72 research outputs found
A Direct Measurement of the Dust Extinction Curve in an Intermediate-Redshift Galaxy
We present a proof-of-concept study that dust extinction curves can be
extracted from the infrared (IR), optical, ultraviolet (UV) and X-ray afterglow
observations of GRBs without assuming known extinction laws. We focus on GRB
050525A (z = 0.606), for which we also present IR observations from the Spitzer
Space Telescope at about 2.3 days post-burst. We construct the spectral energy
distribution (SED) of the afterglow and use it to derive the dust extinction
curve of the host galaxy in 7 optical/UV wavebands. By comparing our derived
extinction curve to known templates, we see that the Galactic or Milky Way
extinction laws are disfavored versus the Small and Large Magellanic Cloud (SMC
and LMC) ones, but that we cannot rule out the presence of a LMC-like 2175
angstrom bump in our extinction curve. The dust-to-gas ratio present within the
host galaxy of GRB 050525A is similar to that found in the LMC, while about 10
to 40% more dust is required if the SMC template is assumed. Our method is
useful to observatories that are capable of simultaneously observing GRB
afterglows in multiple wavebands from the IR to the X-ray.Comment: 9 pages, 5 figures. Accepted by ApJ. Minor changes to 2nd Paragraph
of Introductio
The Optical Afterglow of GRB 011211
We present early-time optical photometry and spectroscopy of the optical
afterglow of the gamma-ray burst GRB 011211. The spectrum of the optical
afterglow contains several narrow metal lines which are consistent with the
burst occurring at a redshift of 2.140 +/- 0.001. The optical afterglow decays
as a power law with a slope of alpha = 0.83 +/- 0.04 for the first
approximately two days after the burst at which time there is evidence for a
break. The slope after the break is at least 1.4. There is evidence for rapid
variations in the R-band light approximately 0.5 days after the burst. These
variations suggest that there are density fluctuations near the gamma-ray burst
on spatial scales of approximately 40--125 AU. The magnitude of the break in
the light curve, the spectral slope, and the rate of decay in the optical,
suggest that the burst expanded into an ambient medium that is homogeneous on
large scales. We estimate that the local particle density is between
approximately 0.1 and 10 cm^{-3} and that the total gamma-ray energy in the
burst was 1.2--1.9 x 10^{50} erg. This energy is smaller than, but consistent
with, the ``standard'' value of (5 +/- 2) x 10^{50} erg. Comparing the observed
color of the optical afterglow with predictions of the standard beaming model
suggests that the rest-frame V-band extinction in the host galaxy is less than
approximately 0.03 mag.Comment: 17 pages, 4 figures, AASTeX 5.02, to appear in AJ Referee's report
incorporated, minor changes in the tex
GRB 070714B - Discovery of the Highest Spectroscopically Confirmed Short Burst Redshift
Gemini Nod & Shuffle spectroscopy on the host of the short GRB 070714B shows
a single emission line at 7167 angstroms which, based on a grizJHK photometric
redshift, we conclude is the 3727 angstrom [O II] line. This places the host at
a redshift of z=.923 exceeding the previous record for the highest
spectroscopically confirmed short burst redshift of z=.546 held by GRB 051221.
This dramatically moves back the time at which we know short bursts were being
formed, and suggests that the present evidence for an old progenitor population
may be observationally biased.Comment: Conference procedings for Gamma Ray Bursts 2007 November 5-9, 2007
Santa Fe, New Mexico (4 pages, 2 figures
Infrared and Optical Observations of GRB 030115 and its Extremely Red Host Galaxy: Implications for Dark Bursts
We present near-infrared (nIR) and optical observations of the afterglow of
GRB 030115. Discovered in an infrared search at Kitt Peak 5 hours after the
burst trigger, this afterglow is amongst the faintest observed in the R-band at
an early epoch, and exhibits very red colors, with . The
magnitude of the optical afterglow of GRB 030115 is fainter than many upper
limits for other bursts, suggesting that without early nIR observations it
would have been classified as a ``dark'' burst. Both the color and optical
magnitude of the afterglow are likely due to dust extinction and indicate that
at least some optical afterglows are very faint due to dust along the line of
sight. Multicolor {\it Hubble Space Telescope} observations were also taken of
the host galaxy and the surrounding field. Photometric redshifts imply that the
host, and a substantial number of faint galaxies in the field are at . The overdensity of galaxies is sufficiently great that GRB 030115 may
have occurred in a rich high-redshift cluster. The host galaxy shows extremely
red colors (R-K=5) and is the first GRB host to be classified as an Extremely
Red Object (ERO). Some of the galaxies surrounding the host also show very red
colors, while the majority of the cluster are much bluer, indicating ongoing
unobscured star formation. As it is thought that much of high redshift star
formation occurs in highly obscured environments it may be that GRB 030115
represent a transition object, between the relatively unobscured afterglows
seen to date and a population which are very heavily extinguished, even in the
nIR.Comment: 19 Pages. ApJ 2006, 647, 47
Real-Time Detection and Rapid Multiwavelength Follow-up Observations of a Highly Subluminous Type II-P Supernova from the Palomar Transient Factory Survey
The Palomar Transient Factory (PTF) is an optical wide-field variability
survey carried out using a camera with a 7.8 square degree field of view
mounted on the 48-in Oschin Schmidt telescope at Palomar Observatory. One of
the key goals of this survey is to conduct high-cadence monitoring of the sky
in order to detect optical transient sources shortly after they occur. Here, we
describe the real-time capabilities of the PTF and our related rapid
multiwavelength follow-up programs, extending from the radio to the gamma-ray
bands. We present as a case study observations of the optical transient
PTF10vdl (SN 2010id), revealed to be a very young core-collapse (Type II-P)
supernova having a remarkably low luminosity. Our results demonstrate that the
PTF now provides for optical transients the real-time discovery and
rapid-response follow-up capabilities previously reserved only for high-energy
transients like gamma-ray bursts.Comment: ApJ, in press; all spectroscopic data available from the Weizmann
Institute of Science Experimental Astrophysics Spectroscopy System (WISEASS;
http://www.weizmann.ac.il/astrophysics/wiseass/
Rapid UBVRI Follow-up of the Highly Collimated Optical Afterglow of GRB010222
(Abridged) We present the earliest optical observations of the optical
counterpart to the GRB 010222, obtained with the FLWO 1.2-m telescope in UBVRI
passbands, starting 3.64 hours after the burst. We also present late R-band
observations of the afterglow obtained with the 1.8-m VATT ~25 days after the
burst. The temporal analysis of our data joined with published data indicates a
steepening decay, independent of wavelength, asymptotically approaching
t^{-0.80+/-0.05} at early times (t << 1 day) and t^{-1.30+/-0.05} at late
times, with a sharp break at t_b=0.72+/-0.1 days. This is the second earliest
observed break of any afterglow (after GRB 980519), which clearly indicates the
importance of rapid multi-band follow-up for GRB afterglow research. The
optical spectral energy distribution, corrected for small Galactic reddening,
can be fit fairly well by a single power-law with a slope of -1.07+/-0.09.
However, when we fit using our BVRI data only, we obtain a shallower slope of
-0.88+/- 0.1, in excellent agreement with the slope derived from our
low-resolution spectrum (-0.89 +/- 0.03). The spectral slope and light curve
decay slopes we derive are not consistent with a jet model despite the presence
of a temporal break. Significant host dust extinction with a star-burst
reddening law would flatten the spectral index to match jet predictions and
still be consistent with the observed spectral energy distribution. We derive
an opening angle of 2.1 deg, smaller than any listed in the recent compilation
of Frail et al. The total beamed energy corrected for the jet geometry is
4x10^50 erg, very close to the ``standard'' value of 5x10^50 erg found by Frail
et al. for a number of other bursts with light-curve breaks.Comment: revised version (minor changes only) to be published in the ApJ Part
1, 12 pages, 4 figures; all data used for the fits and our CCD frames
available at ftp://cfa-ftp.harvard.edu/pub/kstanek/GRB010222/ and through WWW
at http://cfa-www.harvard.edu/cfa/oir/Research/GRB
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