Gamma-ray Bursts Candidates Research Articles

Monitoring of space radiation and electromagnetic transients by Moscow State University nano-satellites

Nano-satellites of cubesat format can be used effectively to study different aspects of space weather phenomena, such as high energy charge particle flux variations at near-Earth space as well as for monitoring cosmic gamma-ray bursts (GRBs) and hard X-ray and gamma-ray emission of solar flares. Using a constellation of CubeSats enables cost-effective synchronous measurements of radiation fluxes at different points in space, effectively separating the spatial and temporal effects of observed flux variations.Since July 5, 2019, M. V. Lomonosov Moscow State University (MSU) has realized its own program of cubesat employment. To the present date, 18 satellites in 1.5U, 3U, and 6U formats with the instruments developed at MSU have been launched, and 11 of them continue to operate on the solar-synchronous low-altitude orbits (400–600 km). The number of instruments elaborated especially for cubesats includes the universal Detector of Cosmic Radiation (DeCoR-1, DeCoR-2, and DeCoR-3 modifications), the Advanced Ultraviolet Radiometer (AURA, AURA-2) and the Complex Radiation Detector (CoRaD, i.e., KODIZ in Russian acronym). The DeCoR-1, DeCoR-2 and DeCoR-3 instruments allow for the detection of gamma-quanta and electrons in the energy ranges of 0.02–2.0 MeV and 0.3–10.0 MeV, respectively. The KODIZ instrument is intended especially to detect protons with energies higher than 300 MeV and electrons with energies higher than several MeV. The AURA and AURA-2 instruments are used to monitor atmospheric UV glow in ∼200–400 nm bands. Up until now, the good experience has been accumulated by using these instruments to measure different space weather effects, such as polar cups filling with solar cosmic rays, the dynamics of outer belt boundaries during geomagnetic storms, and electron precipitation in different areas of near-Earth space, including low-latitude regions. As a by-product, a number of GRB candidates were detected. The possibility of further development of multi-satellite group and perspectives to study the mentioned phenomena will be discussed in this paper.

Identification of Extended Emission Gamma-Ray Burst Candidates Using Machine Learning

Gamma-ray bursts (GRBs) have been classified traditionally based on their duration. The increasing number of extended emission (EE) GRBs, lasting typically more than 2s but with properties similar to those of short GRBs, challenges the traditional classification criteria. In this work, we use the t-distributed stochastic neighbor embedding (t-SNE), a machine-learning technique, to classify GRBs. We present the results for GRBs observed until 2022 July by the Swift/BAT (Burst Alert Telescope) instrument in all its energy bands. We show the effects of varying the learning rate and perplexity parameters as well as the benefit of preprocessing the data by a nonparametric noise-reduction technique. Consistently with previous works, we show that the t-SNE method separates GRBs into two subgroups. We also show that EE GRBs reported by various authors under different criteria tend to cluster in a few regions of our t-SNE maps and identify seven new EE GRB candidates by using the gamma-ray data provided by the automatic pipeline of Swift/BAT and the proximity with previously identified EE GRBs.

Lorentz Invariance Violation Test from Time Delays Measured with Gravitationally Lensed GRB Candidates 950830 and 200716C

The spectral lag features in gamma-ray bursts (GRBs) have been widely used to investigate possible Lorentz invariance violation (LIV). However, these constraints could depend on the unknown source-intrinsic time delays in different energy bands. Biesiada & Piórkowska theoretically proposed that gravitational lensing time delays in a strongly lensed GRB can become a tool for testing LIV free from the intrinsic time lag problem. Recently GRB 950830 and GRB 200716C have been proposed to be lensed by an intermediate-mass black hole. They should still be considered as candidates of strongly lensed bursts, since no angular offset (i.e., the evidence for multiple images) was detected, but only a double peak structure in the light curve. The redshift of the burst z s and of the lens z l have not been measured in either case; hence we assumed a reasonable guess of z l = 1.0, z s = 2.0 for GRB 950830 and z l = 0.174, z s = 0.348 for GRB 200716C. Bearing all this in mind, we attempted to constrain LIV theories in a prospective way based on the two GRBs by considering time delays between two pulses in different energy channels. By directly fitting the time delay data of GRBs 950830 and 200716C we obtained the following limits on LIV energy scale: E QG,1 ≥ 3.2 × 109 GeV and E QG,1 ≥ 6.3 × 109 GeV, respectively. Sensitivity analysis regarding the (unknown) redshifts leads to the most conservative estimate, E QG,1 ≥ 1.5 × 108 GeV for GRB 950830 and E QG,1 ≥ 4.8 × 108 GeV for GRB 200716C, when they would be located at z s ∼ 5.

A machine learning approach for GRB detection in AstroSat CZTI data

ABSTRACT We present a machine learning (ML) based method for automated detection of Gamma-Ray Burst (GRB) candidate events in the range 60–250 keV from the AstroSat Cadmium Zinc Telluride Imager data. We use density-based spatial clustering to detect excess power and carry out an unsupervised hierarchical clustering across all such events to identify the different light curves present in the data. This representation helps us to understand the instrument’s sensitivity to the various GRB populations and identify the major non-astrophysical noise artefacts present in the data. We use Dynamic Time Warping (DTW) to carry out template matching, which ensures the morphological similarity of the detected events with known typical GRB light curves. DTW alleviates the need for a dense template repository often required in matched filtering like searches. The use of a similarity metric facilitates outlier detection suitable for capturing previously unmodelled events. We briefly discuss the characteristics of 35 long GRB candidates detected using the pipeline and show that with minor modifications such as adaptive binning, the method is also sensitive to short GRB events. Augmenting the existing data analysis pipeline with such ML capabilities alleviates the need for extensive manual inspection, enabling quicker response to alerts received from other observatories such as the gravitational-wave detectors.

Search for Radio Remnants of Nearby Off-axis Gamma-Ray Bursts in a Sample of Swift/BAT Events

Abstract The multi-messenger discovery of gravitational waves (GWs) and light from the binary neutron star (NS) merger GW170817, associated with gamma-ray burst (GRB) 170817A and kilonova AT2017gfo, has marked the start of a new era in astrophysics. GW170817 has confirmed that binary NS mergers are progenitors of at least some short GRBs. The peculiar properties of the GRB 170817A radio afterglow, characterized by a delayed onset related to the off-axis geometry, have also demonstrated how some nearby short GRBs may not be identified as such with standard short-timescale electromagnetic follow-up observations. Building upon this new information, we performed late-time radio observations of a sample of four short GRBs with unknown redshift and no previously detected afterglow in the Swift/BAT sample in order to identify nearby ( Mpc) off-axis GRB candidates via their potential late-time radio signatures. We find a previously uncatalogued radio source within the error region of GRB 130626 with a flux density consistent with an NS radio flare at a distance of ∼100 Mpc. An origin related to a persistent radio source unrelated to the GRB cannot be excluded nor confirmed given the high chance of false positives in error regions as large as those considered here, and the limited time baseline of our observations. Further radio (and X-ray) follow-up observations are needed to better understand the origin of this source.

Potential Gravitational-wave and Gamma-ray Multi-messenger Candidate from 2015 October 30

Abstract We present a search for binary neutron star (BNS) mergers that produced gravitational waves during the first observing run of the Advanced Laser Interferometer Gravitational-Wave Observatory (LIGO), and gamma-ray emission seen by either the Swift-Burst Alert Telescope (BAT) or the Fermi-Gamma-ray Burst Monitor (GBM), similar to GW170817 and GRB 170817A. We introduce a new method using a combined ranking statistic to detect sources that do not produce significant gravitational-wave or gamma-ray burst candidates individually. The current version of this search can increase by 70% the detections of joint gravitational-wave and gamma-ray signals. We find one possible candidate observed by LIGO and Fermi-GBM, 1-OGC 151030, at a false alarm rate of 1 in 13 yr. If astrophysical, this candidate would correspond to a merger at Mpc with source-frame chirp mass of . If we assume that the viewing angle must be <30° to be observed by Fermi-GBM, our estimate of the distance would become Mpc. By comparing the rate of BNS mergers to our search-estimated rate of false alarms, we estimate that there is a 1 in 4 chance that this candidate is astrophysical in origin.

Lorentz violation from gamma-ray burst neutrinos

The Lorentz violation (LV) effect of ultra-relativistic particles can be tested by gamma-ray burst (GRB) neutrinos and photons. The IceCube Collaboration has observed plenty of ultra-high energy neutrinos, including four PeV scale neutrinos. Recent studies suggested a possible energy dependent speed variation of GRB neutrinos in a similar way to that of GRB photons. Here we find that all four PeV neutrinos with associated GRB candidates can satisfy a regularity found from TeV neutrinos about a linear form correlation between the observed time difference and the LV factor. Such regularity indicates a Lorentz violation scale ELV = (6.5 ± 0.4) × 1017 GeV, which is comparable with that determined by GRB photons. We also suggest that neutrinos and anti-neutrinos can be superluminal and subluminal respectively due to opposite signs of LV correction.

Catalog of short gamma-ray transients detected in the SPI/INTEGRAL experiment

We analyzed data obtained by the SPI telescope onboard the INTEGRAL observatory to search for short transient events with a duration from 1 ms to a few tens of seconds. An algorithm for identifying gamma-ray events against the background of a large number of charged particle interactions with the detector has been developed. The classification of events was made. Apart from the events associated with cosmic gamma-ray bursts (GRBs) confirmed by other space experiments and the activity of known soft gamma repeaters (for example, SGR 1806-20), previously unreported GRBs have been found. GRB candidates and short gamma-ray events probably associated with the activity of known SGRs and AXPs have been selected. The spectral evolution of 28 bright GRBs from the catalog has been studied extensively. A new method for investigating the spectral evolution is proposed. The energy dependence of the spectral lag for bursts with a simple structure of their light curves and for individual pulses of multipulse events is shown to be described by a logarithmic function, lag ~ A*log(E). It has been established that the parameter A depends on the pulse duration, with the dependence being universal for all of the investigated GRBs. No negative spectral lags have been detected for bursts with a simple structure of their light curves.

Imprint of Gravitational Lensing by Population III Stars in Gamma‐Ray Burst Light Curves

We propose a novel method of extracting the imprint of gravitational lensing by Population III stars in the light curves of gamma-ray bursts (GRBs). Significant portions of GRBs can originate in hypernovae of Population III stars and be gravitationally lensed by foreground Population III stars or their remnants. If the lens mass is on the order of 102-103 M☉ and the lens redshift is greater than 10, the time delay between two lensed images of a GRB is ≈1 s and the image separation is ≈10 μas. Although it is difficult to resolve the two lensed images spatially with current facilities, the light curves of the two images are superimposed with a delay of ≈1 s. GRB light curves usually exhibit noticeable variability, where each spike is less than 1 s. If a GRB is lensed, all spikes are superimposed with the same time delay. Hence, if the autocorrelation of the light curve with changing time interval is calculated, it should show resonance at the time delay of the lensed images. Applying this autocorrelation method to GRB light curves that are archived as the BATSE catalog, we demonstrate that more than half of the light curves show recognizable resonance they are lensed. Furthermore, in 1821 GRBs we actually find one candidate for a GRB lensed by a Population III star, which may be located at redshift 20-200. The present method is quite straightforward and therefore provides an effective tool for searching for Population III stars at redshift greater than 10. Using this method, we may find more candidates for GRBs lensed by Population III stars in the data of the Swift satellite.

Gamma-ray bursts associated with supernovae: a systematic analysis of BATSE GRB candidates

We examined the properties of a sample of BATSE Gamma--Ray Bursts (GRBs) comprising events which have indications of association with a supernova (SN), some on the basis of indications of re--brightening in the optical afterglow light curve, but in most cases based only on the `loose' temporal and directional coincidence inferred from the cross correlation of catalogs. Despite of the large uncertainties in the latter selection method, the temporal and spectral analysis reveal three interesting statistical results when the sample is compared with that of all the BATSE GRBs: the GRBs tentatively associated with SNe are found to predominantly (in $\sim$ 80% of the cases) have single-peaked light curves, a softer spectrum (i.e. low energy power law index $\alpha \sim$ --1.5) and tend not to follow the Lag-Luminosity and Isotropic Energy--Peak Energy correlations. These three independent statistical properties point toward the existence of a significant number of under-luminous,GRB 980425-like events constituting -- at least from an observational point of view -- a tail or a separate class with respect to the whole of the BATSE GRB events. The unusually high percentage of SN Ibc among those identified by the catalog cross--correlation (factor $\sim 4$ higher than expected from SN catalog statistics) reinforces the non-randomness of (some of) the selected events.

Analysis Methods and Results of a Search for Weak Gamma‐Ray Bursts in the BATSE Data

We report initial results on the statistical properties of the dimmest gamma-ray bursts (GRBs) observed with the Burst and Transient Source Experiment (BATSE), using new ground-based methods to obtain a sample of GRBs from 502 days of BATSE data. Using the most sensitive ground-based detection of GRBs, the sample extends to GRBs much fainter than those detected by the onboard trigger, but because of the temporal resolution of the data, the sample is limited to GRBs of duration of at least 2 s. For each detected event, Bayesian probabilities are calculated for the event to belong to each of seven classes of differing physical origins. The sample of GRB candidates is defined by the requirement that the Bayesian probability for belonging to the GRB class is higher than 0.5. The intensity distribution of the GRB sample is corrected using a Monte Carlo simulation of the postflight detection efficiency. The sky distribution of the dimmest BATSE bursts is consistent with isotropy. The dimmest bursts are softer than the brightest triggered bursts.

INTEGRAL Spectrometer SPI's GRB detection capabilities

The spectrometer SPI, one of the two main instruments of the INTEGRAL spacecraft, offers significant gamma-ray burst detection capabilities. In its 35° (full width) field of view SPI is able to localise gamma-ray bursts at a mean rate of ~0.8/month. With its large anticoincidence shield of 512 kg of BGO crystals SPI is able to detect gamma-ray bursts quasi omni-directionally with a very high sensitivity. Burst alerts of the anticoincidence shield are distributed by the INTEGRAL Burst Alert System. In the first 8 months of the mission about 0.8/day gamma-ray burst candidates and 0.3/day gamma-ray burst positions were obtained with the anticoincidence shield by interplanetary network triangulations with other spacecrafts.

Search for sub-TeV gamma rays in coincidence with gamma ray bursts

We report on a study of sub-TeV $(10\mathrm{GeV}<{E}_{\ensuremath{\gamma}}<1\mathrm{TeV})$ gamma-ray-induced muon secondaries in coincidence with BATSE gamma ray bursts (GRBs). Each TeV gamma ray striking the atmosphere produces $\ensuremath{\approx}0.2$ muons whose identity and angle can be measured by the Project GRAND array. Eight GRB candidates were studied; seven were selected based upon the optimum product of (detected BATSE fluence) $\ifmmode\times\else\texttimes\fi{}$ (GRAND's acceptance). One candidate was added because it was reported as a possible detection by the Milagrito Collaboration. Seven candidates show a positive, though not statistically significant, muon excess. The only significant possible coincidence shows an excess of $466\ifmmode\pm\else\textpm\fi{}171$ muons during the BATSE T90 time interval for GRB 971110. The chance probability of such an excess in GRAND's background at the time of this event is $3\ifmmode\times\else\texttimes\fi{}{10}^{\ensuremath{-}3}.$ The chance probability of observing such an excess in one of the eight bursts studied here is 0.025. If this event is real, the implied fluence of energetic $(>10\mathrm{GeV})$ gamma rays necessary to account for the observed muon excess would require that most of the GRB fluence arrived in the form of energetic gamma rays.

An Off‐Line Scan of the BATSE Daily Records and a Large Uniform Sample of Gamma‐Ray Bursts

During a scan of the archival BATSE daily records covering the entire 9.1 yr (TJD 8369-11690) of the BATSE operation, 3906 gamma-ray bursts (GRBs) have been detected. 2068 of these GRBs are previously known BATSE triggers, while 1838 of them are new nontriggered bursts. It is important that all events were detected in the same type of data and were processed with the same procedure. Therefore these 3906 GRBs constitute a uniform sample. We have created a publicly available electronic data base containing this sample. We describe the procedures of the data reduction, the selection of the GRB candidates, and the statistical tests for possible non-GRB contaminations. We also describe a novel test burst method used to measure the scan efficiency and the information obtained using the test bursts. Our scan decreases the BATSE detection threshold to ~0.1 photon s-1 cm-2. As a first result, we show that the differential log N- log P distribution corrected for the detection efficiency extends to low brightnesses without any indication of a turnover. Any reasonable extrapolation of the new log N- log P to lower brightnesses imply a rate of several thousands of GRBs in the universe per year.

Features of Neutrino Signals from Collapsars

In this study, we investigate the luminosity and energy spectrum of neutrinos from a collapsar, which is one of the most probable candidates for Gamma-Ray Bursts. We also estimate the event number from a burst, as well as the detection rate. We show that the total energy of neutrinos depends strongly on many environmental physical parameters, such as the total accreting mass and the mass accretion rate. This is in striking contrast to the case of Supernova. We estimate that the total event number R measured by TITAND will be R ∼ 1 when the source is located 30 Mpc away from the earth. The detection rate could be approximately 10 events per year as measured by TITAND. Since the total event number is much larger than that of a normal collapse-driven supernova, our results suggest that we will detect more neutrinos from a collapsar in the next generation of neutrino detectors than expected for a normal collapse-driven supernova, and, at the same time, we will observe the remnant of a collapsar naturally with optical telescopes as is the case for supernova. Such results would provide strong evidence for another mechanism of the central engine that is quite different from that of normal collapse-driven supernovae.

A Search for Nontriggered Gamma‐Ray Bursts in the BATSE Database

We describe a search of archival data from the Burst and Transient Source Experiment (BATSE). The purpose of the search is to find astronomically interesting transients that did not activate the burst-detection (or trigger) system on board the spacecraft. Our search is sensitive to events with peak fluxes (on the 1.024 s timescale) that are lower by a factor of approximately 2 than can be detected with the on-board burst trigger. In a search of 345 days of archival data, we detected 91 events in the 50-300 keV range that resemble classical gamma-ray bursts but that did not activate the on-board burst trigger. We also detected 110 low-energy (25-50 keV) events of unknown origin that may include activity from' soft gamma repeater (SGR) 1806-20 and bursts and flares from X-ray binaries. This paper gives the occurrence times, estimated source directions, durations, peak fluxes, and fluences for the 91 gamma-ray burst candidates. The direction and intensity distributions of these bursts imply that the biases inherent in the on-board trigger mechanism have not significantly affected the completeness of the published BATSE gamma-ray burst catalogs.