Abstract:The short duration (T 90 < 2 s) gamma-ray bursts (GRBs) detected in the SPI-ACS experiment onboard the INTEGRAL observatory are investigated. Averaged light curves have been constructed for various groups of events, including short GRBs and unidentified short events. Extended emission has been found in the averaged light curves of both short GRBs and unidentified short events. It is shown that the fraction of the short GRBs in the total number of SPI-ACS GRBs can range from 30 to 45%, which is considerably lar… Show more
“…The duration, T 90 , of the IPC of the short burst is usually less than ∼2 s. However, for the sum of the light curves of many short bursts, aligned relative to the main peak of the IPC, significant EE has been observed up to ∼100 s in different experiments and for different energy bands, in particular for BATSE 25–110 keV (Lazzati, Ramirez‐Ruiz & Ghisellini 2001) and 50–300 keV (Connaughton 2002; see Fig. 1), BeppoSax 40–700 keV (Montanari et al 2005), KONUS 20–750 keV (Frederiks et al 2004) and the SPI‐anticoincidence shield (ACS) >80 keV (Minaev, Pozanenko & Loznikov 2009, 2010). Indeed, the T 90 parameter of each short burst to be summed is less than ∼2 s. The intensity of the EE seems to depend on the energy band being smaller when increasing the energy band, and on the fluence ratio of the EE episode and the IPC being less than 1/100.…”
The existence of extended emission (EE) is an intriguing property of short‐duration gamma‐ray bursts, because the nature of the EE is still unclear. It might be a rising X‐ray afterglow, or it could be a manifestation of the prolonged activity of a central engine. We consider short‐duration gamma‐ray bursts, emphasizing the common properties of both short bursts and short bursts with EE. Assuming that the EE with broad dynamic range is a common property of short bursts, we propose a two jet model which can describe both short main episode of hard spectra emission, specific for short bursts, and softer spectra EE by different off axis position of observer. The model involves a short‐duration jet, which is powered by heating due to annihilation, and a long‐lived Blandford–Znajek jet with a significantly narrow opening angle. Our proposed model is a plausible mechanism for short‐duration burst energization. It can explain short bursts both with and without EE within a single class of progenitor.
“…The duration, T 90 , of the IPC of the short burst is usually less than ∼2 s. However, for the sum of the light curves of many short bursts, aligned relative to the main peak of the IPC, significant EE has been observed up to ∼100 s in different experiments and for different energy bands, in particular for BATSE 25–110 keV (Lazzati, Ramirez‐Ruiz & Ghisellini 2001) and 50–300 keV (Connaughton 2002; see Fig. 1), BeppoSax 40–700 keV (Montanari et al 2005), KONUS 20–750 keV (Frederiks et al 2004) and the SPI‐anticoincidence shield (ACS) >80 keV (Minaev, Pozanenko & Loznikov 2009, 2010). Indeed, the T 90 parameter of each short burst to be summed is less than ∼2 s. The intensity of the EE seems to depend on the energy band being smaller when increasing the energy band, and on the fluence ratio of the EE episode and the IPC being less than 1/100.…”
The existence of extended emission (EE) is an intriguing property of short‐duration gamma‐ray bursts, because the nature of the EE is still unclear. It might be a rising X‐ray afterglow, or it could be a manifestation of the prolonged activity of a central engine. We consider short‐duration gamma‐ray bursts, emphasizing the common properties of both short bursts and short bursts with EE. Assuming that the EE with broad dynamic range is a common property of short bursts, we propose a two jet model which can describe both short main episode of hard spectra emission, specific for short bursts, and softer spectra EE by different off axis position of observer. The model involves a short‐duration jet, which is powered by heating due to annihilation, and a long‐lived Blandford–Znajek jet with a significantly narrow opening angle. Our proposed model is a plausible mechanism for short‐duration burst energization. It can explain short bursts both with and without EE within a single class of progenitor.
“…The burst onset is delayed to GW trigger to 2 s. A third-order polynomial model was used to fit background signal in time intervals (−118, −30) s and (300, 900) s (data before −118 s are not available). We found for GRB 170817A that there is a deviation of SPI-ACS count statistics from Poisson distribution with a factor of 1.26 (see, e.g., Minaev et al 2010a;Minaev & Pozanenko 2017). Statistical uncertainties for SPI-ACS data were estimated, taking into account the factor of deviation.…”
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 ∼ 19 m 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 × 10 4 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 seconds with respect to the LIGO signal and softer thermal pulse with T ∼ 10 keV lasting for another ∼ 2 seconds. 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 BlandfordZnajek-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.
“…The shower particles also could not be responsible for the second-long afterglow shown in Fig. 1, as highlighted by Minaev et al (2010).…”
Section: The Nature Of the Short Spikesmentioning
confidence: 71%
“…At the same time, we show that the instrument effects of the ACS, the decay of cosmic ray induced radioactivity in BGO crystals, produces the "afterglow" of the spikes discussed by Minaev et al (2010). The detailed knowledge of properties of the spikes allows us to fully characterize them and to separate them from the real GRBs in our analysis.…”
Section: Introductionmentioning
confidence: 95%
“…Instead, Deluit et al (2004) have advanced a hypothesis of possible existence of real very short GRBs missed by the other instruments. Later, Minaev et al (2010) stacked the profiles of a sample of unidentified short bursts in the SPI-ACS and found a weak but recognizable afterglow of the duration of more than a second. They interpreted this observation as an evidence in favor of the hypothesis of the association of the (fraction of) spikes with the real short GRBs.…”
Aims. We study timing properties of a large sample of gamma-ray bursts (GRB) detected by the anti-coincidence shield (ACS) of the SPI spectrometer of INTEGRAL telescope. Methods. We identify GRB-like events in the SPI-ACS data. The data set under investigation is the history of count rate of the SPI-ACS detector recorded with a binning of 50 ms over the time span of ∼10 yr. In spite of the fact that SPI-ACS does not have imaging capability, it provides high statistics signal for each GRB event, because of its large effective area.Results. We classify all isolated excesses in the SPI-ACS count rate into three types: short spikes produced by cosmic rays, GRBs and Solar flare induced events. We find some ∼1500 GRB-like events in the 10 yr exposure. A significant fraction of the GRB-like events identified in SPI-ACS occur in coincidence with triggers of other gamma-ray telescopes and could be considered as confirmed GRBs. We study the distribution of durations of the GRBs detected by SPI-ACS and find that the peak of the distribution of long GRBs is at 20 s, i.e. somewhat shorter than for the long GRBs detected by BATSE. Contrary to the BATSE observation, the population of short GRBs does not have any characteristic timescale. Instead, the distribution of durations extends as a powerlaw to the shortest timescale accessible for SPI-ACS, ≤50 ms. We also find that a large fraction of long GRBs has a characteristic variability timescale of the order of 1 s. We discuss the possible origin of this timescale.
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