Central Bureau for Astronomical Telegrams
IAUC 6055: X-RAY N IN Sco; 1994o
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Circular No. 6055
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
R. M. Hjellming, National Radio Astronomy Observatory, reports:
"Very Large Array radio observations of the field of GRO J1655-40
on Aug. 12.18 UT at frequencies of 1.4, 4.9, and 14.9 GHz show the
presence of a very strong radio source located at R.A. = 16h54m00s.20,
Decl. = -39o50'43".6 (equinox 2000.0; +/- 0".5), with flux densities
of 1.04, 1.13, and 0.76 Jy, respectively (+/- 5 percent). This
radio source was unresolved (</= 0".5), and -- with a location only
3" from the position of the optical counterpart reported by Bailyn
et al. (IAUC 6050, with a position uncertainty of 2") -- is
coincident with both that optical counterpart and the variable radio
source observed by Campbell-Wilson and Hunstead (IAUC 6052). The
Molonglo Synthesis Telescope observations at 843 MHz, showed flux
densities of 0.37, 0.77, and 0.9 Jy on Aug. 6.60, 11.59, and 12.33,
respectively -- so the rising radio counterpart of the x-ray nova
had a non-thermal synchrotron radio spectrum on Aug. 12 with a peak
near 5 GHz. This is the strongest optically-thick radio emission
ever seen for a soft x-ray transient, and the strongest seen in any
state two weeks after outburst. It may be similar to the long-
lived, optically-thick radio source associated with the transient
GS 2023+338 (V404 Cyg; Han and Hjellming 1992, Ap.J. 400, 304)."
D. Campbell-Wilson and R. Hunstead, University of Sydney,
report the results of further radio observations of the field of
GRO J1655-40, using the Molonglo Observatory Synthesis Telescope at
843 MHz: "Following our previous report (IAUC 6052), the radio
emission has increased spectacularly, reaching 4.2 Jy (+/- 5
percent) at Aug. 14.58 UT and 5.5 Jy (+/- 5 percent) at Aug. 15.19.
If we assume an exponential increase from Aug. 11 to 15, the implied
time constant is 1.8 days. However, the overall rate of increase
from Aug. 6 to 15 appears to be faster than exponential, even
allowing for a possible quiescent level. Observations at other
frequencies are essential for monitoring the spectrum of the emission
and its evolution with time."
COMET MACHHOLZ (1994o)
H. Mikuz, Ljubljana, Slovenia, reports that a CCD image with a
0.20-m f/2 Baker-Schmidt camera yields V = 11.0 on Aug. 15.97 UT.
A 1-min exposure on Aug. 16.009 shows a prominent, slightly curved
jet of gas extending about 3' out of the comet nucleus in p.a. 350o.
1994 August 16 (6055) Daniel W. E. Green
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