Central Bureau for Astronomical Telegrams
IAUC 2793: Aql X-1; X-RAY Obs OF CYG X-1 FROM SALYUT 4
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Circular No. 2793
Central Bureau for Astronomical Telegrams
INTERNATIONAL ASTRONOMICAL UNION
Postal Address: Central Bureau for Astronomical Telegrams
Smithsonian Astrophysical Observatory, Cambridge, MA 02138, U.S.A.
Cable Address: SATELLITES, NEWYORK
Western Union: RAPID SATELLITE CAMBMASS
AQUILA X-1
A. Davidsen and colleagues (Space Sciences Laboratory, University
of California, Berkeley) and P. Sanford, P. Davison, and K. Mason
(Mullard Space Science Laboratory, University College London)
report the following pre-outburst and current optical and x-ray
data on Aql X-1 (3U 1908+00) (cf. IAU 2788): observations in the
2.5-7.5 keV band from OAO Copernicus intermittently during the past
2 years show the source present at 1-2 percent of the Crab Nebula,
significantly below the level reported in the 3U. Thirty blue and
ultraviolet plates of the field obtained during the same period,
some simultaneous with OAO Copernicus, reveal no variable stars of
amplitude greater than 0m.3 to B = 18, and no stars with significant
uv excess. The only ultraviolet object found in the vicinity is a
B = 16.6, B5v star at R.A. = 19h08m39s.3, Decl. = + 0o29' 1" (1950),
4' from the edge of the 3U error box. Spectroscopic observations
show no abnormalities. The extinction in the field appears modest
out to 10 kpc.
X-ray observations obtained between 7h and 9h UT on 1975 June
19 reveal the source at an intensity of 70 percent of the Crab Nebula,
with a significantly softer spectrum than the Crab. A blue plate
obtained during outburst at 1975 June 18.38 UT shows no change
greater than 0m.4 in any of the stars in the field to B = 17.5,
including the blue candidate mentioned above.
X-RAY OBSERVATIONS OF CYG X-1 FROM SALYUT 4
Prof. D. Ya. Martynov, Director of the Sternberg Astronomical
Institute, Moscow, reports that on 1975 June 3 E. Shaffer and
E. Moskalenko observed Cyg X-1 with an x-ray telescope on board the
space station Salyut 4 from 13h38m UT to 14h20m. From 13h38m the
2-10 keV flux was 0.28 counts/cm**2. In the 0.2-2 keV region the
x-ray flux was at the background level of 0.14 counts/cm**2. At 13h54m
the 0.2-2 keV flux rose to 0.35 counts/cm**2 and the 2-10 keV flux
increased by a factor of 1.9. Large fluctuations were observed in
this spectral region with a characteristic time of less than 10s.
At 14h10m in the 2-10 keV region a flare was observed lasting
about 20s. The maximum flare flux was about 3.9 counts/cm**2. The
characteristic rise time of the flare was less than 1s. The
observations conform to the model of a disk accretion onto a black hole.
1975 June 25 (2793) Owen Gingerich
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