816 research outputs found
Gamma Ray Bursts in the Era of Rapid Followup
We present a status report on the study of gamma-ray bursts (GRB) in the era
of rapid follow-up using the world's largest robotic optical telescopes - the
2-m Liverpool and Faulkes telescopes. Within the context of key unsolved issues
in GRB physics, we describe (1) our innovative software that allows real-time
automatic analysis and interpretation of GRB light curves, (2) the novel
instrumentation that allows unique types of observations (in particular, early
time polarisation measurements) and (3) the key science questions and
discoveries to which robotic observations are ideally suited, concluding with a
summary of current understanding of GRB physics provided by combining rapid
optical observations with simultaneous observations at other wavelengths.Comment: 20 pages, 12 figures; Review article accepted for publication in
Advances in Astronomy, special issue 'Robotic Astronomy (Hindawi Publishing
Corporation)
Gas Dynamics in the Barred Seyfert Galaxy NGC4151 - II. High Resolution HI Study
We present sensitive, high angular resolution (6" x 5") 21-cm observations of
the neutral hydrogen in the nearby barred Seyfert galaxy, NGC4151. These HI
observations, obtained using the VLA in B-configuration, are the highest
resolution to date of this galaxy, and reveal hitherto unprecedented detail in
the distribution and kinematics of the HI on sub-kiloparsec scales. A complete
analysis and discussion of the HI data are presented and the global properties
of the galaxy are related to the bar dynamics presented in Paper I.Comment: 13 pages including 9 figures and 3 tables; accepted for publication
in MNRA
Gigahertz-Peaked Spectrum Radio Sources in Nearby Galaxies
There is now strong evidence that many low-luminosity AGNs (LLAGNs) contain
accreting massive black holes and that the nuclear radio emission is dominated
by parsec-scale jets launched by these black holes. Here, we present
preliminary results on the 1.4 GHz to 667 GHz spectral shape of a well-defined
sample of 16 LLAGNs. The LLAGNs have a falling spectrum at high GHz
frequencies. Several also show a low-frequency turnover with a peak in the 1-20
GHz range. The results provide further support for jet dominance of the core
radio emission. The LLAGNs show intriguing similarities with gigahertz-peaked
spectrum (GPS) sources.Comment: 6 pages, to appear in ASP Conference series, 2002, Vol. 25
Nuclear gas dynamics in Arp 220 - sub-kiloparsec scale atomic hydrogen disks
We present new, high angular resolution (~0.22") MERLIN observations of
neutral hydrogen (HI) absorption and 21-cm radio continuum emission across the
central ~900 parsecs of the ultraluminous infrared galaxy, Arp220. Spatially
resolved HI absorption is detected against the morphologically complex and
extended 21-cm radio continuum emission, consistent with two counterrotating
disks of neutral hydrogen, with a small bridge of gas connecting the two.
We propose a merger model in which the two nuclei represent the galaxy cores
which have survived the initial encounter and are now in the final stages of
merging, similar to conclusions drawn from previous CO studies (Sakamoto,
Scoville & Yun 1999). However, we suggest that instead of being coplanar with
the main CO disk (in which the eastern nucleus is embedded), the western
nucleus lies above it and, as suggested by bridge of HI connecting the two
nuclei, will soon complete its final merger with the main disk. We suggest that
the collection of radio supernovae (RSN) detected in VLBA studies in the more
compact western nucleus represent the second burst of star formation associated
with this final merger stage and that free-free absorption due to ionised gas
in the bulge-like component can account for the observed RSN distribution.
(Abridged)Comment: 26 pages including 8 figures and 1 table; accepted for publication in
Ap
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