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Circular No. 6050
Central Bureau for Astronomical Telegrams
INTERNATIONAL ASTRONOMICAL UNION
Postal Address: Central Bureau for Astronomical Telegrams
Smithsonian Astrophysical Observatory, Cambridge, MA 02138, U.S.A.
Telephone 617-495-7244/7440/7444 (for emergency use only)
TWX 710-320-6842 ASTROGRAM CAM EASYLINK 62794505
MARSDEN@CFA or GREEN@CFA (.SPAN, .BITNET or .HARVARD.EDU)
X-RAY NOVA IN SCORPIUS
T. Belloni, Astronomical Institute 'Anton Pannekoek', University
of Amsterdam, writes: "We have analyzed the ROSAT archive data
for the source 1ES 1649-403 (IAUC 6048), which has been proposed as
a counterpart of the BATSE x-ray nova in Scorpius (IAUC 6046). The
ROSAT PSPC observation was made over an 18-day period in 1991 Feb./
Mar.; the source is clearly detected at a large off-axis angle,
which, however, does not affect the results of our analysis. The
source shows strong variability; at the beginning (Feb. 28) and at
the end (Mar. 18) of the observations, it is at a constant level of
about 0.1 count/s (total 0.1- to 2.4-keV flux about 10E12 erg cmE-2
sE-1), while in the middle of the observation its count rate is
increasing over a period of 12 000 s, reaching an apparent peak of
0.9 count/s on Mar. 3. The x-ray spectrum shows a considerable
number of counts below 0.4 keV, indicative of a negligible
interstellar absorption. A fit to a thermal spectrum gives NH < 3 x
10E19 cmE-2 and kT > 1 keV. The absence of a substantial absorption
suggests that the source is located nearby, and the observed time
variability indicates that it might be a flare star. We therefore
conclude that this source cannot be a counterpart for the recently-
discovered BATSE x-ray nova."
C. Bailyn, S. Jogee, and J. Orosz, Department of Astronomy,
Yale University, report: "CCD imaging of the field of GRO J1655-40
(IAUC 6046) with the Cerro Tololo 0.9-m telescope (+ 2048 Tek CCD)
has revealed a candidate optical counterpart for the high-energy
nova. The optical nova is located at R.A. = 16h54m00s, Decl. =
-39o50'44" (equinox 2000.0; +/- 2"); its magnitude and colors on
Aug. 11.038 UT were V = 14.2, B-V = +1.1, V-R = +0.8, R-I = +0.7
(+/- 0.1 mag). The digitized U.K. Schmidt Sky Survey shows only an
object of V about 18 at this location. This object may be a near
neighbor of the nova that is visible on the CCD images (and not
associated with the quiescent nova). The red color of the nova
suggests that, if it is associated with GRO J1655-40, it is
significantly absorbed. The candidate also shows an excess of 0.45 mag
in a 7.5-nm-wide filter centered on H-alpha, relative to other
stars in the field. We have also imaged the field of 1ES 1649-403
(IAUC 6048) and find no sources significantly brighter than they
appear on the sky survey. Cerro Tololo currently has no spectroscopic
instruments available, so spectroscopic confirmation from
other observatories is urgently requested. Finding charts may be
obtained from orosz@astro.yale.edu
."
1994 August 11 (6050) Daniel W. E. Green
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