549 research outputs found
The optical afterglows and host galaxies of three short/hard gamma-ray bursts
Short GRBs are commonly thought to originate from the merging of double
compact object binaries but direct evidence for this scenario is still missing.
Optical observations of short GRBs allow us to measure redshifts, firmly
identify host galaxies, characterize their properties, and accurately localize
GRBs within them. Multiwavelength observations of GRB afterglows provide useful
information on the emission mechanisms at work. These are all key issues that
allow one to discriminate among different models of these elusive events. We
carried out photometric observations of the short/hard GRB 051227, GRB 061006,
and GRB 071227 with the ESO-VLT starting from several hours after the explosion
down to the host galaxy level several days later. For GRB 061006 and GRB 071227
we also obtained spectroscopic observations of the host galaxy. We compared the
results obtained from our optical observations with the available X-ray data of
these bursts. For all the three above bursts, we discovered optical afterglows
and firmly identified their host galaxies. About half a day after the burst,
the optical afterglows of GRB 051227 and GRB 061006 present a decay
significatly steeper than in the X-rays. In the case of GRB 051227, the optical
decay is so steep that it likely indicates different emission mechanisms in the
two wavelengths ranges. The three hosts are blue, star forming galaxies at
moderate redshifts and with metallicities comparable to the Solar one. The
projected offsets of the optical afterglows from their host galaxies centers
span a wide range, but all afterglows lie within the light of their hosts and
present evidence for local absorption in their X-ray spectra. We discuss our
findings in light of the current models of short GRB progenitors.Comment: Accepted for publication by A&A. 11 pages, 9 figures; v2: minor
changes and new version of Fig.
A nearby GRB host prototype for z~7 Lyman-break galaxies: Spitzer-IRS and X-shooter spectroscopy of the host galaxy of GRB031203
Gamma-ray burst (GRB) host galaxies have been studied extensively in optical
photometry and spectroscopy. Here we present the first mid-infrared spectrum of
a GRB host, HG031203. It is one of the nearest GRB hosts at z=0.1055, allowing
both low and high-resolution spectroscopy with Spitzer-IRS. Medium resolution
UV-to-K-band spectroscopy with the X-shooter spectrograph on the VLT is also
presented, along with Spitzer IRAC and MIPS photometry, as well as radio and
sub-mm observations. These data allow us to construct a UV-to-radio spectral
energy distribution with almost complete spectroscopic coverage from 0.3-35
micron of a GRB host galaxy for the first time, potentially valuable as a
template for future model comparisons. The IRS spectra show strong,
high-ionisation fine structure line emission indicative of a hard radiation
field in the galaxy, suggestive of strong ongoing star-formation and a very
young stellar population. The selection of HG031203 via the presence of a GRB
suggests that it might be a useful analogue of very young star-forming galaxies
in the early universe, and hints that local BCDs may be used as more reliable
analogues of star-formation in the early universe than typical local
starbursts. We look at the current debate on the ages of the dominant stellar
populations in z~7 and z~8 galaxies in this context. The nebular line emission
is so strong in HG031203, that at z~7, it can reproduce the spectral energy
distributions of z-band dropout galaxies with elevated IRAC 3.6 and 4.5 micron
fluxes without the need to invoke a 4000A break.Comment: Published in ApJ. 9 pages, 6 figures, emulateapj styl
SN 2002lt and GRB 021211: a SN/GRB Connection at z = 1
We present spectroscopic and photometric observations of the afterglow of GRB
021211 and the discovery of its associated supernova, SN 2002lt. The spectrum
shows a broad feature (FWHM = 150 A), around 3770 A (in the rest-frame of the
GRB), which we interpret as Ca H+K blueshifted by 14400 km/s. Potential sources
of contamination due to the host galaxy and/or residuals of telluric absorption
have been analyzed and ruled out. Overall, the spectrum shows a suggestive
resemblance with the one of the prototypical type-Ic SN 1994I. This might
indicate that GRBs are produced also by standard type-Ic supernovae.Comment: 6 pages, 5 color figures. Proceedings of the 2003 GRB Conference
(Santa Fe, NM, 2003 Sep 8-12). Needs aipprocs LaTeX clas
The Spectral Lag of GRB060505: A Likely Member of the Long Duration Class
Two long gamma-ray bursts, GRB 060505 and GRB 060614, occurred in nearby
galaxies at redshifts of 0.089 and 0.125 respectively. Due to their proximity
and durations, deep follow-up campaigns to search for supernovae (SNe) were
initiated. However none were found in either case, to limits more than two
orders of magnitude fainter than the prototypical GRB-associated SN, 1998bw. It
was suggested that the bursts, in spite of their durations (4 and 102 s),
belonged to the population of short GRBs which has been shown to be unrelated
to SNe. In the case of GRB 060614 this argument was based on a number of
indicators, including the negligible spectral lag, which is consistent with
that of short bursts. GRB 060505 has a shorter duration, but no spectral lag
was measured. We present the spectral lag measurements of GRB 060505 using
Suzakus Wide Area Monitor and the Swift Burst Alert Telescope. We find that the
lag is 0.36+/- 0.05 s, inconsistent with the lags of short bursts and
consistent with the properties of long bursts and SN-GRBs. These results
support the association of GRB 060505 with other low-luminosity GRBs also found
in star-forming galaxies and indicates that at least some massive stars may die
without bright SNe.Comment: Accepted by ApJL, 5 pages, 3 Figure
Improved constant-frequency hysteresis current control of VSI inverters with simple feedforward bandwidth prediction
GRB 130427A Afterglow: A Test for GRB Models
Gamma-ray Burst 130427A had the largest fluence for almost 30 years. With an isotropic energy output of 8.5×1053 erg and redshift of 0.34, it combined a very high energy release with a relative proximity to Earth in an unprecedented fashion. Sensitive X-ray facilities such as {\it XMM-Newton} and {\it Chandra} detected the afterglow of this event for a record-breaking baseline of 90 Ms. We show the X-ray light curve of GRB 130427A of this event over such an interval. The light curve shows an unbroken power law decay with a slope of α=1.31 over more than three decades in time. In this presentation, we investigate the consequences of this result for the scenarios proposed to interpret GRB 130427A and the implications in the context of the forward shock model (jet opening angle, energetics, surrounding medium). We also remark the chance of extending GRB afterglow observations for several hundreds of Ms with {\it Athena}
- …