3,918 research outputs found
The host galaxy of GRB010222: The strongest damped Lyman-alpha system known
Analysis of the absorption lines in the afterglow spectrum of the gamma-ray
burst GRB010222 indicates that its host galaxy (at a redshift of z=1.476) is
the strongest damped Lyman-alpha (DLA) system known, having a very low
metallicity and modest dust content. This conclusion is based on the detection
of the red wing of Lyman-alpha plus a comparison of the equivalent widths of
ultraviolet Mg I, Mg II, and Fe II lines with those in other DLAs. The column
density of H I, deduced from a fit to the wing of Lyman-alpha, is (5 +/- 2)
10^22 cm^-2. The ratio of the column densities of Zn and Cr lines suggests that
the dust content in our line of sight through the galaxy is low. This could be
due to either dust destruction by the ultraviolet emission of the afterglow or
to an initial dust composition different to that of the diffuse interstellar
material, or a combination of both.Comment: Submitted to MNRAS 12 page
VLT observations of GRB 990510 and its environment
We present BVRI photometry and spectrophotometry of GRB990510 obtained with
the ESO VLT/Antu telescope during the late decline phase. Between days 8 and 29
after the burst, the afterglow faded from R=24.2 to ~26.4. The spectral flux
distribution and the light curve support the interpretation of the afterglow as
synchrotron emission from a jet. The light curve is consistent with the optical
transient alone but an underlying SN with maximum brightness R>27.4 or a galaxy
with R>27.6 (3-sigma upper limits) cannot be ruled out. To a 5-sigma detection
threshold of R=26.1, no galaxy is found within 6'' of the transient. A very
blue V~24.5 extended object which may qualify as a starburst galaxy is located
12'' SE, but at unknown redshift.Comment: 5 pages A&A Latex, accepted for publication in A&A Letter
The Supreme Court and the American Civil Liberties Union\u27s Colorblind Protection of Cross Burning in First Amendment Jurisprudence Legitimates White Supremacy
Not Availabl
SCUBA sub-millimeter observations of gamma-ray bursters. I. GRB 970508, 971214, 980326, 980329, 980519, 980703
We discuss the first results of our ongoing program of Target of Opportunity
observations of gamma-ray bursts (GRBs) using the SCUBA instrument on the James
Clerk Maxwell Telescope. We present the results for GRB 970508, 971214, 980326,
980329, 980519, and 980703.
Our most important result to date is the detection of a fading counterpart to
GRB 980329 at 850 microns. Although it proved to be difficult to find the
infrared counterpart to this burst, the sub-millimeter flux was relatively
bright. This indicates that intrinsically the brightness of this counterpart
was very similar to GRB 970508. The radio through sub-millimeter spectrum of
GRB 980329 is well fit by a power law with index alpha = +0.9. However, we
cannot exclude a nu^(1/3) power law attenuated by synchrotron self-absorption.
An alpha = +1 VLA-SCUBA power law spectrum is definitely ruled out for GRB
980703, and possibly also for GRB 980519.
We cannot rule out that part of the sub-millimeter flux from GRB 980329 comes
from a dusty star-forming galaxy at high redshift, such as the ones recently
discovered by SCUBA. Any quiescent dust contribution will be much larger at
sub-millimeter than at radio wavelengths. Both a high redshift and large dust
extinction would help explain the reddening of the counterpart to GRB 980329,
and a redshift of z = 5 has been suggested. The large intensity of this burst
might then indicate that beaming is important.Comment: 6 pages, 3 figures, submitted to Astronomy and Astrophysic
GRB990712: First Indication of Polarization Variability in a Gamma-ray Burst Afterglow
We report the detection of significant polarization in the optical afterglow
of GRB990712 on three instances 0.44, 0.70 and 1.45 days after the gamma-ray
burst, with (P, theta) being (2.9% +- 0.4%, 121.1 degr +- 3.5 degr), (1.2% +-
0.4%, 116.2 degr +- 10.1 degr) and (2.2% +- 0.7%, 139.2 degr +- 10.4 degr)
respectively. The polarization is intrinsic to the afterglow. The degree of
polarization is not constant, and smallest at the second measurement. The
polarization angle does not vary significantly during these observations. We
find that none of the existing models predict such polarization variations at
constant polarization angle, and suggest ways in which these models might be
modified to accommodate the observed behavior of this afterglow.Comment: 10 pages including 6 figures, accepted by ApJ. Uses aastex 5.
The discovery of polarization in the afterglow of GRB 990510 with the ESO Very Large Telescope
Following a BeppoSAX alert (Piro 1999a) and the discovery of the OT at SAAO
(Vreeswijk et al. 1999a), we observed GRB 990510 with the FORS instrument on
ESO's VLT Unit 1 (`Antu'). The burst is unremarkable in gamma rays, but in
optical is the first one to show good evidence for jet-like outflow (Stanek et
al. 1999, Harrison et al. 1999). We report the detection of significant linear
polarization in the afterglow: it is (1.6 +/- 0.2)% 0.86 days after trigger,
and after 1.81 days is consistent with that same value, but much more
uncertain. The polarization angle is constant on a time scale of hours, and may
be constant over one day. We conclude that the polarization is intrinsic to the
source and due to the synchrotron nature of the emission, and discuss the
random and ordered field geometries that may be responsible for it.Comment: submitted to ApJ Lett., 5 pages including 2 figures, uses
emulateapj.st
Evidence for a supernova in reanalyzed optical and near-infrared images of GRB970228
We present B-, V-, R_c-, I_c-, J-, H-, K- and K'-band observations of the
optical transient (OT) associated with GRB970228, based on a reanalysis of
previously used images and unpublished data. In order to minimize calibration
differences we have collected and analyzed most of the photometry and
consistently determined the magnitude of the OT relative to a set of secondary
field stars. We confirm our earlier finding that the early decay of the light
curves (before March 6, 1997) was faster than that at intermediate times
(between March 6 and April 7, 1997). At late times the light curves resume a
fast decay (after April 7, 1997). The early-time observations of GRB970228 are
consistent with relativistic blast-wave models but the intermediate- and
late-time observations are hard to understand in this framework. The
observations are well explained by an initial power law decay with index -1.73
+0.09 -0.12 modified at later times by a type-I_c supernova light curve.
Together with the evidence for GRB980326 and GRB980425 this gives further
support for the idea that at least some GRBs are associated with a possibly
rare type of supernova.Comment: Submitted to the Astrophysical Journal, 9 pages including 3 figures,
uses emulateapj.st
Spike-Train Responses of a Pair of Hodgkin-Huxley Neurons with Time-Delayed Couplings
Model calculations have been performed on the spike-train response of a pair
of Hodgkin-Huxley (HH) neurons coupled by recurrent excitatory-excitatory
couplings with time delay. The coupled, excitable HH neurons are assumed to
receive the two kinds of spike-train inputs: the transient input consisting of
impulses for the finite duration (: integer) and the sequential input
with the constant interspike interval (ISI). The distribution of the output ISI
shows a rich of variety depending on the coupling strength and the
time delay. The comparison is made between the dependence of the output ISI for
the transient inputs and that for the sequential inputs.Comment: 19 pages, 4 figure
Strategies for prompt searches for GRB afterglows: the discovery of the GRB 001011 optical/near-infrared counterpart using colour-colour selection
We report the discovery of the optical and near-infrared counterparts to GRB
001011. The GRB 001011 error box determined by Beppo-SAX was simultaneously
imaged in the near-infrared by the 3.58-m New Technology Telescope and in the
optical by the 1.54-m Danish Telescope ~8 hr after the gamma-ray event. Here we
implement the colour-colour discrimination technique proposed by Rhoads (2001)
and extend it using near-IR data as well. We present the results provided by an
automatic colour-colour discrimination pipe-line developed to discern the
different populations of objects present in the GRB 001011 error box. Our
software revealed three candidates based on single-epoch images. Second-epoch
observations carried out ~3.2 days after the burst revealed that the most
likely candidate had faded, thus identifying it with the counterpart to the
GRB. In deep R-band images obtained 7 months after the burst a faint
(R=25.38+/-0.25) elongated object, presumably the host galaxy of GRB 001011,
was detected at the position of the afterglow. The GRB 001011 afterglow is the
first discovered with the assistance of colour-colour diagram techniques. We
discuss the advantages of using this method and its application to error boxes
determined by future missions.Comment: Accepted for publication in Astronomy and Astrophysics, 13 pages, 16
figure
- …