94 research outputs found
GRB 970228 Revisited: Evidence for a Supernova in the Light Curve and La te Spectral Energy Distribution of the Afterglow
At the time of its discovery, the optical and X-ray afterglow of GRB 970228
appeared to be a ringing endorsement of the previously untried relativistic
fireball model of gamma-ray burst (GRB) afterglows, but now that nearly a dozen
optical afterglows to GRBs have been observed, the wavering light curve and
reddening spectrum of this afterglow make it perhaps the most difficult of the
observed afterglows to reconcile with the fireball model. In this Letter, we
argue that this afterglow's unusual temporal and spectral properties can be
attributed to a supernova that overtook the light curve nearly two weeks after
the GRB. This is the strongest case yet for a GRB/supernova connection. It
strengthens the case that a supernova also dominated the late afterglow of GRB
980326, and the case that GRB 980425 is related to SN 1998bw.Comment: Accepted to The Astrophysical Journal (Letters), 14 pages, LaTe
No Radio Afterglow from the Gamma-Ray Burst of February 28, 1997
We present radio observations of the gamma-ray burster GRB 970228 made with
the Very Large Array (VLA) and the Owens Valley Radio Observatory (OVRO)
spanning a range of postburst timescales from one to 300 days. A search for a
time-variable radio source was conducted covering an area which included a
fading X-ray source and an optical transient, both of which are thought to be
the long wavelength counterparts to the gamma-ray burst. At the position of the
optical transient sensitive limits between 10 uJy and 1 mJy can be placed on
the absence of a radio counterpart to GRB 970228 between 1.4 and 240 GHz. We
apply a simple formulation of a fireball model which has been used with some
success to reproduce the behavior of the optical and X-ray light curves. Using
this model we conclude that the radio non-detections are consistent with the
peak flux density of the afterglow lying between 20-40 uJy and it requires that
the optical flux peaked between 4 and 16 hours after the burst.Comment: ApJ Let (submitted
Numerical Models of Binary Neutron Star System Mergers. I.: Numerical Methods and Equilibrium Data for Newtonian Models
The numerical modeling of binary neutron star mergers has become a subject of
much interest in recent years. While a full and accurate model of this
phenomenon would require the evolution of the equations of relativistic
hydrodynamics along with the Einstein field equations, a qualitative study of
the early stages on inspiral can be accomplished by either Newtonian or
post-Newtonian models, which are more tractable. In this paper we offer a
comparison of results from both rotating and non-rotating (inertial) frame
Newtonian calculations. We find that the rotating frame calculations offer
significantly improved accuracy as compared with the inertial frame models.
Furthermore, we show that inertial frame models exhibit significant and
erroneous angular momentum loss during the simulations that leads to an
unphysical inspiral of the two neutron stars. We also examine the dependence of
the models on initial conditions by considering initial configurations that
consist of spherical neutron stars as well as stars that are in equilibrium and
which are tidally distorted. We compare our models those of Rasio & Shapiro
(1992,1994a) and New & Tohline (1997). Finally, we investigate the use of the
isolated star approximation for the construction of initial data.Comment: 32 pages, 19 gif figures, manuscript with postscript figures
available at http://www.astro.sunysb.edu/dswesty/docs/nspap1.p
The Extinction Towards the GRB970228 Field
We determine the local galactic extinction towards the field of gamma-ray
burst GRB970228 using a variety of methods. We develop a maximum likelihood
method for measuring the extinction by comparing galaxy counts in the field of
interest to those in a field of known extinction, and apply this method to the
GRB970228 field. We also measure the extinction by comparing the observed
stellar spectral energy distributions of stars in the GRB970228 field to the
spectral energy distribution of library spectra of the same spectral type.
Finally we estimate the extinction using the Balmer emission line ratios of a
galaxy in the GRB970228 field, and the neutral hydrogen column density and
amount of infrared dust emission toward this field. Combining the results of
these methods, we find a best-fit galactic extinction in the optical of
, which implies a a substantial dimming and change of
the spectral slope of the intrinsic GRB970228 afterglow.Comment: 22 pages, including 7 figures. Submitted to Ap
A Photometric Investigation of the GRB970228 Afterglow and the Associated Nebulosity
We carefully analyze the WFPC2 and STIS images of GRB970228. We measure
magnitudes for the GRB970228 point source component in the WFPC2 images of
, and
, on March 26 and April 7,
respectively; and on September 4 in the STIS image.
For the extended component, we measure magnitudes of
in the combined WFPC2 images and
in the STIS image, which are consistent with no
variation. This value is fainter than previously reported (Galama et al. 98)
and modifies the previously assumed magnitudes for the optical transient when
it faded to a level where the extended source component contribution was not
negligible, alleviating the discrepancy to a power-law temporal behavior. We
also measure a color of for the
extended source component. Taking into account the extinction measured in this
field (Castander & Lamb 1998), this color implies that the extended source is
most likely a galaxy with ongoing star formation.Comment: 21 pages, including 8 figures. Submitted to Ap
High Contrast Imaging in the Visible: First Experimental Results at the Large Binocular Telescope
In February 2014, the SHARK-VIS (System for High contrast And coronography
from R to K at VISual bands) Forerunner, a high contrast experimental imager
operating at visible wavelengths, was installed at LBT (Large Binocular
Telescope). Here we report on the first results obtained by recent on-sky
tests. These results show the extremely good performance of the LBT ExAO
(Extreme Adaptive Optics) system at visible wavelengths, both in terms of
spatial resolution and contrast achieved. Similarly to what was done by (Amara
et al. 2012), we used the SHARK-VIS Forerunner data to quantitatively assess
the contrast enhancement. This is done by injecting several different synthetic
faint objects in the acquired data and applying the ADI (angular differential
imaging) technique. A contrast of the order of is obtained
at 630 nm for angular separations from the star larger than 100 mas. These
results are discussed in light of the future development of SHARK-VIS and
compared to those obtained by other high contrast imagers operating at similar
wavelengths.Comment: Astronomical Journal - Accepted for publicatio
Discovery of the heavily obscured supernova 2002cv
On the 13th of May 2002, supernova 2002cv was discovered using a
near-infrared camera working at the AZT-24 1.1m telescope at Campo Imperatore
(AQ-Italy). After the infrared detection a simultaneous photometric follow-up
was started at optical wavelengths. The preliminary results confirm a heavily
obscured object with a V-K color not lower than 6 magnitudes, making SN 2002cv
the most reddened supernova ever observed. This finding, along with the recent
discovery of another obscured supernova, suggests a critical revision of the
rates known to date. The estimate of the visual extinction and the light curves
are provided here. These latter indicate that our SN 2002cv observations are
the earliest available for a type-Ia supernova at IR wavelengths.Comment: 4 page
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