Central Bureau for Astronomical Telegrams
IAUC 6478: GX 1+4; 46P
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Circular No. 6478
Central Bureau for Astronomical Telegrams
INTERNATIONAL ASTRONOMICAL UNION
Postal Address: Central Bureau for Astronomical Telegrams
Smithsonian Astrophysical Observatory, Cambridge, MA 02138, U.S.A.
IAUSUBS@CFA.HARVARD.EDU or FAX 617-495-7231 (subscriptions)
BMARSDEN@CFA.HARVARD.EDU or DGREEN@CFA.HARVARD.EDU (science)
Phone 617-495-7244/7440/7444 (for emergency use only)
GX 1+4
D. Chakrabarty, Massachusetts Institute of Technology (MIT);
M. H. Finger, Universities Space Research Association; and T. A.
Prince, California Institute of Technology, report for the Compton
Observatory BATSE team: "The accreting x-ray pulsar GX 1+4 has been
undetected by BATSE since Aug. 18, with a 90-percent-confidence
upper limit of 15 mCrab (20-60 keV) for the pulsed intensity. This
is the first time that GX 1+4 has remained below our 15-mCrab
detection threshold for longer than a month, since we began
continuous BATSE monitoring of its pulsed flux in 1991. When last
detected on Aug. 18.5 UT, the phase-averaged pulsed intensity of GX
1+4 was 29 +/- 4 mCrab and the barycentric pulse frequency was
(8.0381 +/- 0.0001) x 10E-3 Hz. The pulse frequency derivative
changed from (-3.7 +/- 0.2) x 10E-12 Hz sE-1 during May 28-June 12,
to (0.0 +/- 0.2) x 10E-12 Hz sE-1 during July 27-Aug. 6, suggesting
that a torque reversal may have occurred in early Aug. (cf. IAUC
6105, 6153). The phase-averaged pulsed intensity flared from 59
+/- 5 mCrab on June 4.5 to a maximum of 204 +/- 5 mCrab on Aug.
5.5, before dropping below our detection threshold."
W. Cui and D. Chakrabarty, MIT, write: "RXTE/PCA observations
of GX 1+4 on Sept. 5.03 UT detect a phase-averaged pulsed intensity
of 4.9 mCrab (2-60 keV) and a barycentric pulse frequency of
(8.03156 +/- 0.00042) x 10E-3 Hz, implying that the pulsar
continued to spin down after the last BATSE detection on Aug. 18,
with a mean pulse frequency derivative of (-4.3 +/- 0.3) x 10E-12
Hz sE-1. A second RXTE/PCA observation on Sept. 25.55 did not
detect any pulsations, with a 90-percent-confidence upper limit of
0.2 mCrab on the pulsed intensity. This is comparable to the low
state established by EXOSAT non-detections of GX 1+4 in 1983 and
1984 (IAUC 3872). Deeper x-ray observations and optical/infrared
observations of the red-giant companion are strongly encouraged."
COMET 46P/WIRTANEN
P. Lamy, Laboratoire d'Astronomie Spatiale, and his team
report the apparent detection of the nucleus of 46P with the Hubble
Space Telescope (+ WFPC2) on Aug. 28: "After removing the small
contribution of the (stable) coma to the central pixels, the R
magnitude of the nucleus was found to vary from 21.6 to 21.9 over
time intervals of 1.5 hr, though a clear rotational pattern is not
evident. For a geometric albedo of 0.04, the mean effective radius
is 0.58 km."
(C) Copyright 1996 CBAT
1996 September 26 (6478) Daniel W. E. Green
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