193 research outputs found
Optical/near-IR observations of Gamma-Ray Bursts in the Afterglow Era
An overview of the optical and near-IR observations of GRBs in the Afterglow
Era is presented, covering the period 1997-2000. They have allowed to a better
understanding of the underlying GRB physics as well as to constraint the
progenitor models.Comment: To appear in the Proceedings of The Second Rome GRB Workshop, ed: N.
Masetti. Springer, in press. Review talk (6 pages, 2 figures
Central Engine Memory of Gamma-Ray Bursts and Soft Gamma-Ray Repeaters
Gamma-ray Bursts (GRBs) are bursts of -rays generated from
relativistic jets launched from catastrophic events such as massive star core
collapse or binary compact star coalescence. Previous studies suggested that
GRB emission is erratic, with no noticeable memory in the central engine. Here
we report a discovery that similar light curve patterns exist within individual
bursts for at least some GRBs. Applying the Dynamic Time Warping (DTW) method,
we show that similarity of light curve patterns between pulses of a single
burst or between the light curves of a GRB and its X-ray flare can be
identified. This suggests that the central engine of at least some GRBs carries
"memory" of its activities. We also show that the same technique can identify
memory-like emission episodes in the flaring emission in Soft Gamma-Ray
Repeaters (SGRs), which are believed to be Galactic, highly magnetized neutron
stars named magnetars. Such a phenomenon challenges the standard black hole
central engine models for GRBs, and suggest a common physical mechanism behind
GRBs and SGRs, which points towards a magnetar central engine of GRBs.Comment: 7 pages, 4 figures, ApJ Letters in pres
Follow-up observations from observatories based in Spain
We present a review of the follow-up observations carried out from
observatories located in Spain; Calar-Alto, Izanha and Roque de Los Muchachos.
It summarizes the observations carried out by our group for 27 GRBs occurred in
the period 1999-2000, spanning from GRB 990123 to GRB 001007.Comment: 3 pages, no figures. To appear in the proceedings of the October 2000
Rome Workshop on ``Gamma-Ray Bursts in the Afterglow Era'
Retrograde versus Prograde Models of Accreting Black Holes
There is a general consensus that magnetic fields, accretion disks, and rotating black holes are instrumental in the generation of the most powerful sources of energy in the known universe. Nonetheless, because magnetized accretion onto rotating black holes involves both the complications of nonlinear magnetohydrodynamics that currently cannot fully be treated numerically, and uncertainties about the origin of magnetic fields that at present are part of the input, the space of possible solutions remains less constrained. Consequently, the literature still bears witness to the proliferation of rather different black hole engine models. But the accumulated wealth of observational data is now sufficient to meaningfully distinguish between them. It is in this light that this critical paper compares the recent retrograde framework with standard "spin paradigm" prograde models
GRB 980425 host: [C II], [O I], and CO lines reveal recent enhancement of star formation due to atomic gas inflow
Context. Accretion of gas from the intergalactic medium is required to fuel star formation in galaxies. We have recently suggested that this process can be studied using host galaxies of gamma-ray bursts (GRBs). Aims. Our aim is to test this possibility by studying in detail the properties of gas in the closest galaxy hosting a GRB (980425). Methods. We obtained the first ever far-infrared (FIR) line observations of a GRB host, namely Herschel/PACS resolved [C ii] 158 μm and [O i] 63 μm spectroscopy, and an APEX/SHeFI CO(2-1) line detection and ALMA CO(1-0) observations of the GRB 980425 host. Results. The GRB 980425 host has elevated [C ii]/FIR and [O i]/FIR ratios and higher values of star formation rates (SFR) derived from line ([C ii], [O i], Hα) than from continuum (UV, IR, radio) indicators. [C ii] emission exhibits a normal morphology, peaking at the galaxy centre, whereas [O i] is concentrated close to the GRB position and the nearby Wolf-Rayet region. The high [O i] flux indicates that there is high radiation field and high gas density at these positions, as derived from modelling of photo-dissociation regions. The [C ii]/CO luminosity ratio of the GRB 980425 host is close to the highest values found for local star-forming galaxies. Indeed, its CO-derived molecular gas mass is low given its SFR and metallicity, but the [C ii]-derived molecular gas mass is close to the expected value. Conclusions. The [O i] and H i concentrations and the high radiation field and density close to the GRB position are consistent with the hypothesis of a very recent (at most a few tens of Myr ago) inflow of atomic gas triggering star formation. In this scenario dust has not had time to build up (explaining high line-to-continuum ratios). Such a recent enhancement of star formation activity would indeed manifest itself in high SFR/SFR ratios because the line indicators are sensitive only to recent (∼ 10 Myr) activity, whereas the continuum indicators measure the SFR averaged over much longer periods (~100 Myr). Within a sample of 32 other GRB hosts, 20 exhibit SFR/SFR> 1 with a mean ratio of 1.74 ± 0.32. This is consistent with a very recent enhancement of star formation that is common among GRB hosts, so galaxies that have recently experienced inflow of gas may preferentially host stars exploding as GRBs. Therefore GRBs may be used to select a unique sample of galaxies that is suitable for the investigation of recent gas accretion.J.L.W. is supported by a European Union COFUND/Durham Junior Research Fellowship under EU grant agreement number 267209, and acknowledges additional support from STFC (ST/L00075X/1). A.K. acknowledges support from the Foundation for Polish Science (FNP) and the Polish National Science Center grant 2013/11/N/ST9/00400. A.J.C.T. acknowledges support from the Spanish Ministry Project AYA2015-71718-R. D.X. acknowledges the support by the One-Hundred-Talent Program of the Chinese Academy of Sciences, and by the Strategic Priority Research Program >Multi-wavelength Gravitational Wave Universe> of the Chinese Academy of Sciences (No. XDB23000000).Peer Reviewe
GRANAT/WATCH catalogue of cosmic gamma-ray bursts: December 1989 to September 1994
We present the catalogue of gamma-ray bursts observed with the WATCH all-sky
monitor on board the GRANAT satellite during the period December 1989 to
September 1994. The cosmic origin of 95 bursts comprising the catalogue is
confirmed either by their localization with WATCH or by their detection with
other GRB experiments. For each burst its time history and information on its
intensity in the two energy ranges 8-20 keV and 20-60 keV are presented. Most
events show hardening of the energy spectrum near the burst peak. In part of
the bursts an X-ray precursor or a tail is seen at 8-20 keV. We have determined
the celestial positions of the sources of 47 bursts. Their localization regions
(at 3-sigma confidence level) are equivalent in area to circles with radii
ranging from 0.2 to 1.6 deg. The burst sources appear isotropically distributed
on the sky on large angular scales.Comment: 18 pages (including 3 tables and 7 figures), LaTeX, l-aa style.
Accepted by Astronomy and Astrophysics Suppl. Serie
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