Central Bureau for Astronomical Telegrams
IAUC 6404: Cyg X-1 AND GRS 1915+105; C/1990 N1; C/1996 E1
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Circular No. 6404
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)
CYGNUS X-1 AND GRS 1915+105
W. Cui, Center for Space Research, Massachusetts Institute of
Technology, reports for the RXTE/ASM team: "Observations with the
RXTE All Sky Monitor (ASM) reveal that Cygnus X-1 is in a bright
flaring state. It was measured at about 0.5 Crab (2-12 keV) before
it started to brighten on May 10. The intensity reached about 1
Crab on May 17 and about 2 Crab on May 19. Another blackhole
candidate, GRS 1915+105, has also become very bright. Early this
year, this source was in a highly variable state (IAUC 6392). Its
peak-to-peak amplitude became about a factor of 2 smaller between
Apr. 7 and May 17, and its mean brightness decreased linearly. It
was measured at about 0.8 Crab on May 17 and has since brightened,
reaching about 3 Crab on May 19."
COMET C/1990 N1 (TSUCHIYA-KIUCHI)
K. Dennerl, J. Englhauser, and J. Trumper, Max-Planck-Institut
fur Extraterrestrische Physik, Garching, communicate: "X-ray
emission from comet C/1990 N1 (= 1990i = 1990 XVII) was detected in
data obtained with the Positional Sensitive Proportional Counter
(PSPC) of ROSAT during the all-sky survey. Between 1990 Nov. 18.76
and 20.36 UT (when Delta = 1.08 AU, r = 1.38 AU, and visual m1
about 7.0), the PSPC was scanning across the comet, yielding a
total exposure of 500 s. The x-ray image, corrected for the
comet's motion, shows an extended source at the expected position,
with a radial extent of at least 10', or 470 000 km. This PSPC
observation allows, for the first time, spectroscopic studies of
the x-ray radiation of a comet. The spectrum can be modelled by
thermal bremsstrahlung emission with kT = 0.4 +/- 0.1 keV.
Inclusion of the 525-eV oxygen-fluorescence line improves the
confidence of the fit. Pure line emission due to oxygen and carbon
fluorescence can be ruled out. The 0.1- to 2.4-keV x-ray
luminosity was 2.5 x 10E16 erg/s and thus comparable to that of
comet C/1996 B2 (cf. IAUC 6373). The optical luminosity of C/1990
N1, however, was lower by a factor of 15 than that of C/1996 B2.
This second x-ray detection of a comet indicates that x-ray
emission is a class property of such objects."
COMET C/1996 E1 (NEAT)
Visual m1 estimates by K. Sarneczky, Raktanya, Hungary (0.44-m
reflector): Apr. 20.84 UT, 13.4; May 18.88, 13.7.
(C) Copyright 1996 CBAT
1996 May 21 (6404) Daniel W. E. Green
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