342 research outputs found
Annihilation radiation in cosmic gamma-ray bursts
The pair annihilation radiation in gamma-ray bursts is seen as broad lines with extended hard wings. This radiation is suggested to escape in a collimated beam from magnetic polar regions of neutron stars
3rd Interplanetary Network Localization, Time History, Fluence, Peak Flux, and Distance Lower Limit of the February 28, 1997 Gamma-Ray Burst
The gamma-ray burst of 1997 February 28 was localized using the arrival-time
analysis method with the Ulysses, BeppoSAX, and WIND spacecraft. The result is
a plus-or-minus 31.5 arcsec (3 sigma) wide annulus of possible arrival
directions which intersects both the position of the burst determined
independently by the SAX Wide Field Camera, and the position of a fading X-ray
source detected by the SAX focussing X-ray telescopes, and reduces these source
location areas by factors of 7 and 1.5 respectively. The combination of the
annulus and the SAX locations, a 0.76 square arcminute error box, is consistent
with that of an optical transient source and an extended object, possibly a
galaxy. We also present the time history, peak flux, and fluence of this event,
and derive a model-independent lower limit to the source distance of ~11000 AU.Comment: 11 pages, postscript, 2 figures. Accepted for publication in ApJ
Letter
Interplanetary Network Localization of GRB991208 and the Discovery of its Afterglow
The extremely energetic (~10^-4 erg/cm^2) gamma-ray burst (GRB) of 1999
December 8 was triangulated to a ~14 sq. arcmin. error box ~1.8 d after its
arrival at Earth with the 3rd interplanetary network (IPN), consisting of the
Ulysses, Near Earth Asteroid Rendezvous (NEAR), and WIND spacecraft. Radio
observations with the Very Large Array ~2.7 d after the burst revealed a bright
fading counterpart whose position is consistent with that of an optical
transient source whose redshift is z=0.707. We present the time history, peak
flux, fluence, and refined 1.3 sq. arcmin. error box of this event, and discuss
its energetics. This is the first time that a counterpart has been found for a
GRB localized only by the IPN.Comment: Revised version, accepted for publication in the Astrophysical
Journal Letter
Tricritical Phenomena at the Cerium Transition
The isostructural transition in the
CeLaTh system is measured as a function of La alloying
using specific heat, magnetic susceptibility, resistivity, thermal
expansivity/striction measurements. A line of discontinuous transitions, as
indicated by the change in volume, decreases exponentially from 118 K to close
to zero with increasing La doping and the transition changes from being
first-order to continuous at a critical concentration . At the tricritical point, the coefficient of the linear term in the
specific heat and the magnetic susceptibility start to increase
rapidly near = 0.14 and gradually approaches large values at =0.35
signifying that a heavy Fermi-liquid state evolves at large doping. Near ,
the Wilson ratio, , has a value of 3.0, signifying the presence of
magnetic fluctuations. Also, the low-temperature resistivity shows that the
character of the low-temperature Fermi-liquid is changing
The second Konus-Wind catalog of short gamma-ray bursts
In this catalog, we present the results of a systematic study of 295 short
gamma-ray bursts (GRBs) detected by Konus-Wind (KW) from 1994 to 2010. From the
temporal and spectral analyses of the sample, we provide the burst durations,
the spectral lags, the results of spectral fits with three model functions, the
total energy fluences and the peak energy fluxes of the bursts. We discuss
evidence found for an additional power-law spectral component and the presence
of extended emission in a fraction of the KW short GRBs. Finally, we consider
the results obtained in the context of the Type I (merger-origin) / Type II
(collapsar-origin) classifications.Comment: Accepted to the Astrophysical Journal Supplement Series (7 Figures, 8
Tables
Observations of a possible new soft gamma repeater, SGR1801-23
We report on two observations of a soft bursting source in 1997 June, whose
time histories and energy spectra are consistent with those of the soft gamma
repeaters. The source can only be localized to an ~3.8 degree long error box in
the direction of the Galactic center, whose area is ~ 80 sq. arcmin. The
location of the source, while not consistent with that of any of the four known
soft repeaters, is consistent with those of several known and possible
supernova remnants.Comment: 13 pages, 3 figures. Submitted to Ap. J. Letter
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