Central Bureau for Astronomical Telegrams
IAUC 5481: CRAB NEBULA; 1H 0857-242
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Circular No. 5481
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
CRAB NEBULA
R. Sunyaev, E. Churazov, M. Gilfanov, A. Claret, J. Ballet,
J. P. Dezalay and P. Mandrou, on behalf of the GRANAT team (IKI,
Moscow; CEA, Saclay; CESR, Toulouse), report: "Evidence for an
emission feature at about 545 keV in the spectrum of the Crab
Nebula was found with GRANAT/SIGMA on Mar. 10-11. The peak on the
image was at 5.1 sigma, and the flux in the 490-580-keV energy band
corresponded to 4.5 x 10**-3 photon s-1 cm-2. The x-ray spectrum
below 200 keV was consistent with that observed by SIGMA in 1990-1991.
The 3-sigma upper limit on the average flux in the 490-580-keV band
during the 1990-1991 observations was 1.2 x 10**-3 photon s-1 cm-2.
Searches for any unusual behavior of the source (such as a wisp or
glitch) at other wavelengths are urged."
1H 0857-242
D. de Martino, R. Gonzalez-Riestra, and P. Rodriguez,
International Ultraviolet Explorer Observatory, European Space Agency;
D. Buckley, South African Astronomical Observatory; J. Dickson,
Astronomy Department, University of Texas; and R. A. Remillard, Center
for Space Research, Massachusetts Institute of Technology, report:
"IUE observations have been made during the outburst phase of the
newly-discovered dwarf nova and likely magnetic cataclysmic variable
1H 0857-242, which on Mar. 6 was found to have brightened by more than
4 mag from its extended low state of V about 16.8. Although the
optical brightness was about the same on Mar. 7, the ultraviolet flux
shortward of 200 nm had increased by about a factor of two since the
previous day. The ultraviolet spectrum from 120 to 320 nm was
characterized by a steep continuum with strong absorption lines of N V
(124 nm), O I (130 nm), Si IV (140 nm), He II (164 nm) and N IV (172
nm). The P-Cyg profile in the C IV 155-nm line indicates outflow
velocities from 2000 km/s up to 5000 km/s. On Mar. 8 the object was
fading at a rate of 0.03 mag/hr at both ultraviolet and visual
wavelengths. On Mar. 10 the ultraviolet spectrum changed dramatically
into a flat continuum and strong emission lines of N V, Si IV and C
IV, with no sign of absorption features. The ultraviolet fluxes (in
units of 10**-14 erg cm-2 s-1 A-1) and fine-error sensor V magnitudes
were: Mar. 6.4 UT, [150 nm] not measured, [240 nm] = 6.7, V = 12.5;
7.2, 38.4, 12.8, 12.6; 8.1, 18.1, 6.8, 13.3; 8.4, 14.2, 5.0,
13.6; 10.4, 1.3, 0.7, -."
1992 March 21 (5481) Brian G. Marsden
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