Central Bureau for Astronomical Telegrams
IAUC 6096: EXO 1846-031; 1994r
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Circular No. 6096
Central Bureau for Astronomical Telegrams
INTERNATIONAL ASTRONOMICAL UNION
Postal Address: Central Bureau for Astronomical Telegrams
Smithsonian Astrophysical Observatory, Cambridge, MA 02138, U.S.A.
IAUSUBS@CFA.HARVARD.EDU or FAX 617-495-7231 (subscriptions)
Phone 617-495-7244/7440/7444 TWX 710-320-6842 ASTROGRAM CAM
MARSDEN@CFA.HARVARD.EDU or GREEN@CFA.HARVARD.EDU (science)
EXO 1846-031
S. N. Zhang, B. A. Harmon, C. A. Wilson, G. J. Fishman, and W.
S. Paciesas, Marshall Space Flight Center, NASA; J. E. Grindlay and
D. Barret, Harvard-Smithsonian Center for Astrophysics (CfA); and
E. Ford, M. Tavani, and P. Kaaret, Columbia University, report: "A
recent outburst from the x-ray transient EXO 1846-031 has been
detected by BATSE. An earth-occultation image, integrated between
Sept. 21 and 30, showed a significant peak consistent with the
location of EXO 1846-031. The location uncertainty is 0o.1 perpendicular
to a line between the source location (R.A. = 18h49m.3, Decl.
= -3o04', equinox 2000.0) and R.A. = 18h56m, Decl. = +6o.0, and
extends about +/-1o along the line centered on the source. No
other catalogued hard x-ray sources are consistent with the bright
peak. Although the statistical accuracy is poor, the outburst
began around Sept. 15 +/- 3 and peaked on Sept. 23 +/- 3. As of
Oct. 8 +/- 3 days, the source has dropped below the sensitivity
limit of BATSE. This source is a black-hole candidate because of
its ultrasoft spectral component and hard x-ray tail. Between
Sept. 21 and Oct. 1, the spectrum could be acceptably fitted by a
power law at least to 100 keV with an index of -2.9 +/- 0.2. The
average flux (band 20-100 keV) during this interval was about 80
+/- 20 mCrab. We note that the original EXOSAT observations
(Parmar et al. 1993, A.Ap. 279, 179) showed a decay constant for
soft x-rays of 85 days. The BATSE power law is consistent with
the 1985 EXOSAT observation of a hard tail above 10 keV.
Immediate follow-up observations at optical (the counterpart has
not been identified yet), radio, and soft x-ray wavelengths are
strongly encouraged."
J. Grindlay, M. Garcia, and P. Zhao, CfA, report: "B. McLean
obtained moderately deep I-band imaging of the EXOSAT error circle
for EXO 1846-031 (Parmar et al., ibid.) with the 1.2-m telescope at
the Whipple Observatory on Oct. 14.15 UT. No optical counterpart
brighter than I = 21.5 in the EXOSAT error circle was detected,
suggesting that the source is either very distant or heavily
absorbed or that this outburst decayed more quickly. Deeper
observations would still be useful."
COMET MACHHOLZ (1994r)
Total visual magnitude estimate by C. S. Morris, Pine Mountain
Club, CA (0.26-m reflector): Oct. 12.47 UT, 10.6 (5' coma).
1994 October 15 (6096) Daniel W. E. Green
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