ABSTRACT
We present the most extensive sample of 45 type I (short) and 275 type II (long) gamma-ray bursts (GRBs) with known redshift to investigate the correlation between the rest-frame peak ...energy, Ep,i and the total isotropic equivalent energy, Eiso of the prompt emission (Amati relation). The Ep,i–Eiso correlation for type I bursts is found to be well distinguished from the one constructed for type II bursts and has a similar power-law index value, Ep,i$\propto E_\text{iso}^{~0.4}$, which possibly indicates the same emission mechanism of both GRB types. We show that the initial pulse complex (IPC) of type I bursts with an extended emission and regular type I bursts follow the same correlation. We obtain similar results for type II bursts associated with Ic supernovae and for regular type II bursts. Three possible outliers from the Ep,i–Eiso correlation for type II subsample are detected. Significant evolution of the Ep,i–Eiso correlation with redshift for type II bursts is not found. We suggest the new classification method, based on the Ep,i–Eiso correlation and introduce two parameters, $EH = E_\text{p,i,2} ~ E_\text{iso,51}^{~-0.4}$ and $EHD = E_\text{p,i,2} ~ E_\text{iso,51}^{~-0.4} ~ T_\text{90,i}^{~-0.5}$, where Ep,i,2 is the value of Ep,i parameter in units of 100 keV, Eiso,51 is the value of Eiso parameter in units of 1051 erg, and T90,i is the rest-frame duration in units of seconds. EHD is found to be the most reliable parameter for the blind type I/type II classification, which can be used to classify GRBs with no redshift.
ABSTRACT
SPI-ACS/INTEGRAL is one of the most sensitive orbital gamma-ray detectors in energy range above 80 keV. Since 2002 it registered several thousands of gamma-ray bursts (GRBs), including the ...bursts associated with LIGO-Virgo gravitational wave events GW 170817 and GW 190425. No dedicated in-flight calibrations were performed for SPI-ACS/INTEGRAL, complicating estimation of spectral and energetic characteristics of an event. Using data of GBM/Fermi we perform cross-calibration of SPI-ACS/INTEGRAL, based on 1032 bright GRBs registered by both experiments. We find the conversion factor between instrumental counts from SPI-ACS and energy units from GBM to be dependent on hardness of GRB spectrum (defined as the characteristic energy value, Ep) and on location of a source in spacecraft-based coordinate system. We determine the corresponding analytical model to calculate the conversion factor and estimate its accuracy empirically. Sensitivity of SPI-ACS/INTEGRAL to detect gamma-ray transients is also investigated. Using the calibration we re-estimate energetics of GRB/GW 190425, detected by SPI-ACS/INTEGRAL alone. We constrain possible range of the characteristic energy Ep and isotropic equivalent of total energy, emitted in gamma-rays Eiso for GRB 190425, using the Ep, i–Eiso (Amati) correlation. The calibration model could be applied to any transients with energy spectrum, analogous to GRBs.
Abstract
Gamma-ray bursts (GRBs) are classified into long and short events. Long GRBs (LGRBs) are associated with the end states of very massive stars, while short GRBs (SGRBs) are linked to the ...merger of compact objects. GRB 200826A was a peculiar event, because by definition it was an SGRB, with a rest-frame duration of ∼0.5 s. However, this event was energetic and soft, which is consistent with LGRBs. The relatively low redshift (
z
= 0.7486) motivated a comprehensive, multiwavelength follow-up campaign to characterize its host, search for a possible associated supernova (SN), and thus understand the origin of this burst. To this aim we obtained a combination of deep near-infrared (NIR) and optical imaging together with spectroscopy. Our analysis reveals an optical and NIR bump in the light curve whose luminosity and evolution are in agreement with several SNe associated to LGRBs. Analysis of the prompt GRB shows that this event follows the
E
p,i
–
E
iso
relation found for LGRBs. The host galaxy is a low-mass star-forming galaxy, typical of LGRBs, but with one of the highest star formation rates, especially with respect to its mass (
log
M
*
/
M
⊙
=
8.6
, SFR ∼ 4.0
M
⊙
yr
−1
). We conclude that GRB 200826A is a typical collapsar event in the low tail of the duration distribution of LGRBs. These findings support theoretical predictions that events produced by collapsars can be as short as 0.5 s in the host frame and further confirm that duration alone is not an efficient discriminator for the progenitor class of a GRB.
We present our observations of electromagnetic transients associated with GW170817/GRB 170817A using optical telescopes of Chilescope observatory and Big Scanning Antenna (BSA) of Pushchino Radio ...Astronomy Observatory at 110 MHz. The Chilescope observatory detected an optical transient of ∼19m on the third day in the outskirts of the galaxy NGC 4993; we continued observations following its rapid decrease. We put an upper limit of 1.5 × 104 Jy on any radio source with a duration of 10-60 s, which may be associated with GW170817/GRB 170817A. The prompt gamma-ray emission consists of two distinctive components-a hard short pulse delayed by ∼2 s with respect to the LIGO signal and softer thermal pulse with T ∼ 10 keV lasting for another ∼2 s. The appearance of a thermal component at the end of the burst is unusual for short GRBs. Both the hard and the soft components do not satisfy the Amati relation, making GRB 170817A distinctively different from other short GRBs. Based on gamma-ray and optical observations, we develop a model for the prompt high-energy emission associated with GRB 170817A. The merger of two neutron stars creates an accretion torus of ∼10−2 M , which supplies the black hole with magnetic flux and confines the Blandford-Znajek-powered jet. We associate the hard prompt spike with the quasispherical breakout of the jet from the disk wind. As the jet plows through the wind with subrelativistic velocity, it creates a radiation-dominated shock that heats the wind material to tens of kiloelectron volts, producing the soft thermal component.
We have analyzed the light curves of 519 short gamma-ray bursts (GRBs) detected in the SPI-ACS/INTEGRAL experiment from December 2002 toMay 2014 to search for precursors (a possible activity of the ...GRB source before the beginning of themain episode). Both the light curves of 519 individual events and the averaged light curve of 372 brightest bursts have been analyzed. In several cases, we have found and thoroughly studied precursor candidates based on SPI-ACS/INTEGRAL, GBM/Fermi, and LAT/Fermi data. A statistical analysis of the averaged light curve for the entire sample of short bursts has revealed no regular precursor. Upper limits for the relative intensity of precursors have been estimated. We have compared our results with those of other authors; no convincing evidence for the existence of precursors of short GRBs has been found. We show that the fraction of short GRBs with precursors is less than 0.4% of all short bursts.
A detailed analysis of the GBM/Fermi experiment data is carried out to classify GRB 200415A. It is shown that, on the one hand, this event exhibits typical for type I (short) gamma-ray bursts (GRBs) ...properties, such as duration, variability, and the character of spectral evolution (lag). On the other hand, the localization of the event source on the celestial plane, obtained by the triangulation method (IPN), indicates the nearby (
Mpc) galaxy NGC 253 (Sculptor) as a possible host galaxy for this burst. It introduces significant restrictions on the energetics of the event (
erg) and gives an alternative interpretation of GRB 200415A as a giant flare (GF) of a soft gamma repeater (SGR). This interpretation is supported by the atypically hard energy spectrum. In addition, according to the position of the burst on the
(the position of the maximum in the energy spectrum
in the source frame depending on the isotropic equivalent of the total energy, emitted in gamma rays) and
(duration in the source frame depending on the combination of parameters
) diagrams, GRB 200415A is unambiguously classified as a giant flare of a magnetar, assuming its association with the galaxy NGC 253. In these diagrams, known giant flares in the Galaxy and candidates for giant flares in nearby galaxies form a well-defined group, which includes the GRB 200415A.
The results of observations of the gravitational-wave (GW) event S190425z recorded by the LIGO/Virgo detectors with the anti-coincidence shield (ACS) of the SPI gamma-ray spectrometer onboard the ...INTEGRAL observatory are presented. With a high probability (
>
99%) it was associated with a neutron star (NS) merger in a close binary system. This is only the second event of such a type in the history of gravitational-wave observations (after GW170817). A weak gamma-ray burst, GRB190425, consisting of two pulses ∼0.5 and ∼5.9 s after the NS merger in the event S190425z with an a priori significance of 3.5 and 4.4
σ
(taken together 5.5
σ
) was detected by SPI-ACS. Analysis of the SPI-ACS count rate history recorded on these days (a total of ∼125 ks of observations) has shown that the rate of random occurrence of two close spikes with the characteristics of GRB190425 does not exceed 6.4 × 10
−5
s
−1
(i.e., such events occur by chance, on average, every ∼4.3 hours). Note that the time profile of GRB190425 has much in common with the profile of GRB170817A accompanying the event GW170817, that both NS mergers were the nearest (≤150 Mpc) of all the events recorded by the LIGO/Virgo detectors, and that no significant excesses of the gamma-ray flux above the background were detected in any of ∼30 black hole merger events recorded to date by these detectors. No bursts of hard radiation were detected in the field of view of the SPI and IBIS/ISGRI gamma-ray telescopes onboard INTEGRAL. This, along with the absence of detection of gamma-ray emission from GRB190425 by the GBM gamma-ray burst monitor of the Fermi observatory suggesting its occultation by the Earth, allows the localization region for the source of this GWevent to be reduced significantly. The parameters
E
iso
and
E
p
for GRB190425 are estimated and compared with those for GRB170817A.
Detection, observation and description of supernovae associated with gamma-ray bursts are currently topical tasks in the field of transient phenomena. From the moment an assumption is made about the ...relationship of the gamma-ray burst with a supernova to obtaining the parameters of the latter, many steps must be taken, and each of them introduces uncertainty and systematics into the final result. In this paper, we analyze the selective effects that arise during the determination of the parameters of supernovae associated with gamma-ray bursts and discuss possible options for taking them into account and minimizing them.
ABSTRACT
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 Tmax) 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 Ep,i = 20.0 ± 8.5 keV and Eiso = (1.1 ± 0.2) × 1050 erg were obtained. According to the position of the burst on the Ep,i–Eiso correlation, GRB 201015A was classified as a type II (long) GRB, which was also confirmed by the T90,i–EH diagram.
PDF
