF 020903 and GRBs.

The Novel and Common Origin of Gamma-ray Bursts: A Galactic Seed Separation with Emitting Radiations

The mechanism of the gamma-ray burst is uncertain while the current candidates, respectively, for short and long GRBs are rather accepted. They conflict with some observed facts. Here we examine in detail the process for an energy circulation to separate to two ones by the energy circulation theory. We derive the equations of the force and the potential energy for the separation of a galactic seed. A galactic seed divides to two seeds orthogonally. If the receding speed is high enough, two seeds separate away orthogonally. If not enough, they are trapped at the energy trough, from where a subsequent flat separation occurs. The difference in the potential energy is partly emitted as gamma-ray radiations. The proposed process nicely meets the observed features of the GRBs, which the standard cosmology cannot explain. The GRBs are an important evidence to support our proposed model of galactic evolution, which includes galactic seed separations, as well as its basis; the energy circulation theory. Another key evidence, which we reported previously, is that the model predicts a constant speed of a galaxy rotation at any radial distances without dark matter.

One star, two stars, or both? Investigating metallicity-dependent models for gamma-ray burst progenitors with the IllustrisTNG simulation

ABSTRACT The rate of long-duration gamma-ray bursts (GRBs) has been identified as a potential proxy for the star formation rate (SFR) across redshift, but the exact relationship depends on GRB progenitor models (single versus binary). The single-progenitor collapsar model accounts for the preference towards low-metallicity GRB progenitors, but is in apparent tension with some high-metallicity GRB host galaxy measurements. As a possible solution, we consider the scenario where high-metallicity GRB hosts harbour low-metallicity regions in which GRB progenitors form. For this, we use the IllustrisTNG cosmological hydrodynamical simulation to investigate the internal metallicity distribution of GRB hosts, implementing in post-processing different GRB formation models. Predictions (GRB rate, host metallicities, and stellar masses) are compared to the high-completeness GRB legacy surveys BAT6 and SHOALS and a sample of high-redshift GRB-DLA metallicities, allowing us to compute their relative likelihoods. When the internal metallicity distribution of galaxies is ignored, the best-fitting model requires a metallicity-independent channel, as previously proposed by Trenti, Perna, & Jimenez. However, when the internal metallicity distribution is considered, a basic metallicity bias model with a cutoff at $Z_{\rm max}=0.35\, \mathrm{\it Z}_\odot$ is the best-fitting one. Current data are insufficient to discriminate among more realistic metallicity bias models, such as weak metallicity dependence of massive binaries versus stronger metallicity bias of collapsars. An increased sample of objects, and direct measurements of host stellar masses at redshift z > 2 would allow to further constrain the origin of long GRBs.

Fermi-GBM Follow-up of LIGO-Virgo Binary Black Hole Mergers: Detection Prospects

Abstract Fermi-Gamma-ray Burst Monitor observed a 1 s long gamma-ray signal (GW150914-GBM) starting 0.4 s after the first gravitational-wave detection from the binary black hole (BH) merger GW150914. GW150914-GBM is consistent with a short gamma-ray burst origin; however, no unambiguous claims can be made as to the physical association of the two signals due to a combination of low gamma-ray flux and the unfavorable location of Fermi-GBM. Here we answer the following question: if GW150914 and GW150914-GBM were associated, how many LIGO-Virgo binary BH mergers would Fermi-GBM have to follow up to detect a second source? To answer this question, we perform simulated observations of binary BH mergers with LIGO-Virgo and adopt different scenarios for gamma-ray emission from the literature. We calculate the ratio of simulated binary BH mergers detected by LIGO-Virgo to the number of gamma-ray counterpart detections by Fermi-GBM, the BBH-to-GRB ratio. A large majority of the models considered here predict a BBH-to-GRB ratio in the range of 5–20, but for optimistic cases it can be as low as 2, while for pessimistic assumptions it can be as high as 700. Hence, we expect that the third observing run, with its high rate of binary BH detections and assuming the absence of a joint detection, will provide strong constraints on the presented models.

The case for a high-redshift origin of GRB 100205A

Abstract The number of long gamma-ray bursts (GRBs) known to have occurred in the distant Universe (z > 5) is small (∼15); however, these events provide a powerful way of probing star formation at the onset of galaxy evolution. In this paper, we present the case for GRB 100205A being a largely overlooked high-redshift event. While initially noted as a high-z candidate, this event and its host galaxy have not been explored in detail. By combining optical and near-infrared Gemini afterglow imaging (at t < 1.3 d since burst) with deep late-time limits on host emission from the Hubble Space Telescope, we show that the most likely scenario is that GRB 100205A arose in the range 4 < z < 8. GRB 100205A is an example of a burst whose afterglow, even at ∼1 h post burst, could only be identified by 8-m class IR observations, and suggests that such observations of all optically dark bursts may be necessary to significantly enhance the number of high-redshift GRBs known.

Inverse Compton Scattering Spectra of Gamma-Ray Burst Prompt Emission

Abstract Although the physical origin of gamma-ray burst (GRB) prompt emission is still controversial, synchrotron radiation from accelerated electrons is a promising mechanism. It is believed that electrons are accelerated continuously by ultra-relativistic shocks or magnetic reconnections. At the same time, these electrons will be cooled via several processes (mainly adiabatic expansion, synchrotron radiation, and inverse Compton scattering (ICS)), which regulate the distribution of electrons. An extra high-energy spectrum component is expected to be induced by ICS. However, the gamma–gamma annihilation effect may eliminate the high-energy photons and prevent the observers from distinguishing the extra component. We perform numerical calculations by taking these effects into account and discuss whether the extra ICS component could be observed. By exploring the plausible parameter space for relevant quantities of the GRB ejecta, we present the electron distributions and the corresponding spectra of synchrotron radiation and ICS. It is found that the extra component is observable only for ejecta with a rather large bulk Lorentz factor. A large Lorentz factor means the adiabatic expansion is the leading process in the electron cooling procedure, which makes the low-energy electron distribution spectrum relatively hard. Therefore, the ICS component is more likely to be detected for GRBs that have a hard low-energy photon spectrum.

The key role of BeppoSAX in the GRB history

Twenty years have already been elapsed from the BeppoSAX discovery of the first afterglow of a Gamma-Ray Burst (GRB) in February 28, 1997. Thanks to this discovery, it was possible to unveil the 30 year mystery about GRB origin: GRBs are huge explosions in galaxies at cosmological distances. Starting from the first GRB detection with Vela satellites, I will review the main results obtained before BeppoSAX, the story of the BeppoSAX discovery of the GRB afterglow with the consequent cosmological distance determination, the main BeppoSAX results, and those obtained after the BeppoSAX era until nowadays with the still open problems and prospects.

On the Magnetar Origin of the GRBs Presenting X-Ray Afterglow Plateaus

Abstract The X-ray afterglow plateau emission observed in many gamma-ray bursts (GRBs) has been interpreted as being fueled either by fallback onto a newly formed black hole or by the spin-down luminosity of an ultra-magnetized millisecond neutron star. If the latter model is assumed, GRB X-ray afterglow light curves can be reproduced analytically. We fit a sample of GRB X-ray plateaus, interestingly yielding a distribution in the diagram of magnetic field versus spin period (B–P) consistent with B ∝ P 7/6, which is consistent with GRB expectations of the well-established physics of the spin-up line for accreting Galactic X-ray pulsars. The normalization of the relation that we obtain perfectly matches spin-up line predictions for typical neutron star masses (∼1 M ⊙) and radii (∼10 km), and for mass accretion rates typically expected in GRBs, . Short GRBs with extended emission (SEEs) appear toward the long-period end of the distribution, and long GRBs (LGRBs) toward the short-period end. This result is consistent with expectations from the spin-up limit, where the total accreted mass determines the position of the neutron star in the B–P diagram. The B–P distributions for LGRBs and SEEs are statistically different, further supporting the idea that the fundamental plane relation—a tri-dimensional correlation between the X-ray luminosity at the end of the plateau, the end time of the plateau, and the 1 s peak luminosity in the prompt emission—is a powerful discriminant among those populations. Our conclusions are robust against suppositions regarding the collimation angle of the GRB and the magnetar braking index, which shift the resulting properties of the magnetar parallel to the spin-up line, and strongly support a magnetar origin for GRBs presenting X-ray plateaus.

Low-luminosity gamma-ray bursts as the sources of ultrahigh-energy cosmic ray nuclei

Recent results from the Pierre Auger Collaboration have shown that the composition of ultrahigh-energy cosmic rays (UHECRs) becomes gradually heavier with increasing energy. Although gamma-ray bursts (GRBs) have been promising sources of UHECRs, it is still unclear whether they can account for the Auger results because of their unknown nuclear composition of ejected UHECRs. In this work, we revisit the possibility that low-luminosity GRBs (LL GRBs) act as the sources of UHECR nuclei, and give new predictions based on the intrajet nuclear composition models considering progenitor dependencies. We find that the nuclear component in the jet can be divided into two groups according to the mass fraction of silicon nuclei, Si-free and Si-rich. Motivated by the connection between LL GRBs and transrelativistic supernovae, we also consider the hypernova ejecta composition. Then, we discuss the survivability of UHECR nuclei in the jet base and internal shocks of the jets, and show that it is easier for nuclei to survive for typical LL GRBs. Finally, we numerically propagate UHECR nuclei ejected from LL GRBs with different composition models and compare the resulting spectra and composition to Auger data. Our results show that both the Si-rich progenitor and hypernova ejecta models match the Auger data well, while the Si-free progenitor models have more difficulty in fitting the spectrum. We argue that our model is consistent with the newly reported cross correlation between the UHECRs and starburst galaxies, since both LL GRBs and hypernovae are expected to be tracers of the star-formation activity. LL GRBs have also been suggested as the dominant origin of IceCube neutrinos in the PeV range, and the LL GRB origin of UHECRs can be critically tested by near-future multimessenger observations.

Possible correlations between gamma-ray burst and its host galaxy offset

We collected the information of 304 gamma-ray bursts (GRBs) from the literature, and analyzed the correlations among the host galaxy offsets (the distance from the site of the GRB to the center of its host galaxy), T90,i (the duration T90 in rest-frame), TR45,i (the duration TR45 in rest-frame), Eγ,iso (the isotropic equivalent energy), Lγ,iso (=Eγ,iso/T90,i, the isotropic equivalent luminosity) and Lpk (peak luminosity). We found that T90,i, TR45,i, Eγ,iso, Lpk have negative correlation with offset, which is consistent with origin of short GRBs (SGRBs) and long GRBs (LGRBs). On separate analysis, we found similar results for log⁡Eγ,iso−log⁡(offset) and log⁡Lpk−log⁡(offset) relations in case of SGRBs only, while no obvious relation for LGRBs. There is no correlations between offset and Lγ,iso. We also put the special GRB 170817A and GRB 060218A on the plots. The two GRBs both have low luminosity and small offset. In the log⁡(offset)−log⁡T90,i plot, we found GRB 170817A locates in between the two regions of SGRBs and LGRBs and it is the outlier in the offset−Eγ,iso, offset−Lγ,iso and offset−Lpk plots. Together with GRB 060218A being an outlier in all plots, it indicates the speciality of GRBs 170817A and 060218A, and might imply more subgroups of the GRB samples.

On The Origin of Supernova-less Long Gamma-Ray Bursts

Abstract The fraction of long duration gamma-ray bursts (GRBs) without an associated bright supernova (SN-less GRBs) at low redshifts is comparable to that of GRBs associated with bright supernovae (SN-GRBs). The prompt emission and its fast decline phase in both types of GRBs are well described by the cannonball model of GRBs, where inverse Compton scattering of ambient light is the dominant γ-ray production mechanism. However, in SN-less GRBs, the fast decay of the prompt emission appears to be overtaken by an afterglow powered by a millisecond pulsar, while, in SN-GRBs, the late-time X-ray afterglow is well described by synchrotron radiation from the decelerating jet in the interstellar medium. We use their different X-ray light curves to determine the ratio of SN-less GRBs/SN-GRBs at very high redshifts. We find that at z > 4, this ratio is the same as that at small redshifts. Such a z-independent ratio suggests that the origin of SN-less GRBs is a phase transition of neutron stars to quark stars in high-mass X-ray binaries, rather than the merger of neutron stars.

Gravitational Waves and Gamma-Rays from a Binary Neutron Star Merger: GW170817 and GRB 170817A

Abstract On 2017 August 17, the gravitational-wave event GW170817 was observed by the Advanced LIGO and Virgo detectors, and the gamma-ray burst (GRB) GRB 170817A was observed independently by the Fermi Gamma-ray Burst Monitor, and the Anti-Coincidence Shield for the Spectrometer for the International Gamma-Ray Astrophysics Laboratory. The probability of the near-simultaneous temporal and spatial observation of GRB 170817A and GW170817 occurring by chance is 5.0 × 10 − 8 . We therefore confirm binary neutron star mergers as a progenitor of short GRBs. The association of GW170817 and GRB 170817A provides new insight into fundamental physics and the origin of short GRBs. We use the observed time delay of ( + 1.74 ± 0.05 ) s between GRB 170817A and GW170817 to: (i) constrain the difference between the speed of gravity and the speed of light to be between − 3 × 10 − 15 and + 7 × 10 − 16 times the speed of light, (ii) place new bounds on the violation of Lorentz invariance, (iii) present a new test of the equivalence principle by constraining the Shapiro delay between gravitational and electromagnetic radiation. We also use the time delay to constrain the size and bulk Lorentz factor of the region emitting the gamma-rays. GRB 170817A is the closest short GRB with a known distance, but is between 2 and 6 orders of magnitude less energetic than other bursts with measured redshift. A new generation of gamma-ray detectors, and subthreshold searches in existing detectors, will be essential to detect similar short bursts at greater distances. Finally, we predict a joint detection rate for the Fermi Gamma-ray Burst Monitor and the Advanced LIGO and Virgo detectors of 0.1–1.4 per year during the 2018–2019 observing run and 0.3–1.7 per year at design sensitivity.

Optical and X-ray early follow-up of ANTARES neutrino alerts

High-energy neutrinos could be produced in the interaction of charged cosmic rays with matter or radiation surrounding astrophysical sources. Even with the recent detection of extraterrestrial high-energy neutrinos by the IceCube experiment, no astrophysical neutrino source has yet been discovered. Transient sources, such as gamma-ray bursts, core-collapse supernovae, or active galactic nuclei are promising candidates. Multi-messenger programs offer a unique opportunity to detect these transient sources. By combining the information provided by the ANTARES neutrino telescope with information coming from other observatories, the probability of detecting a source is enhanced, allowing the possibility of identifying a neutrino progenitor from a single detected event.A method based on optical and X-ray follow-ups of high-energy neutrino alerts has been developed within the ANTARES collaboration. This method does not require any assumptions on the relation between neutrino and photon spectra other than time-correlation. This program, denoted as TAToO, triggers a network of robotic optical telescopes (TAROT and ROTSE) and the Swift-XRT with a delay of only a few seconds after a neutrino detection, and is therefore well-suited to search for fast transient sources. To identify an optical or X-ray counterpart to a neutrino signal, the images provided by the follow-up observations are analysed with dedicated pipelines. A total of 42 alerts with optical and 7 alerts with X-ray images taken with a maximum delay of 24 hours after the neutrino trigger have been analysed. No optical or X-ray counterparts associated to the neutrino triggers have been found, and upper limits on transient source magnitudes have been derived. The probability to reject the gamma-ray burst origin hypothesis has been computed for each alert.

Search for low-energy neutrinos from gamma-ray bursts at the Baksan Underground Scintillation Telescope

The origin of gamma-ray bursts is still one of the unresolved problems in physics. They are short, intense, and non-repeating flashes of MeV gamma-rays with a wide range of spectral and temporal properties. Also these bursts are perhaps sources of neutrino emission. Unlike the photons, which may scatter or be absorbed, the neutrinos, due to their small interaction cross section, arrive at the Earth unaffected. This paper describes experimental methods for detection of low energy neutrinos in the range from 20 MeV to 100MeV at the Baksan Underground Scintillation Telescope. In the analysis we search neutrinos in time coincidence with a gamma-ray burst. We use filtered data collected at the Telescope during 2012. We also use the catalogue of gamma-ray bursts of the SWIFT satellite experiment.

A SIZE-DURATION TREND FOR GAMMA-RAY BURST PROGENITORS

Gamma-ray bursts (GRBs) show a bimodal distribution of durations, separated at a duration of ~2 s. Observations have confirmed the association of long GRBs with the collapse of massive stars. The origin of short GRBs is still being explored. We examine constraints on the emission region size in short and long GRBs detected by Fermi/GBM. We find that the emission region size during the prompt emission, R, and the burst duration, T$_{90}$, are consistent with the relation R ~ c x T$_{90}$, for both long and short GRBs. We find the characteristic size for the prompt emission region to be ~2 x 10$^{10}$ cm, and ~4 x 10$^{11}$ cm for short and long GRBs, respectively.