GRB 130925A was an unusual gamma ray burst (GRB), consisting of three distinct episodes of high-energy emission spanning ∼20 ks, making it a member of the proposed category of ‘ultralong’ bursts. It ...was also unusual in that its late-time X-ray emission observed by Swift was very soft, and showed a strong hard-to-soft spectral evolution with time. This evolution, rarely seen in GRB afterglows, can be well modelled as the dust-scattered echo of the prompt emission, with stringent limits on the contribution from the normal afterglow (i.e. external shock) emission. We consider and reject the possibility that GRB 130925A was some form of tidal disruption event, and instead show that if the circumburst density around GRB 130925A is low, the long duration of the burst and faint external shock emission are naturally explained. Indeed, we suggest that the ultralong GRBs as a class can be explained as those with low circumburst densities, such that the deceleration time (at which point the material ejected from the nascent black hole is decelerated by the circumburst medium) is ∼20 ks, as opposed to a few hundred seconds for the normal long GRBs. The increased deceleration radius means that more of the ejected shells can interact before reaching the external shock, naturally explaining both the increased duration of GRB 130925A, the duration of its prompt pulses, and the fainter-than-normal afterglow.
Wide-field surveys are discovering a growing number of rare transients whose physical origin is not yet well understood. Here we present optical and UV data and analysis of intermediate Palomar ...Transient Factory (iPTF) 16asu, a luminous, rapidly evolving, high-velocity, stripped-envelope supernova (SN). With a rest-frame rise time of just four days and a peak absolute magnitude of mag, the light curve of iPTF 16asu is faster and more luminous than that of previous rapid transients. The spectra of iPTF 16asu show a featureless blue continuum near peak that develops into an SN Ic-BL spectrum on the decline. We show that while the late-time light curve could plausibly be powered by 56Ni decay, the early emission requires a different energy source. Nondetections in the X-ray and radio strongly constrain the energy coupled to relativistic ejecta to be at most comparable to the class of low-luminosity gamma-ray bursts (GRBs). We suggest that the early emission may have been powered by either a rapidly spinning-down magnetar or by shock breakout in an extended envelope of a very energetic explosion. In either scenario a central engine is required, making iPTF 16asu an intriguing transition object between superluminous SNe, SNe Ic-BL, and low-luminosity GRBs.
We present X-ray and radio observations of the Fast Blue Optical Transient CRTS-CSS161010 J045834−081803 (CSS161010 hereafter) at t = 69-531 days. CSS161010 shows luminous X-ray (Lx ∼ 5 × 1039 erg ...s−1) and radio (L ∼ 1029 erg s−1 Hz−1) emission. The radio emission peaked at ∼100 days post-transient explosion and rapidly decayed. We interpret these observations in the context of synchrotron emission from an expanding blast wave. CSS161010 launched a mildly relativistic outflow with velocity Γβc ≥ 0.55c at ∼100 days. This is faster than the non-relativistic AT 2018cow (Γβc ∼ 0.1c) and closer to ZTF18abvkwla (Γβc ≥ 0.3c at 63 days). The inferred initial kinetic energy of CSS161010 (Ek 1051 erg) is comparable to that of long gamma-ray bursts, but the ejecta mass that is coupled to the mildly relativistic outflow is significantly larger ( ). This is consistent with the lack of observed γ-rays. The luminous X-rays were produced by a different emission component to the synchrotron radio emission. CSS161010 is located at ∼150 Mpc in a dwarf galaxy with stellar mass M* ∼ 107 M and specific star formation rate sSFR ∼ 0.3 Gyr−1. This mass is among the lowest inferred for host galaxies of explosive transients from massive stars. Our observations of CSS161010 are consistent with an engine-driven aspherical explosion from a rare evolutionary path of a H-rich stellar progenitor, but we cannot rule out a stellar tidal disruption event on a centrally located intermediate-mass black hole. Regardless of the physical mechanism, CSS161010 establishes the existence of a new class of rare (rate < 0.4% of the local core-collapse supernova rate) H-rich transients that can launch mildly relativistic outflows.
ABSTRACT In this catalog, we present the results of a systematic study of 295 short gamma-ray bursts (GRBs) detected by Konus-Wind (KW) from 1994 to 2010. From the temporal and spectral analyses of ...the sample, we provide the burst durations, the spectral lags, the results of spectral fits with three model functions, the total energy fluences, and the peak energy fluxes of the bursts. We discuss evidence found for an additional power-law spectral component and the presence of extended emission in a fraction of the KW short GRBs. Finally, we consider the results obtained in the context of the Type I (merger-origin)/Type II (collapsar-origin) classifications.
The most energetic gamma-ray bursts (GRBs) are remarkable sources releasing huge amounts of energy on short timescales. Their prompt emission, which usually lasts a few seconds, is so bright that it ...is visible across the whole observable universe. Studying these extreme events may provide clues on the nature of GRB progenitors and on the physical processes at work in relativistic jets. In this paper, we study the bright end of the isotropic energy distribution of long GRBs. We use two samples of long GRBs with redshift detected by Fermi/GBM or Konus-Wind, two instruments that measure the spectral shape and the energetics of the prompt emission accurately. We focus on GRBs within a range of redshifts z = 1-5, a volume that contains a large number of energetic GRBs, and we propose a simple method to reconstruct the bright end of the GRB energy distribution from the observed one. We find that the GRB energy distribution cannot be described by a simple power law but requires a strong cutoff above 1 - 3 × 10 54 erg. We attribute this feature to an intrinsic limit on the energy per unit of solid angle radiated by GRBs.
We report on the bright burst detected by four Interplanetary network (IPN) spacecraft on 2015 April 12. The IPN localization of the source is consistent with the position of the recently discovered ...soft gamma-repeater SGR 1935+2154. From the Konus-Wind (KW) observation, we derive temporal and spectral parameters of the emission, and the burst energetics. The rather long duration of the burst (~1.7 s) and the large measured energy fluence (~2.5 x 10 super( -5) erg cm super( -2)) put it in the class of rare 'intermediate' soft gamma-repeater (SGR) flares, and this is the first one observed from SGR 1935+2154. A search for quasi-periodic oscillations in the KW light curve yields no statistically significant signal. Of four spectral models tested, optically thin thermal bremsstrahlung and a single blackbody (BB) function can be rejected on statistical grounds; two more complex models, a cutoff power law (CPL) and a sum of two BB functions (2BB), fit the burst spectra well and neither of them may be ruled out by the KW observation. The CPL and 2BB model parameters we report for this bright flare are typical of SGRs; they are also consistent with those obtained from observations of much weaker and shorter SGR 1935+2154 bursts with other instruments. From the distribution of 2BB spectral fit parameters we estimate the SGR 1935+2154 distance to be <10.0 kpc, in agreement with that of the Galactic supernova remnant G57.2+0.8 at 9.1 kpc.
Context. Gamma-ray bursts (GRBs) occurring in the local Universe constitute an interesting sub-class of the GRB family, since their luminosity is on average lower than that of their cosmological ...analogs. Attempts to understand in a global way this peculiar behaviour is still not possible, since the sample of low redshift GRBs is small, and the properties of individual objects are too different from each other. In addition, their closeness (and consequently high fluxes) make these sources ideal targets for extensive follow-up even with small telescopes, considering also that these GRBs are conclusively associated with supernova (SN) explosions. Aims. We aim to contribute to the study of local bursts by reporting the case of GRB 171205A. This source was discovered by Swift Burst Alert Telescope (BAT) on 2017, December 5 and soon associated with a low redshift host galaxy (z = 0.037), and an emerging SN (SN 2017iuk). Methods. We analyzed the full Swift dataset, comprising the UV-Optical Telescope (UVOT), X-ray Telescope (XRT) and BAT data. In addition, we employed the Konus-Wind high energy data as a valuable extension at γ-ray energies. Results. The photometric SN signature is clearly visible in the UVOT u, b and ν filters. The maximum emission is reached at ∼13 (rest frame) days, and the whole bump resembles that of SN 2006aj, but lower in magnitude and with a shift in time of +2 d. A prebump in the ν-band is also clearly visible, and this is the first time that such a feature is not observed achromatically in GRB–SNe. Its physical origin cannot be easily explained. The X-ray spectrum shows an intrinsic Hydrogen column density NH,int = 7.4+4.1−3.6 × 1020 N H , int = 7 . 4 − 3.6 + 4.1 × 10 20 $ N_{\mathrm{H,int}} = 7.4^{+4.1}_{-3.6}\times 10^{20} $ cm−2, which is at the low end of the N H, int, even considering just low redshift GRBs. The spectrum also features a thermal component, which is quite common in GRBs associated with SNe, but whose origin is still a matter of debate. Finally, the isotropic energy in the γ-ray band, Eiso = 2.18+0.63−5.0 × 1049 E iso = 2 . 18 − 0.50 + 0.63 × 10 49 $ E_{\mathrm{iso}} = 2.18^{+0.63}_{-0.50} \times 10^{49} $ erg, is lower than those of cosmological GRBs. Combining this value with the peak energy in the same band, Ep = 125+141−37 E p = 125 − 37 + 141 $ E_{\mathrm{p}}=125^{+141}_{-37} $ keV, implies that GRB 171205A is an outlier of the Amati relation, as are some other low redshift GRBs, and its emission mechanism should be different from that of canonical, farther away GRBs.
The knowledge of the rate of soft gamma-ray repeater (SGR) giant flares (GFs) is important for understanding the GF mechanism and the SGR energy budget in the framework of the magnetar model. We ...estimate the upper limit to the rate using the results of an extensive search for extragalactic SGR GFs among 140 short gamma-ray bursts detected between 1994 and 2010 by Konus-WIND using Interplanetary Network (IPN) localizations and temporal parameters. We show that Konus-WIND and the IPN are capable of detecting GFs with energies of 2.3 × 1046 erg (which is the energy of the GF from SGR 1806−20 assuming a distance of 15 kpc) at distances of up to ∼30 Mpc and GFs with energies of ≲ 1045 erg (which is the energy of the GF from SGR 0526−66) at distances of up to ≈6 Mpc. Using a sample of 1896 nearby galaxies, we found that only two bursts, GRB 051103 and GRB 070201, have a low chance coincidence probability between an IPN localization and a nearby galaxy. We found the upper limit to the fraction of GFs among short gamma-ray bursts with fluence above ∼5 × 10−7 erg cm−2 to be <8 per cent (95 per cent confidence level). Assuming that the number of active SGRs in nearby galaxies is proportional to their core-collapse supernova rate, we derived the one-sided 95 per cent upper limit to the rate of GFs with energy output similar to the GF from SGR 1806−20 to be
$(0.6\textrm {-}1.2)\times 10^{-4} Q_{46}^{-1.5}$
yr−1 per SGR, where Q
46 is the GF energy output in 1046 erg.
Abstract
We report on Konus-WIND (KW) and Mikhail Pavlinsky Astronomical Roentgen Telescope – X-ray Concentrator (ART-XC) observations and analysis of a nearby GRB 221009A, the brightest
γ
-ray burst ...(GRB) detected by KW for >28 yr of observations. The prompt, pulsed phase of the burst emission lasts for ∼600 s and is followed by a steady power-law decay lasting for more than 25 ks. From the analysis of the KW and ART-XC light curves and the KW spectral data, we derive time-averaged spectral peak energy of the burst
E
p
≈ 2.6 MeV,
E
p
at the brightest emission peak ≈ 3.0 MeV, the total 20 keV–10 MeV energy fluence of ≈0.22 erg cm
−2
, and the peak energy flux in the same band of ≈0.031 erg cm
−2
s
−1
. The enormous observed fluence and peak flux imply, at redshift
z
= 0.151, huge values of isotropic energy release
E
iso
≈ 1.2 × 10
55
erg (or ≳6.5 solar rest mass) and isotropic peak luminosity
L
iso
≈ 3.4 × 10
54
erg s
−1
(64 ms scale), making GRB 221009A the most energetic and one of the most luminous bursts observed since the beginning of the GRB cosmological era in 1997. The isotropic energetics of the burst fit nicely both “Amati” and “Yonetoku” hardness–intensity correlations for >300 KW long GRBs, implying that GRB 221009A is most likely a very hard, super-energetic version of a “normal” long GRB.
Cosmological gamma-ray bursts (GRBs) are known to arise from distinct progenitor channels: short GRBs mostly from neutron star mergers and long GRBs from a rare type of core-collapse supernova (CCSN) ...called collapsars. Highly magnetized neutron stars called magnetars also generate energetic, short-duration gamma-ray transients called magnetar giant flares (MGFs). Three have been observed from the Milky Way and its satellite galaxies, and they have long been suspected to constitute a third class of extragalactic GRBs. We report the unambiguous identification of a distinct population of four local (<5 Mpc) short GRBs, adding GRB 070222 to previously discussed events. While identified solely based on alignment with nearby star-forming galaxies, their rise time and isotropic energy release are independently inconsistent with the larger short GRB population at >99.9% confidence. These properties, the host galaxies, and non-detection in gravitational waves all point to an extragalactic MGF origin. Despite the small sample, the inferred volumetric rates for events above 4 × 10(exp 44) erg of R(sub MGF) =3.8(sup +4.0)(sub -3.1) ×10(exp 5) Gpc(exp -3) yr(exp -1) make MGFs the dominant gamma-ray transient detected from extragalactic sources. As previously suggested, these rates imply that some magnetars produce multiple MGFs, providing a source of repeating GRBs. The rates and host galaxies favor common CCSN as key progenitors of magnetars.
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