We report on International Gamma-Ray Astrophysics Laboratory (INTEGRAL) observations of the soft γ-ray repeater SGR 1935+2154 performed between 2020 April 28 and May 3. Several short bursts with ...fluence of erg cm−2 were detected by the Imager on-board INTEGRAL (IBIS) instrument in the 20-200 keV range. The burst with the hardest spectrum, discovered and localized in real time by the INTEGRAL Burst Alert System, was spatially and temporally coincident with a short and very bright radio burst detected by the Canadian Hydrogen Intensity Mapping Experiment (CHIME) and Survey for Transient Astronomical Radio Emission 2 (STARE2) radio telescopes at 400-800 MHz and 1.4 GHz, respectively. Its lightcurve shows three narrow peaks separated by ∼29 ms time intervals, superimposed on a broad pulse lasting ∼0.6 s. The brightest peak had a delay of 6.5 1.0 ms with respect to the 1.4 GHz radio pulse (that coincides with the second and brightest component seen at lower frequencies). The burst spectrum, an exponentially cutoff power law with photon index and peak energy , is harder than those of the bursts usually observed from this and other magnetars. By the analysis of an expanding dust-scattering ring seen in X-rays with the Neil Gehrels Swift Observatory X-ray Telescope (XRT) instrument, we derived a distance of kpc for SGR 1935+2154, independent of its possible association with the supernova remnant G57.2+0.8. At this distance, the burst 20-200 keV fluence of erg cm−2 corresponds to an isotropic emitted energy of erg. This is the first burst with a radio counterpart observed from a soft γ-ray repeater and it strongly supports models based on magnetars that have been proposed for extragalactic fast radio bursts.
We present the fourth in a series of catalogs of gamma-ray bursts (GRBs) observed with Fermi's Gamma-ray Burst Monitor (Fermi-GBM). It extends the six year catalog by four more years, now covering ...the 10 year time period from trigger enabling on 2008 July 12 to 2018 July 11. During this time period GBM triggered almost twice a day on transient events, 2356 of which we identified as cosmic GRBs. Additional trigger events were due to solar flare events, magnetar burst activities, and terrestrial gamma-ray flashes. The intention of the GBM GRB catalog series is to provide updated information to the community on the most important observables of the GBM-detected GRBs. For each GRB the location and main characteristics of the prompt emission, the duration, peak flux, and fluence are derived. The latter two quantities are calculated for the 50-300 keV energy band, where the maximum energy release of GRBs in the instrument reference system is observed and also for a broader energy band from 10-1000 keV, exploiting the full energy range of GBM's low-energy detectors. Furthermore, information is given on the settings of the triggering criteria and exceptional operational conditions during years 7 to 10 in the mission. This fourth catalog is an official product of the Fermi-GBM science team, and the data files containing the complete results are available from the High-Energy Astrophysics Science Archive Research Center.
On 2017 August 17 at 12:41:06 UTC the Fermi Gamma-ray Burst Monitor (GBM) detected and triggered on the short gamma-ray burst (GRB) 170817A. Approximately 1.7 s prior to this GRB, the Laser ...Interferometer Gravitational-wave Observatory triggered on a binary compact merger candidate associated with the GRB. This is the first unambiguous coincident observation of gravitational waves and electromagnetic radiation from a single astrophysical source and marks the start of gravitational-wave multi-messenger astronomy. We report the GBM observations and analysis of this ordinary short GRB, which extraordinarily confirms that at least some short GRBs are produced by binary compact mergers.
The capability of the Fermi Gamma-ray Burst Monitor (GBM) to localize gamma-ray bursts (GRBs) is evaluated for two different automated algorithms: the GBM Team's RoboBA algorithm and the ...independently developed BALROG algorithm. Through a systematic study utilizing over 500 GRBs with known locations from instruments like Swift and the Fermi Large Area Telescope, we directly compare the effectiveness of, and accurately estimate the systematic uncertainty for, both algorithms. We show that simple adjustments to the GBM Team's RoboBA, in operation since early 2016, yield significant improvement in the systematic uncertainty, removing the long tail identified in the systematic, and improve the overall accuracy. The systematic uncertainty for the updated RoboBA localizations is 1 8 for 52% of GRBs and 4 1 for the remaining 48%. Both from public reporting by BALROG and our systematic study, we find the systematic uncertainty of 1°-2° quoted in circulars for bright GRBs is an underestimate of the true magnitude of the systematic, which we find to be 2 7 for 74% of GRBs and 33° for the remaining 26%. We show that, once the systematic uncertainty is considered, the RoboBA 90% localization confidence regions can be more than an order of magnitude smaller in area than those produced by BALROG.
The Gamma‐ray Burst Monitor (GBM) on the Fermi Gamma‐ray Space Telescope detected 12 intense terrestrial gamma ray flashes (TGFs) during its first year of observation. Typical maximum energies for ...most of the TGFs are ∼30 MeV, with one TGF having a 38 MeV photon; two of the TGFs are softer and longer than the others. After correcting for instrumental effects, a representative bright TGF is found to have a fluence of ∼0.7 photons cm−2. Pulses are either symmetrical or have faster risetimes than fall times; they are well fit with Gaussian or lognormal functions. The fastest risetime observed was 7 μs, constraining the source radius to be less than about 2 km from the velocity of light. TGFs with multiple pulses separated in time have been known since their discovery; the GBM sample also includes clear cases of partially overlapping pulses. Four TGFs are associated with lightning locations from the World Wide Lightning Location Network. With the several μs absolute time accuracy of GBM, the time order can be confidently identified: one TGF occurred before the lightning, two were simultaneous, and one TGF occurred after the lightning.
Abstract
We present the systematic spectral analyses of gamma-ray bursts (GRBs) detected by the Fermi Gamma-Ray Burst Monitor during its first ten years of operation. This catalog contains two types ...of spectra: time-integrated spectral fits and spectral fits at the brightest time bin, from 2297 GRBs, resulting in a compendium of over 18,000 spectra. The four different spectral models used for fitting the spectra were selected based on their empirical importance to the shape of many GRBs. We describe in detail our procedure and criteria for the analyses, and present the bulk results in the form of parameter distributions both in the observer frame and in the GRB rest frame. 941 GRBs from the first four years have been refitted using the same methodology as that of the 1356 GRBs in years five through ten. The data files containing the complete results are available from the High-Energy Astrophysics Science Archive Research Center.
ABSTRACT Using observations of the INTErnational Gamma-Ray Astrophysics Laboratory (INTEGRAL), we place upper limits on the gamma-ray and hard X-ray prompt emission associated with the gravitational ...wave event GW150914, which was discovered by the LIGO/Virgo Collaboration. The omnidirectional view of the INTEGRAL/SPI-ACS has allowed us to constrain the fraction of energy emitted in the hard X-ray electromagnetic component for the full high-probability sky region of LIGO triggers. Our upper limits on the hard X-ray fluence at the time of the event range from erg cm−2 to erg cm−2 in the 75 keV-2 MeV energy range for typical spectral models. Our results constrain the ratio of the energy promptly released in gamma-rays in the direction of the observer to the gravitational wave energy E E . We discuss the implication of gamma-ray limits for the characteristics of the gravitational wave source, based on the available predictions for prompt electromagnetic emission.
We examine a sample of 2301 gamma-ray bursts, detected by Konus-Wind in the triggered mode between 1994 and 2017 and localized by the interplanetary network (IPN), for evidence of gravitational ...lensing. We utilize all the available gamma-ray burst (GRB) data: time histories, localizations, and energy spectra. We employ common IPN techniques to find and quantify similarities in the light curves of 2,646,150 burst pairs, and for the pairs with significant similarities, we examine their IPN localizations to determine whether they are consistent with a common origin. For pairs that are consistent, we derive and compare energy spectra, and compute a figure of merit that allows us to compare and rank burst pairs. We conduct both a blind search, between all possible burst pairs, and a targeted search, between pairs in which one burst has both a spectroscopic redshift and an identification of an intervening system, as measured by one or more lower spectroscopic redshifts. We identify six pairs in the blind search that could be taken as evidence for lensing, but none are compelling enough to claim a detection with good confidence. No candidates were detected in the targeted search. For our GRB sample, we set an upper limit to the optical depth to lensing of 0.0033, which is comparable to that of optical sources. We conclude that proposed scenarios in which a large fraction of the GRB population is lensed are extremely unlikely.
Soft γ-ray repeaters exhibit bursting emission in hard X-rays and soft γ-rays. During the active phase, they emit random short (milliseconds to several seconds long), hard-X-ray bursts, with peak ...luminosities
of 10
to 10
erg per second. Occasionally, a giant flare with an energy of around 10
to 10
erg is emitted
. These phenomena are thought to arise from neutron stars with extremely high magnetic fields (10
to 10
gauss), called magnetars
. A portion of the second-long initial pulse of a giant flare in some respects mimics short γ-ray bursts
, which have recently been identified as resulting from the merger of two neutron stars accompanied by gravitational-wave emission
. Two γ-ray bursts, GRB 051103 and GRB 070201, have been associated with giant flares
. Here we report observations of the γ-ray burst GRB 200415A, which we localized to a 20-square-arcmin region of the starburst galaxy NGC 253, located about 3.5 million parsecs away. The burst had a sharp, millisecond-scale hard spectrum in the initial pulse, which was followed by steady fading and softening over 0.2 seconds. The energy released (roughly 1.3 × 10
erg) is similar to that of the superflare
from the Galactic soft γ-ray repeater SGR 1806-20 (roughly 2.3 × 10
erg). We argue that GRB 200415A is a giant flare from a magnetar in NGC 253.
In light of the joint multimessenger detection of a binary neutron star merger as the gamma-ray burst GRB 170817A and in gravitational waves as GW170817, we reanalyze the Fermi Gamma-ray Burst ...Monitor data of one of the closest short gamma-ray bursts (SGRBs): GRB 150101B. We find that this burst is composed of a short hard spike followed by a comparatively long soft tail. This apparent two-component nature is phenomenologically similar to that of GRB 170817A. While GRB 170817A was distinct from the previously known population of SGRBs in terms of its prompt intrinsic energetics, GRB 150101B is not. Despite these differences, GRB 150101B can be modeled as a more on-axis version of GRB 170817A. Identifying a similar signature in two of the closest SGRBs suggests that the soft tail is common, but generally undetectable in more distant events. If so, it will be possible to identify nearby SGRBs from the prompt gamma-ray emission alone, aiding the search for kilonovae.
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