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IAUC 7707: XTE J1650-500

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                                                  Circular No. 7707
Central Bureau for Astronomical Telegrams
INTERNATIONAL ASTRONOMICAL UNION
Mailstop 18, Smithsonian Astrophysical Observatory, Cambridge, MA 02138, U.S.A.
IAUSUBS@CFA.HARVARD.EDU or FAX 617-495-7231 (subscriptions)
CBAT@CFA.HARVARD.EDU (science)
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Phone 617-495-7440/7244/7444 (for emergency use only)


XTE J1650-500
     R. Remillard, reporting for the RXTE All-Sky Monitor (ASM)
team at the Massachusetts Institute of Technology and Goddard Space
Flight Center (GSFC), NASA, writes:  "The RXTE ASM has detected
x-ray emission from a new source, XTE J1650-500.  The ASM position
is centered at R.A. = 16h50m00s, Decl. = -50o00' (equinox 2000.0;
estimated uncertainty 6').  The first detection was made on Sept.
5.637 UT, with an x-ray intensity (2-12 keV) of 0.14(2) Crab,
rising to 0.24(1) Crab on Sept. 6.432 and 0.27(1) Crab on Sept.
6.896.  The ASM detections in the three energy bands suggest x-ray
colors consistent with a 'soft x-ray transient', rather than an
x-ray pulsar.  Observations at radio, optical, and infrared
wavelengths are needed as soon as possible."
     C. Markwardt, J. Swank, and E. Smith, GSFC, report on behalf
of the RXTE team at GSFC: "The transient x-ray source XTE J1650-500
discovered with the RXTE ASM was confirmed with PCA measurements on
Sept. 6.39 (0.33 Crab) and 6.62 UT (0.39 Crab).  PCA scans in the
second observation give a best fitting R.A. = 16h50m00s, Decl. =
-49o59' (equinox 2000.0; estimated uncertainty about 2').  The
continuum spectrum was a power law with a photon index of 1.5, plus
a blackbody with temperature kT = 1.2 keV (about 10 percent of
total), which is typical of hard states of black-hole candidates.
No pulsations were seen."
     A. J. Castro-Tirado, Instituto de Astrofisica de Andalucia,
Granada; P. Kilmartin, A. Gilmore, O. Petterson, and I. Bond, Mt.
John University Observatory; P. Yock, Auckland University; and C.
Sanchez-Fernandez, Laboratorio de Astrofisica Espacial y Fisica
Fundamental, Madrid, communicate:  "We have observed the RXTE error
box of the probable soft x-ray transient XTE J1650-500 with the Mt.
John Observatory 0.6-m telescope at Lake Tekapo, New Zealand.  A
180-s image obtained with a wide blue-band filter centered on the
RXTE position reveals a possible candidate of mag about 17
(preliminary) that might be present as a faint object (near the
detection limit) in the corresponding blue Palomar Sky Survey image.
A preliminary position is R.A. = 16h50m01s.0, Decl. = -49o57'45"
(equinox 2000.0; +/- 2"), which is nearly 1' south of the bright
star HDE 151476 (V = 8.0).  Spectroscopic observations are
encouraged in order to confirm whether this is the optical
counterpart to XTE J1650-500.  An identification chart is posted
at http://www.iaa.es/~ajct/XRBs/xtej1650.html."

                      (C) Copyright 2001 CBAT
2001 September 7               (7707)            Daniel W. E. Green

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