641 research outputs found
The GRB Variability/Peak Luminosity Correlation: new results
We report test results of the correlation between time variability and peak
luminosity of Gamma-Ray Bursts (GRBs), using a larger sample (32) of GRBs with
known redshift than that available to Reichart et al. (2001), and using as
variability measure that introduced by these authors. The results are puzzling.
Assuming an isotropic-equivalent peak luminosity, as done by Reichart et al.
(2001), a correlation is still found, but it is less relevant, and inconsistent
with a power law as previously reported. Assuming as peak luminosity that
corrected for GRB beaming for a subset of 16 GRBs with known beaming angle, the
correlation becomes little less significant.Comment: 11 pages, 10 figures, MNRAS, accepte
Atomic Hydrogen Properties of AGN Host Galaxies: HI in 16 NUclei of GAlaxies (NUGA) Sources
We present a comprehensive spectroscopic imaging survey of the distribution
and kinematics of atomic hydrogen (HI) in 16 nearby spiral galaxies hosting low
luminosity AGN, observed with high spectral and spatial resolution (resolution:
~20 arcsec, 5 km/s) using the NRAO Very Large Array (VLA). The sample contains
a range of nuclear types, ranging from Seyfert to star-forming nuclei and was
originally selected for the NUclei of GAlaxies project (NUGA) - a spectrally
and spatially resolved interferometric survey of gas dynamics in nearby
galaxies designed to identify the fueling mechanisms of AGN and the relation to
host galaxy evolution. Here we investigate the relationship between the HI
properties of these galaxies, their environment, their stellar distribution and
their AGN type. The large-scale HI morphology of each galaxy is classified as
ringed, spiral, or centrally concentrated; comparison of the resulting
morphological classification with AGN type reveals that ring structures are
significantly more common in LINER than in Seyfert host galaxies, suggesting a
time evolution of the AGN activity together with the redistribution of the
neutral gas. Dynamically disturbed HI disks are also more prevalent in LINER
host galaxies than in Seyfert host galaxies. While several galaxies are
surrounded by companions (some with associated HI emission), there is no
correlation between the presence of companions and the AGN type
(Seyfert/LINER).Comment: 54 pages, 7 figures, accepted for publication in AJ. The
full-resolution version is available at
http://www.mpia.de/homes/haan/research.htm
The slope of the GRB Variability/Peak Luminosity Correlation
From a sample of 32 GRBs with known redshift (Guidorzi et al. 2005) and then
a sample of 551 BATSE GRBs with derived pseudo-redshift (Guidorzi 2005), the
time variability/peak luminosity correlation (V vs. L) found by Reichart et al.
(2001) was tested. For both samples the correlation is still found but less
relevant due to a much higher spread of the data. Assuming a straight line in
the logL-logV plane (logL = m logV + b), as done by Reichart et al., the slope
was found lower than that derived by Reichart et al.: m = 1.3_{-0.4}^{+0.8}
(Guidorzi et al. 2005), m = 0.85 +- 0.02 (Guidorzi 2005), to be compared with m
= 3.3^{+1.1}_{-0.9} (Reichart et al. 2001). Reichart & Nysewander (2005)
attribute the different slope to the fact we do not take into account in the
fit the variance of the sample, and demonstrate that, using the method by
Reichart (2001), the data set of Guidorzi et al. (2005) in logL-logV plane is
still well described with slope m = 3.4^{+0.9}_{-0.6}. Here we compare the
results of two methods accounting for the variance of the sample, that
implemented by Reichart (2001) and that by D'Agostini (2005). We demonstrate
that the method by Reichart (2001) provides an inconsistent estimate of the
slope when the sample variance is comparable with the interval of values
covered by the variability. We also show that, using the D'Agostini method, the
slope is consistent with that derived by us earlier and inconsistent with that
derived by Reichart & Nysewander (2005). Finally we discuss the implications on
the interpretations and show that our results are in agreement with the peak
energy/variability correlation found by Lloyd-Ronning & Ramirez-Ruiz (2002) and
the peak energy/peak luminosity correlation (Yonetoku et al. 2004; Ghirlanda et
al. 2005) [abridged].Comment: 9 pages, 10 figures, accepted by MNRA
Early GRB Optical and Infrared Afterglow Observations with the 2-m Robotic Liverpool Telescope
We present the first optical observations of a Gamma Ray Burst (GRB)
afterglow using the 2-m robotic Liverpool Telescope (LT), which is owned and
operated by Liverpool John Moores University and situated on La Palma. We
briefly discuss the capabilities of LT and its suitability for rapid follow-up
observations of early optical and infrared GRB light curves. In particular, the
combination of aperture, site, instrumentation and rapid response (robotic
over-ride mode aided by telescope's rapid slew and fully-opening enclosure)
makes the LT ideal for investigating the nature of short bursts, optically-dark
bursts, and GRB blast-wave physics in general. We briefly describe the LT's key
position in the RoboNet-1.0 network of robotic telescopes. We present the LT
observations of GRB041006 and use its gamma-ray properties to predict the time
of the break in optical light curve, a prediction consistent with the
observations.Comment: 4 pages, 1 figure, accepted for publication in Il nuovo cimento (4th
Workshop Gamma-Ray Bursts in the Afterglow Era, Rome, 18-22 October 2004
Rapid GRB Follow-up with the 2-m Robotic Liverpool Telescope
We present the capabilities of the 2-m robotic Liverpool Telescope (LT),
owned and operated by Liverpool John Moores University and situated at ORM, La
Palma. Robotic control and scheduling of the LT make it especially powerful for
observations in time domain astrophysics including: (i) rapid response to
Targets of Opportunity: Gamma Ray Bursts, novae, supernovae, comets; (ii)
monitoring of variable objects on timescales from seconds to years, and (iii)
observations simultaneous or coordinated with other facilities, both
ground-based and from space. Following a GRB alert from the Gamma Ray
Observatories HETE-2, INTEGRAL and Swift we implement a special over-ride mode
which enables observations to commence in about a minute after the alert,
including optical and near infrared imaging and spectroscopy. In particular,
the combination of aperture, site, instrumentation and rapid response (aided by
its rapid slew and fully-opening enclosure) makes the LT excellently suited to
help solving the mystery of the origin of optically dark GRBs, for the
investigation of short bursts (which currently do not have any confirmed
optical counterparts) and for early optical spectroscopy of the GRB phenomenon
in general. We briefly describe the LT's key position in the RoboNet-1.0
network of robotic telescopes.Comment: 6 pages, 2 figures, to appear in the proceedings of Interacting
Binaries: Accretion, Evolution and Outcomes, 4-10 July 2004, Cefalu, Sicily,
Italy, eds. Antonelli et a
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