209 research outputs found
The unusual host galaxy of the BL Lac object PKS 1413+135
The BL Lacertae object PKS 1413+135 is associated with a disk dominated
galaxy which heavily absorbs the BL Lac nucleus at optical and X-ray
wavelengths. It has been argued whether this galaxy is actually the host galaxy
of PKS 1413+135 or whether the BL Lac is a background QSO, gravitationally
lensed by the apparent host galaxy. We have obtained deep high resolution
H-band images of this unusual BL Lac object using the UKIRT IRCAM3. Our
observations show that the BL Lac nucleus is centered within < 0.05 arcsec of
the galaxy. Based on this result we assess the probability for the lensing
scenario and come to the conclusion that the disk galaxy is indeed the host of
PKS 1413+135. The galaxy shows peanut-shaped isophotes, suggesting the presence
of a central bar which is a common feature of AGNComment: accepted for publication in MNRAS, 5 pages with 2 Postscript figure
Cross-correlation of the unresolved X-ray background with faint galaxies
At the faint end of the deepest X-ray surveys, a population of X-ray luminous
galaxies is seen. In this paper, we present the results of a cross-correlation
between the residual, unresolved X-ray photons in a very deep X-ray survey and
the positions of faint galaxies, in order to examine the importance of these
objects at even fainter flux levels. We measure a significant correlation on
all angular scales up to ~1 arcmin. This signal could account for a significant
fraction of the unresolved X-ray background, approximately 35 per cent if the
clustering is similar to optically selected galaxies. However, the angular form
of the correlation is seen to be qualitatively similar to that expected for
clusters of galaxies and the X-ray emission could be associated with hot gas in
clusters or with QSOs within galaxy clusters rather than emission from
individual faint galaxies. The relative contribution from each of these
possibilities cannot be determined with the current data.Comment: 7 pages LaTeX including 9 EPS figures. Uses mn.sty. Accepted for
publication by MNRA
The discovery of very red counterparts to faint X-ray sources
We present deep K-band imaging at the positions of four very faint X-ray
sources found in the UK ROSAT Deep Survey to have no optical counterpart
brighter than R~23. Likely identifications are found within the ROSAT error
circle in all four fields with R-K colours of between 3.2 +/- 0.4 and 6.4 +/-
0.6. From a consideration of the R-K colours and X-ray to optical luminosity
ratios of the candidate identifications, we tentatively classify two of the
X-ray sources as very distant (z ~ 1) clusters of galaxies, one as a narrow
emission line galaxy and one as an obscured QSO.Comment: 7 pages, LaTeX, 7 figures (1 postscript file each). Uses mn.sty and
epsf.sty. Accepted by MNRAS. For more information see
http://www.astro.soton.ac.uk/~amn/UKdee
Microlensing of Extended Stellar Sources
We investigate the feasibility of reconstructing the radial intensity profile
of extended stellar sources by inverting their microlensed light curves. Using
a simple, linear, limb darkening law as an illustration, we show that the
intensity profile can be accurately determined, at least over the outer part of
the stellar disc, with realistic light curve sampling and photometric errors.
The principal requirement is that the impact parameter of the lens be less than
or equal to the stellar radius. Thus, the analysis of microlensing events
provides a powerful method for testing stellar atmosphere models.Comment: 4 pages LaTeX, to appear in New Astronomy Reviews - proceedings of
the Oxford Workshop `Gravitational Lensing: Nature's Own Weighing Scales'.
Uses elsart.cls. Paper also available at
ftp://info.astro.gla.ac.uk/pub/martin/extended.p
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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