Central Bureau for Astronomical Telegrams
IAUC 6078: X-RAY N IN Sco
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Circular No. 6078
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
J. Greiner, Max Planck Institute for Extraterrestrial Physics,
reports: "The x-ray transient GRO J1655-40 was observed with the
ROSAT HRI for a total of 785 s, starting at Aug. 28.6616 UT. The
best-fit x-ray position is determined to be R.A. = 16h53m59s.9,
Decl. = -39o50'44" (equinox 2000.0), with a (mainly systematic)
error of +/- 8". This is only 2" off the radio (IAUC 6055) and
optical (IAUC 6060) positions. The mean x-ray flux is rather
constant at a HRI count rate of about 65 counts/s (corresponding to
roughly 300 mCrab in the range 0.1-2.4 keV) during the observation
interval, consistent with ASCA observations on Aug. 23 (IAUC 6063).
Superimposed on this mean level are x-ray flux variations between
20 and 150 counts/s on timescales down to 0.1 s. Previous ROSAT
PSPC observations did not show this source; the upper limits are
0.02 count/s (Aug. 1990, All-Sky-Survey) and 0.003 count/s (Sept.
1993, courtesy U. Herbstmeier). Adopting the absorption column
density of 5 x 10E21 cmE-2 and a power-law photon index of -2.1, as
determined with ASCA (IAUC 6063), the latter upper limit corresponds
to an unabsorbed flux of 2.7 x 10E-13 erg cmE-2 sE-1 in the range
0.1-2.4 keV -- a factor of 2.3 x 10**4 lower than the mean flux
during the HRI observation."
D. Campbell-Wilson, University of Sydney and Molonglo Observatory
Synthesis Telescope (MOST); D. J. McKay, Australia Telescope
National Facility; and J. E. Lovell, University of Tasmania, report
on continued flux-density monitoring of the radio source associated
with GRO J1655-40: "The source is undergoing a second major radio
outburst. Observations with the MOST and the AT Compact Array
revealed the presence of an optically-thick, flat-spectrum radio
source that appeared on Sept. 9 (see Hjellming and Rupen, IAUC 6077).
This new source had a radio spectrum that peaked at 0.45 Jy at 5
GHz on Sept. 11. On Sept. 14.32 UT, the source reached 1.6 Jy at
843 MHz, rising to 2.1 Jy on Sept. 14.45. Observations at Mt.
Pleasant Observatory at 2.3, 6.7, and 8.4 GHz show the spectrum of
the new outburst to be optically thin. This second outburst follows
the increased x-ray emission seen by the BATSE and GRANAT teams
(IAUC 6075, 6077). The second outburst suggests a binary origin for
GRO J1655-40, with a period of 31 +/- 1 days, based on the timing of
the previous radio flare (Campbell-Wilson and Hunstead, IAUC 6055)."
1994 September 15 (6078) Daniel W. E. Green
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