Bibcode
Grindlay, J.; Barret, D.; Bloser, P.; Garcia, M.; McClintock, J.; Zhao, P.; Zhang, S.; Harmon, A.; Paciesas, W.; Ford, E.; Kaaret, P.; Tavani, M.
Bibliographical reference
American Astronomical Society, 185th AAS Meeting, #116.07; Bulletin of the American Astronomical Society, Vol. 26, p.1514
Advertised on:
12
1994
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Description
Black hole candidates (BHCs) are increasingly found as luminous hard
x-ray sources, with spectra exending up to 100-200 keV, which undergo
transient outbursts and appear as "X-ray novae" for durations of
typically 10-100 days. The BATSE detectors on CGRO constitute a powerful
all-sky monitor and have detected the brightest of these, with peak
fluxes typically 1-3 times that of the Crab, at a rate of 1-2/year.
Optical counterparts of these suggest they are typically within 3-5 kpc.
The CfA-BATSE team has initiated a survey for much fainter BHCs in an
effort to better constrain the total population of BH binaries in the
Galaxy. Our search will extend down to transients with peak outbursts of
about 0.1 Crab, which should then occur at a total rate of about 10/year
in the Galaxy. We are studying 7 historical BHC transients to both
search for recurrent outbursts as well as new (faint) transients in
their adjoining fields. In the field for the BHC and ultra-soft source
EXO1846-031 (cf. Parmar et al 1993, Astron. Ap., 279, 179), we have
found in collaboration with the Columbia team a recurrent outburst in
September 1992. Further analysis has revealed three other outbursts,
with recurrence times of typically 300-400 days, outburst durations of
about 10-30 days, and peak fluxes of about 0.1 Crab. The most recent
outburst (beginning about September 23, 1994, and discovered on October
13) was searched for an optical counterpart with moderately deep I-band
imaging with the 1.2m telescope at the Whipple Observatory on UT 14.15
October. No optical counterpart brighter than I = 21.5 in the EXOSAT
error circle (Parmar et al) was detected, suggesting the source is
either very distant or heavily absorbed or that this outburst decayed
more quickly. Results will be presented for both the x-ray data,
including spectra, and the optical search for this still unidentified
BHC. A general progress report for the Faint Black Hole Transient Survey
will also be provided.