75 research outputs found
SkyDOT (Sky Database for Objects in the Time Domain): A Virtual Observatory for Variability Studies at LANL
The mining of Virtual Observatories (VOs) is becoming a powerful new method
for discovery in astronomy. Here we report on the development of SkyDOT (Sky
Database for Objects in the Time domain), a new Virtual Observatory, which is
dedicated to the study of sky variability. The site will confederate a number
of massive variability surveys and enable exploration of the time domain in
astronomy. We discuss the architecture of the database and the functionality of
the user interface. An important aspect of SkyDOT is that it is continuously
updated in near real time so that users can access new observations in a timely
manner. The site will also utilize high level machine learning tools that will
allow sophisticated mining of the archive. Another key feature is the real time
data stream provided by RAPTOR (RAPid Telescopes for Optical Response), a new
sky monitoring experiment under construction at Los Alamos National Laboratory
(LANL).Comment: to appear in SPIE proceedings vol. 4846, 11 pages, 5 figure
Real-Time Detection of Optical Transients with RAPTOR
Fast variability of optical objects is an interesting though poorly explored
subject in modern astronomy. Real-time data processing and identification of
transient celestial events in the images is very important for such study as it
allows rapid follow-up with more sensitive instruments. We discuss an approach
which we have developed for the RAPTOR project, a pioneering closed-loop system
combining real-time transient detection with rapid follow-up. RAPTOR's data
processing pipeline is able to identify and localize an optical transient
within seconds after the observation. The testing we performed so far have been
confirming the effectiveness of our method for the optical transient detection.
The software pipeline we have developed for RAPTOR can easily be applied to the
data from other experiments.Comment: 10 pages, 7 figures, to appear in SPIE proceedings vol. 484
The RAPTOR Experiment: A System for Monitoring the Optical Sky in Real Time
The Rapid Telescopes for Optical Response (RAPTOR) experiment is a spatially
distributed system of autonomous robotic telescopes that is designed to monitor
the sky for optical transients. The core of the system is composed of two
telescope arrays, separated by 38 kilometers, that stereoscopically view the
same 1500 square-degree field with a wide-field imaging array and a central 4
square-degree field with a more sensitive narrow-field "fovea" imager. Coupled
to each telescope array is a real-time data analysis pipeline that is designed
to identify interesting transients on timescales of seconds and, when a
celestial transient is identified, to command the rapidly slewing robotic
mounts to point the narrow-field ``fovea'' imagers at the transient. The two
narrow-field telescopes then image the transient with higher spatial resolution
and at a faster cadence to gather light curve information. Each "fovea" camera
also images the transient through a different filter to provide color
information. This stereoscopic monitoring array is supplemented by a rapidly
slewing telescope with a low resolution spectrograph for follow-up observations
of transients and a sky patrol telescope that nightly monitors about 10,000
square-degrees for variations, with timescales of a day or longer, to a depth
about 100 times fainter. In addition to searching for fast transients, we will
use the data stream from RAPTOR as a real-time sentinel for recognizing
important variations in known sources. Altogether, the RAPTOR project aims to
construct a new type of system for discovery in optical astronomy--one that
explores the time domain by "mining the sky in real time".Comment: 11 pages, To appear in the Proceedings of the SPIE, Volume 484
Observations of the Optical Counterpart to XTE J1118+480 During Outburst by the ROTSE-I Telescope
The X-ray nova XTE J1118+480 exhibited two outbursts in the early part of
2000. As detected by the Rossi X-ray Timing Explorer (RXTE), the first outburst
began in early January and the second began in early March. Routine imaging of
the northern sky by the Robotic Optical Transient Search Experiment (ROTSE)
shows the optical counterpart to XTE J1118+480 during both outbursts. These
data include over 60 epochs from January to June 2000. A search of the ROTSE
data archives reveal no previous optical outbursts of this source in selected
data between April 1998 and January 2000. While the X-ray to optical flux ratio
of XTE J1118+480 was low during both outbursts, we suggest that they were full
X-ray novae and not mini-outbursts based on comparison with similar sources.
The ROTSE measurements taken during the March 2000 outburst also indicate a
rapid rise in the optical flux that preceded the X-ray emission measured by the
RXTE by approximately 10 days. Using these results, we estimate a pre-outburst
accretion disk inner truncation radius of 1.2 x 10^4 Schwarzschild radii.Comment: 9 pages, 1 table, 2 figure
Fast X-ray Transients and Their Connection to Gamma-Ray Bursts
Fast X-ray transients (FXTs) with timescales from seconds to hours have been
seen by numerous space instruments. We have assembled archival data from
Ariel-5, HEAO-1 (A-1 and A-2), WATCH, ROSAT, and Einstein to produce a global
fluence-frequency relationship for these events. Fitting the log N-log S
distribution over several orders of magnitude to simple power law we find a
slope of -1.0. The sources of FXTs are undoubtedly heterogeneous, the -1 power
law is an approximate result of the summation of these multiple sources. Two
major contributions come from gamma-ray bursts and stellar flares.
Extrapolating from the BATSE catalog of GRBs, we find that the fraction of
X-ray flashes that can be the X-ray counterparts of gamma-ray bursts is a
function of fluence. Certainly most FXTs are not counterparts of standard
gamma-ray bursts. The fraction of FXTs from non-GRB sources, such as magnetic
stars, is greatest for the faintest FXTs. Our understanding of the FXT
phenomenon remains limited and would greatly benefit from a large, homogeneous
data set, which requires a wide-field, sensitive instrument.Comment: 36 pages, 8 figure
The central region of M31 observed with XMM-Newton (I. Group properties and diffuse emission)
We present the results of a study based on an XMM-Newton Performance
Verification observation of the central 30 arcmin of the nearby spiral galaxy
M31. In the 34-ks European Photon Imaging Camera (EPIC) exposure, we detect 116
sources down to a limiting luminosity of 6 x 10^35 erg/s (0.3--12 keV, d = 760
kpc). The luminosity distribution of the sources detected with XMM-Newton
flattens at luminosities below ~ 2.5 x 10^37 erg/s. We make use of hardness
ratios for the detected sources in order to distinguish between classes of
objects such as super-soft sources and intrinsically hard or highly absorbed
sources. We demonstrate that the spectrum of the unresolved emission in the
bulge of M31 contains a soft excess which can be fitted with a ~ 0.35-keV
optically-thin thermal-plasma component clearly distinct from the composite
point-source spectrum. We suggest that this may represent diffuse gas in the
centre of M31, and we illustrate its extent in a wavelet-deconvolved image.Comment: to appear in the XMM-Newton special issue of A&A (Vol 365, January
2001). High-resolution versions of fig. 1 and fig. 6 available on reques
The second ROSAT PSPC survey of M31 and the complete ROSAT PSPC source list
This paper reports the results of the analysis of the second ROSAT PSPC
survey of M31 performed in summer 1992. We compare our results with those of
the first survey. Within the ~10.7 deg^2 field of view, 396 individual X-ray
sources are detected in the second survey data, of which 164 are new
detections. When combined with the first survey, this result in a total of 560
X-ray sources in the field of M31. Their (0.1 keV - 2.0 keV) fluxes range from
7 x 10^-15 to 7.6 x 10^-12 erg cm^-2 s^-1, and of these 560 sources, 55 are
tentatively identified with foreground stars, 33 with globular clusters, 16
with supernova remnants, and 10 with radio sources and galaxies (including
M32). A comparison with the results of the Einstein M31 survey reveals 491
newly detected sources, 11 long term variable sources, and 7 possible transient
sources. Comparing the two ROSAT surveys, we come up with 34 long term variable
sources and 8 transient candidates. For the M31 sources, the observed
luminosities range from 4 x 10^35 to 4 x 10^38 erg s^-1. The total (0.1 keV -
2.0 keV) luminosity of M31 is (3.4+-0.3) x 10^39 erg s^-1, distributed
approximately equally between the bulge and disk. Within the bulge region, the
luminosity of a possible diffuse component combined with faint sources below
the detection threshold is (2.0+-0.5) x 10^38 erg s^-1. An explanation in terms
of hot gaseous emission leads to a maximum total gas mass of (1.0+-0.3) x 10^6
M_sun.Comment: 39 pages, 3 figures (figure 2 on page 5 should be printed in color).
Accepted (03.04.2001) for publication in A&
Novel mutations in the TBX5 gene in patients with Holt-Oram Syndrome
The Holt-Oram syndrome (HOS) is an autosomal dominant condition characterized by upper limb and cardiac malformations. Mutations in the TBX5 gene cause HOS and have also been associated with isolated heart and arm defects. Interactions between the TBX5, GATA4 and NKX2.5 proteins have been reported in humans. We screened the TBX5, GATA4, and NKX2.5 genes for mutations, by direct sequencing, in 32 unrelated patients presenting classical (8) or atypical HOS (1), isolated congenital heart defects (16) or isolated upper-limb malformations (7). Pathogenic mutations in the TBX5 gene were found in four HOS patients, including two new mutations (c.374delG; c.678G > T) in typical patients, and the hotspot mutation c.835C > T in two patients, one of them with an atypical HOS phenotype involving lower-limb malformations. Two new mutations in the GATA4 gene were found in association with isolated upper-limb malformations, but their clinical significance remains to be established. A previously described possibly pathogenic mutation in the NKX2.5 gene (c.73C > 7) was detected in a patient with isolated heart malformations and also in his clinically normal father
Astronomy & Astrophysics The central region of M 31 observed with XMM-Newton I. Group properties and diffuse emission
Abstract. We present the results of a study based on an XMM-Newton Performance Verification observation of the central 30 of the nearby spiral galaxy M 31. In the 34-ks European Photon Imaging Camera (EPIC) exposure, we detect 116 sources down to a limiting luminosity of 6 10 35 erg s â1 (0.3-12 keV, d = 760 kpc). The luminosity distribution of the sources detected with XMM-Newton flattens at luminosities below âŒ2.5 10 37 erg s â1 . We make use of hardness ratios for the detected sources in order to distinguish between classes of objects such as super-soft sources and intrinsically hard or highly absorbed sources. We demonstrate that the spectrum of the unresolved emission in the bulge of M 31 contains a soft excess which can be fitted with a âŒ0.35-keV optically-thin thermal-plasma component clearly distinct from the composite point-source spectrum. We suggest that this may represent diffuse gas in the centre of M 31, and we illustrate its extent in a wavelet-deconvolved image
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