87 research outputs found
Helios-2 Vela-Ariel-5 gamma-ray burst source position
The gamma-ray burst of 28 January 1976, one of 18 events thus far detected in interplanetary space with Helios-2, was also observed with the Vela-5A, -6A and the Ariel-5 satellites. A small source field is obtained from the intersection of the region derived from the observed time delays between Helios-2 and Vela-5A and -6A with the source region independently found with the Ariel-5 X-ray detector. This area contains neither any steady X-ray source as scanned by HEAO-A nor any previously catalogued X-ray, radio or infrared sources, X-ray transients, quasars, seyferts, globular clusters, flare stars, pulsars, white dwarfs or high energy gamma-ray sources. The region is however, within the source field of a gamma-ray transient observed in 1974, which exhibited nuclear gamma-ray line structure
Relativity at Action or Gamma-Ray Bursts
Gamma ray Bursts (GRBs) - short bursts of few hundred keV -rays -
have fascinated astronomers since their accidental discovery in the sixties.
GRBs were ignored by most relativists who did not expect that they are
associated with any relativistic phenomenon. The recent observations of the
BATSE detector on the Compton GRO satellite have revolutionized our ideas on
these bursts and the picture that emerges shows that GRBs are the most
relativistic objects discovered so far.Comment: 7 pages, 4th prize in this years gravity essay competition to appear
in General Relativity and Gravitation. Complete PS file is available at
ftp://shemesh.fiz.huji.ac.il or at
http://shemesh.fiz.huji.ac.il/papers/essay96.u
Observation of GRB 030131 with the INTEGRAL satellite
A long Gamma-Ray Burst (GRB) was detected with the instruments on board the
INTEGRAL satellite on January 31 2003. Although most of the GRB, which lasted
150 seconds, occurred during a satellite slew, the automatic software of
the INTEGRAL Burst Alert System was able to detect it in near-real time. Here
we report the results obtained with the IBIS instrument, which detected GRB
030131 in the 15 keV - 200 keV energy range, and ESO/VLT observations of its
optical transient. The burst displays a complex time profile with numerous
peaks. The peak spectrum can be described by a single power law with photon
index 1.7 and has a flux of 2 photons cm s in
the 20-200 keV energy band. The high sensitivity of IBIS has made it possible
for the first time to perform detailed time-resolved spectroscopy of a GRB with
a fluence of 7 erg cm (20-200 keV).Comment: Accepted for publication in A&A, 5 pages, 4 figures, late
Gamma-Ray Bursts via the Neutrino Emission from Heated Neutron Stars
A model is proposed for gamma-ray bursts based upon a neutrino burst of about
10^52 ergs lasting a few seconds above a heated collapsing neutron star. This
type of thermal neutrino burst is suggested by relativistic hydrodynamic
studies of the compression, heating, and collapse of close binary neutron stars
as they approach their last stable orbit, but may arise from other sources as
well. We present a hydrodynamic simulation of the formation and evolution of
the pair plasma associated with such a neutrino burst. This pair plasma leads
to the production of ~10^51 - 10^52 ergs in gamma-rays with spectral and
temporal properties consistent with observed gamma-ray bursts.Comment: Final version. 30 pages, 10 figures, 6 tables, accepted for
publication in The Astrophysical Journa
Distribution of compact object mergers around galaxies
Compact object mergers are one of the currently favored models for the origin
of GRBs. The discovery of optical afterglows and identification of the nearest,
presumably host, galaxies allows the analysis of the distribution of burst
sites with respect to these galaxies. Using a model of stellar binary evolution
we synthesize a population of compact binary systems which merge within the
Hubble time. We include the kicks in the supernovae explosions and calculate
orbits of these binaries in galactic gravitational potentials. We present the
resulting distribution of merger sites and discuss the results in the framework
of the observed GRB afterglows.Comment: 8 pages, 5 figures, submitted to MNRA
The Wolf-Rayet features and mass-metallicity relation of long-duration gamma-ray burst host galaxies
Aims. We have gathered optical spectra of 8 long-duration GRB host galaxies
selected from the archival data of VLT/FORS2. We investigated whether or not
Wolf-Rayet (WR) stars can be detected in these GRB host galaxies. We also tried
to estimate the physical properties of GRB host galaxies, such as metallicity.
Methods. We identified the WR features in these spectra by fitting the WR
bumps and WR emission lines in blue and red bumps. We also identified the
subtypes of the WR stars, and estimated the numbers of stars in each subtype,
then calculated the WR/O star ratios. The (O/H) abundances of GRB hosts were
estimated from both the electron temperature (Te) and the metallicity-sensitive
strong-line ratio (R23), for which we have broken the R23 degeneracy. We
compared the environments of long-duration GRB host galaxies with those of
other galaxies in terms of their luminosity (stellar mass)-metallicity
relations (LZ, MZ).
Results. We detected the presence of WR stars in 5 GRB host galaxies having
spectra with relatively high signal-to-noise ratios (S/N). In the comparison of
LZ, MZ relations, it shows that GRB hosts have lower metallicities than other
samples with comparable luminosity and stellar mass. The presence of WR stars
and the observed high WR/O star ratio, together with low metallicity, support
the core-collapsar model and implie the first stage of star formation in the
hosted regions of GRBs.Comment: 12 pages, 4 figures, A&A 514, A24 (2010
Physics, Astrophysics and Cosmology with Gravitational Waves
Gravitational wave detectors are already operating at interesting sensitivity
levels, and they have an upgrade path that should result in secure detections
by 2014. We review the physics of gravitational waves, how they interact with
detectors (bars and interferometers), and how these detectors operate. We study
the most likely sources of gravitational waves and review the data analysis
methods that are used to extract their signals from detector noise. Then we
consider the consequences of gravitational wave detections and observations for
physics, astrophysics, and cosmology.Comment: 137 pages, 16 figures, Published version
<http://www.livingreviews.org/lrr-2009-2
Gravitational-wave research as an emerging field in the Max Planck Society. The long roots of GEO600 and of the Albert Einstein Institute
On the occasion of the 50th anniversary since the beginning of the search for
gravitational waves at the Max Planck Society, and in coincidence with the 25th
anniversary of the foundation of the Albert Einstein Institute, we explore the
interplay between the renaissance of general relativity and the advent of
relativistic astrophysics following the German early involvement in
gravitational-wave research, to the point when gravitational-wave detection
became established by the appearance of full-scale detectors and international
collaborations. On the background of the spectacular astrophysical discoveries
of the 1960s and the growing role of relativistic astrophysics, Ludwig Biermann
and his collaborators at the Max Planck Institute for Astrophysics in Munich
became deeply involved in research related to such new horizons. At the end of
the 1960s, Joseph Weber's announcements claiming detection of gravitational
waves sparked the decisive entry of this group into the field, in parallel with
the appointment of the renowned relativist Juergen Ehlers. The Munich area
group of Max Planck institutes provided the fertile ground for acquiring a
leading position in the 1970s, facilitating the experimental transition from
resonant bars towards laser interferometry and its innovation at increasingly
large scales, eventually moving to a dedicated site in Hannover in the early
1990s. The Hannover group emphasized perfecting experimental systems at pilot
scales, and never developed a full-sized detector, rather joining the LIGO
Scientific Collaboration at the end of the century. In parallel, the Max Planck
Institute for Gravitational Physics (Albert Einstein Institute) had been
founded in Potsdam, and both sites, in Hannover and Potsdam, became a unified
entity in the early 2000s and were central contributors to the first detection
of gravitational waves in 2015.Comment: 94 pages. Enlarged version including new results from further
archival research. A previous version appears as a chapter in the volume The
Renaissance of General Relativity in Context, edited by A. Blum, R. Lalli and
J. Renn (Boston: Birkhauser, 2020
Discovery of the Near-IR Afterglow and of the Host of GRB 030528
The rapid dissemination of an arcmin-sized HETE-2 localization of the
long-duration X-ray flash GRB 030528 led to a ground-based multi-observatory
follow-up campaign. We report the discovery of the near-IR afterglow, and also
describe the detection of the underlying host galaxy in the optical and near-IR
bands. The afterglow is classified as "optically dark" as it was not detected
in the optical band. The K-band photometry presented here suggests that the
lack of optical detection was simply the result of observational limitations
(lack of rapid and deep observations plus high foreground extinction). Simple
power law fits to the afterglow in the K-band suggest a typically decay with a
slope of alpha=1.2. The properties of the host are consistent with the idea
that GRB hosts are star forming blue galaxies. The redshift of GRB 030528 can
not be determined accurately, but the data favour redshifts less than unity. In
addition, we present an optical and near-IR analysis of the X-ray source CXOU
J170354.0--223654 from the vicinity of GRB 030528.Comment: 12 pages, 9 figures, A&A accepte
Fermi/GBM observations of the ultra-long GRB 091024: A burst with an optical flash
In this paper we examine gamma-ray and optical data of GRB 091024, a
gamma-ray burst (GRB) with an extremely long duration of T90~1020 s, as
observed with the Fermi Gamma-Ray Burst Monitor (GBM). We present spectral
analysis of all three distinct emission episodes using data from Fermi/GBM.
Because of the long nature of this event, many ground-based optical telescopes
slewed to its location within a few minutes and thus were able to observe the
GRB during its active period. We compare the optical and gamma-ray light
curves. Furthermore, we estimate a lower limit on the bulk Lorentz factor from
the variability and spectrum of the GBM light curve and compare it with that
obtained from the peak time of the forward shock of the optical afterglow. From
the spectral analysis we note that, despite its unusually long duration, this
burst is similar to other long GRBs, i.e. there is spectral evolution (both the
peak energy and the spectral index vary with time) and spectral lags are
measured. We find that the optical light curve is highly anti-correlated to the
prompt gamma-ray emission, with the optical emission reaching the maximum
during an epoch of quiescence in the prompt emission. We interpret this
behavior as the reverse shock (optical flash), expected in the
internal-external shock model of GRB emission but observed only in a handful of
GRBs so far. The lower limit on the initial Lorentz factor deduced from the
variability time scale ()is consistent within
the error to the one obtained using the peak time of the forward shock
() and is also consistent with Lorentz factors of other long
GRBs.Comment: accepted for publication in A&
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