Central Bureau for Astronomical Telegrams
IAUC 4608: RADIO OUTBURST IN Cyg X IN 1985
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Circular No. 4608
Central Bureau for Astronomical Telegrams
INTERNATIONAL ASTRONOMICAL UNION
Postal Address: Central Bureau for Astronomical Telegrams
Smithsonian Astrophysical Observatory, Cambridge, MA 02138, U.S.A.
TWX 710-320-6842 ASTROGRAM CAM Telephone 617-495-7244/7440/7444
MARSDEN or GREEN@CFA.BITNET MARSDEN or GREEN@CFAPS2.SPAN
RADIO OUTBURST IN CYGNUS X IN 1985
L. A. Higgs and T. L. Landecker, Dominion Radio Astrophysical
Observatory; and H. J. Wendker, Hamburg Observatory, communicate:
"Comparison of two separate 408-MHz radio maps of the Cygnus X region,
made using the DRAO (Penticton) aperture-synthesis radio telescope,
has revealed the existence of a strong radio outburst in 1985. The
radio source probably reached a peak flux density in excess of 40 Jy
within a day or two of 1985 Sept. 23. The position of the outburst,
R.A. = 20h41m10s.4 +/- 1s.7, Decl. = +40D17'13" +/- 30" (equinox
1950.0), does not correspond with any previously known variable radio
source. The Cygnus X region was first observed with the DRAO
telescope by us in Aug. 1985 and, averaged over the 35 days required
for a synthesis observation, only a weak radio source (about 140 mJy
at 408 MHz) was noted at the position of the subsequent burst. In the
following month, a nearby, partially overlapping field was observed at
408 MHz (by F. Israel and J. Bally), and the data were made available
to DRAO. A detailed comparison of the observed flux densities of
point sources in the two observations brought the radio outburst to
our attention. The average flux density of the outburst in the Sept.
1985 observations was 35 +/- 10 Jy. (The large error estimate results
from the fact that the source appeared at a position where the
primary-beam response of the synthesis telescope was very low--between
1 and 3 percent--and hence rather uncertain.) A detailed analysis of
the aperture-synthesis data acquired in Sept. 1985 indicates that the
radio source increased in flux during the 35-day observation, reaching
a peak probably in excess of 40 Jy on Sept. 23, and thereafter it
declined. Observations made with the Effelsberg telescope in 1974 at
6 cm show the presence of an extended radio source near the position
of the radio outburst. Its flux density at 4.8 GHz is estimated to be
about 140 mJy. Recent VLA observations (May 1988) of the region of
the outburst also show the presence of a 4' diameter extended source
but with a weak embedded compact object (about 0.2 mJy at 4.8 GHz),
40" south of the outburst position. Other than this possible
association, there is no firm indication of the existence of a compact
radio source at the burst position before or after the Sept. 1985
event. The 408 MHz flux observed from this event is greater by about
a factor of ten than the 408-MHz burst observed from Cyg X-3 in 1972,
so a search of unpublished radio data from this region of Cygnus that
may exist would be well warranted."
1988 June 7 (4608) Brian G. Marsden
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