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IAUC 7715: XTE J1650-500

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                                                  Circular No. 7715
Central Bureau for Astronomical Telegrams
Mailstop 18, Smithsonian Astrophysical Observatory, Cambridge, MA 02138, U.S.A.
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XTE J1650-500
     M. Revnivtsev and R. Sunyaev, Max-Planck-Institut fuer
Astrophysik and Russian Space Research Institute, write:  "Analysis
of public-domain data of the target-of-opportunity RXTE
observations of XTE J1650-500 (cf. IAUC 7707, 7708, 7710) from
Sept. 9 and 10 reveals the presence of two quasiperiodic-
oscillation (QPO) peaks (likely harmonics).  The centroid-peak
frequencies changed from 1.13 +/- 0.02 and 2.28 +/- 0.02 Hz on
Sept. 9.1 UT to 1.33 +/- 0.02 and 2.73 +/- 0.03 Hz on Sept. 10.5.
The amplitudes of the QPOs are about 5-7 percent.  The preliminary
spectral analysis of PCA (3-20 keV) and HEXTE (20-200 keV) data
shows that the source has a spectrum similar to that of Cyg X-1 and
other black-hole binaries in the low/hard spectral state.  The
spectrum has a power-law-like shape with photon index around
1.5-1.8 and exponential cutoff with e-folding value about 90 keV.
The investigation of reported QPOs in the optical band could
provide additional information about properties of the accretion
disk and the binary."
     R. Wijnands, J. M. Miller, and W. H. G. Lewin, Massachusetts
Institute of Technology, report on behalf of a larger
collaboration:  "A timing analysis of the RXTE PCA data obtained
for the new x-ray transient XTE J1650-500 on four occasions on
Sept. 6.98 (0.37 Crab), 7.13 (0.39 Crab), 8.38 (0.44 Crab), and
9.11 UT (0.45 Crab) demonstrates that the rapid x-ray variability
of this source can be characterized by a strong (about 22 percent
rms amplitude in the energy band 2-60 keV), band-limited noise
component, which follows a power law with index of 1-1.5 at high
frequencies with a break at 0.2 Hz, below which the spectrum is
relatively flat.  Superimposed on this noise component, broad
(width of 0.5-1.5 Hz) features or QPOs are present with a frequency
of 1.6-2.3 Hz.  Also a broad (width of 0.4 Hz) feature at half the
QPO frequency is detected.  An example of the power-density
spectrum of the source can be found at
http://space.mit.edu/~rudy/XTEJ1650-500PDS.ps (obtained for the
observation on Sept. 9.11).  The spectral shape (IAUC 7707) and the
timing behavior indicate that this is a black-hole binary in the
low (spectrally hard) state."
     M. M. Buxton, Research School of Astronomy and Astrophysics,
Australian National University; and D. Londish, University of
Sydney, report that the optical counterpart of XTE J1650-500 was
visible at B = 18.21 +/- 0.2 on Sept. 10.42 UT on two 300-s CCD
exposures taken with the 1.88-m telescope (+ Monash Cassegrain
Imager) at Mount Stromlo Observatory.

                      (C) Copyright 2001 CBAT
2001 September 11              (7715)            Daniel W. E. Green

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