Robotic Optical Transient Search Experiment
ROTSE observations of the X-ray Transient XTE
On March 30th, R. Remillard, et al. reported
the observation of a new X-ray source, XTE J1118+480, detected by the RXTE All-Sky Monitor
(IAU Circular 7389). With retrospective data analysis, they found this object to have
slowly risen in intensity since March 5th with earlier flares recorded in January.
Analysis of sky patrol images obtained by the ROTSE-I camera array shows that this object
varys significantly at optical wavelengths as well. Images obtained at 54 epochs from
January 4, 2000 through March 28, 2000 have now been analyzed, showing a strong
correlation of optical intensity with the x-ray fluxes observed by RXTE. The
resulting light curve is shown in the figure below. This retrospective analysis is
being carried farther backward in time as we retrieve images from our two-year archival
Click here to see graph in
A search of USNO-scanned Palomar plates shows no evidence for this object
at eight different epochs spanning 1950 to 1997.
A ROTSE-I image of XTE J1118+480 shows the
transient in roughly the center of the frame with a small circle drawn around the expected
location. That image can be compared with a Palomar
image taken in 1953. The bright star in the Palomar print corresponds to the bright
star just slightly left of center in the ROTSE-I image.
These recent ROTSE results have been distributed as IAU Circular 7394 //cfa-www.harvard.edu/iauc/RecentIAUCs.html.
Our search for gamma ray burst optical counterparts in six of our
ROTSE-I triggered bursts was accepted by ApJ Letters (astro-ph/0001438). No optical
counterparts were observed, implying that optical and gamma ray emission are not strongly
correlated. A preliminary version of these results was submitted to the Space Telescope
Science Institute's 1999 May Symposium (astro-ph/9909219), and this paper is useful as a
hardware and operations reference for the experiment.
We also have submitted a paper on
SGR's at the Huntsville GRB Symposium last fall. These results are being finalized for
Our first ROTSE-I catalog of regular and long period variables has been accepted for
publication in AJ April, 2000 (astro-ph/0001388). Approximately 5% of the sky was
studied down to magnitude 15.5 revealing about 1600 new variables, including many new RR
In collaboration with J. Zinn et al., our 1998 Leonids results were published in
Meteoritics and Planetary Science 34, 1007-1015 (1999).
The ROTSE Project:
ROTSE is an experimental program to search for astrophysical optical transients on time
scales of a fraction of a second to a few hours. This is an area of astronomical science
that has been relatively unexplored until now. The primary incentive for this research is
to find the optical counterparts of gamma-ray bursts (GRBs). These mysterious events are
manifested by brief (~10 seconds) intense flashes of gamma-rays with typical photon
energies of the order of 1 MeV.
The ROTSE project is designed and operated by a collaboration of astrophysicists from
the Los Alamos National Laboratory, Lawrence Livermore National Laboratory and the University of Michigan. Since March 1998, we have
logged over 1.2 Terabytes of sky images which are being studied for a variety of
The ROTSE research program is supported by NASA,
NSF, the Research
Corporation, The Planetary Society and the
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Last updated: February 8, 2001.
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