Central Bureau for Astronomical Telegrams
IAUC 5180: X-RAY OUTBURST near GRS 0831-429; A0538-66
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Circular No. 5180
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 or GREEN@CFA.BITNET MARSDEN or GREEN@CFAPS2.SPAN
X-RAY OUTBURST IN THE FIELD OF GRS 0831-429
R. Sunyaev, on behalf of the Granat team (Space Research Institute,
Moscow; and Danish Space Research Institute, Lyngby), reports:
"The All-Sky Monitor 'WATCH' detected a gradual increase of x-ray
flux from the source in the field of GRS 0831-429, with the following
fluxes measured in the 10- to 60-keV energy band: Jan. 17, 160
mCrab; Jan. 18, 180 mCrab; Jan. 21, 230 mCrab; Jan. 23, 270 mCrab;
and Jan. 25, 310 mCrab. A reconstructed position of the source is
consistent with the position reported on IAUC 5122, the uncertainty
being 1 deg. Observations carried out during the last ten days of
1990 December and the first half of 1991 January did not reveal any
source in that region brighter than 120 mCrab. Earlier observations
on 1990 Oct. 15, 16, 23, and 24 showed the x-ray flux from the GRS
0831-429 field at close to 400 mCrab. On Dec. 19, 22, and 23, the
main instruments aboard Granat observed this field. The ART-P
telescope detected two sources in the energy band 4-30 keV within its
field-of-view. Their positions (R.A. = 8h34m08s, Decl. = -43 00'.9;
and R.A. = 8h35m35s, Decl. = -42 42'.3, equinox 1950.0, accuracy 1'),
agree with the ROSAT data (IAUC 5142). The southern source is
inside the 90-percent confidence error circle of GRS 0831-429. The
northern source is 11' off MX 0836-42 but outside its 90-percent
error box. From the northern source we observed pulsations with a
heliocentric period 12.327396 +/- 0.000008 s (on Dec. 22). Pulsations
of x-ray flux with similar period from this general area were
reported previously by Ginga (IAUC 5139, 5148) and ROSAT (IAUC 5142).
The pulse profile had a strongly asymmetric shape. We did not find
any variability of the period on a timescale of 100 hr. The 3-sigma
upper limit on the period deviation was < 3 x 10E-9."
A0538-66
R. Schulte-Ladbeck, University of Wisconsin; and G. Clayton,
University of Colorado, write: "The periodic x-ray transient
A0538-66 in the Large Magellanic Cloud, also known as 0535-668,
which has been mostly in a quiescent state at visible wavelengths
for the past 7 years, appears to be active again. Spectropolarimetry
obtained around Jan. 29.45 UT (phase 0.02) by R. Schulte-Ladbeck
at the Anglo-Australian Telescope shows fairly strong emission at H-
beta and He II 468.6-nm. Continuum linear polarization is about 1
percent at p.a. about 110 deg. No photometry was done but visually
the star appeared to be in its faint state."
1991 February 4 (5180) Daniel W. E. Green
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