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IAUC 6393: GRO J1655-40; C/1996 B2; FG Sge

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                                                  Circular No. 6393
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)


GRO J1655-40
     R. Remillard, H. Bradt, W. Cui, A. Levine, E. Morgan, B.
Shirey, and D. Smith, Massachusetts Institute of Technology, report:
"Observations with the RXTE All Sky Monitor (ASM) reveal a recent
recurrence of bright x-ray emission from GRO J1655-40, a dynamical
blackhole binary (Bailyn et al. 1995, Nature 378, 157) that began
x-ray eruptions during 1994 and became a source of relativistic
radio jets (Tingay et al. 1995, Nature 374, 141).  Combining the
ASM measurements at 2-12 keV in 1-day time bins (UT), we see an
upper limit of 12 mCrab (3 sigma) on 1996 Apr. 23, followed by
detections of 71 +/- 15 mCrab on Apr. 25, 420 +/- 30 mCrab on Apr.
26, 586 +/- 15 mCrab on Apr. 27, 802 +/- 9 mCrab on Apr. 28, and
1077 +/- 30 mCrab on Apr. 29.  Between Apr. 30 and May 5, the x-ray
flux ranges between 1.3 and 1.5 Crab.  Observations at all
wavelengths are strongly encouraged."


COMET C/1996 B2 (HYAKUTAKE)
     F. E. Marshall, C. Lisse, M. Mumma, and R. Petre, NASA Goddard
Space Flight Center; and K. Dennerl, J. Englhauser, and J. Trumper,
Max-Planck-Institut fur Extraterrestrische Physik, Garching, report:
"The x-ray emission from comet C/1996 B2 is primarily at energies <
2 keV.  No evidence for emission in the band 2-10 keV was seen
during a fortuitous scan lasting 24 s across the comet on Mar.
31.2836 UT with the Proportional Counter Array onboard the Rossi X-
ray Timing Explorer.  The 90-percent-confidence upper limit for the
flux in the band 2-10 keV, assuming a power-law spectrum with
photon index 2.0, is 1.6 x 10E-11 erg sE-1 cmE-2.  The limit is 1.7
x 10E-11 erg sE-1 cmE-2 for an index of 3.0.  During this
observation, the comet was 0.22 AU from the earth and 0.91 AU from
the sun.  Assuming the comet's luminosity in the band 0.1-2 keV was
the same as during the non-flaring intervals of the ROSAT
observation on Mar. 26-28 (IAUC 6373), we can rule out spectral
shapes harder than a power law with photon index 2.0 or thermal
bremsstrahlung emission with a temperature of 2.5 keV.  For both
these assumed spectral shapes, > 50 percent of the 0.1- to 10-keV
luminosity is at energies < 1.25 keV."


FG SAGITTAE
     S. Shugarov, Sternberg Astronomical Institute, Moscow, reports
that this variable has faded to mag V about 16 and B about 17 on
Apr. 24.04 UT.  A CCD image by R. Royer, Lakewood, CA, yields mag
16-16.5 on May 7.36.

                      (C) Copyright 1996 CBAT
1996 May 8                     (6393)            Daniel W. E. Green

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