Central Bureau for Astronomical Telegrams
IAUC 2879: INTENSE X-RAY BURSTS FROM A GLOBULAR CLUSTER; Cyg X-1; 1975c; 1973 I; 1973 XII
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Circular No. 2879
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
INTENSE X-RAY BURSTS FROM A GLOBULAR CLUSTER
J. Grindlay, Center for Astrophysics, Harvard and Smithsonian
Observatories; and J. Heise, Laboratory for Space Research, Utrecht,
report the detection of two intense x-ray bursts from the x-ray
source 3U 1820-30 associated with the globular cluster NGC 6624.
These events appear to be qualitatively different from short-term
variations previously reported in cosmic x-ray sources. The bursts
were detected by both the 1-30 keV (HXX) Cambridge detectors and
the 1-6 keV (SXX) Utrecht experiments on ANS on Sept. 28 at
1h31m51s and 9h49m40s UT. In the first event, the source intensity
increased by a factor of 20 in about 1 s and decayed approximately
exponentially over the next 10 s. The second burst was detected in
a region of very low and constant background as a factor of 30
increase (less than 0.5-s rise time) in source intensity, lasting
about 2 s and followed by a decay-time constant nearly identical
with that of the first event. They can exclude the possibility
that these were particle-induced events since the background
counters showed no detectable increase and the 10' x 3o collimators of
the HXX experiment yielded a direction for the bursts within 1' of
3U 1820-30 and the nucleus of NGC 6624. During the total exposure
of three hours in pointings on the source between Sept. 27.4 and
30.7, the source intensity was otherwise constant at about 3.5
cts/s or about one-quarter of the similarly constant flux observed
during three hours of ANS pointings between Mar. 24.4 and 28.0. No
bursts were detected during this first observation period, during
which the source x-ray luminosity was near the Uhuru value of about
10**38 erg/s. The peak luminosity during the bursts was thus near
l0**39 erg/s. Although the time profile resembles that of gamma bursts
the spectra were much softer (~ 10 keV exponentials). Given the
detection of two such events in six hours of observing, further
monitoring of globular-cluster x-ray sources at x-ray, optical and
radio wavelengths is needed.
CYGNUS X-1
S. S. Holt, L. J. Kaluzienski, E. A. Boldt and P. J.
Serlemitsos, Goddard Space Flight Center, report that the present
Cyg X-1 increase (IAUC 2863) shows no sign of decay after more than
one month of continuous interrogation by the Ariel 5 all-sky monitor.
Previous increases in May and September did not last much
longer than one week, and the x-ray intensity started decaying
after a few days. Cyg X-1 may therefore have returned to a long-term
high-intensity level similar to that prior to the 1971 transition.
Its present average intensity is approximately 1.5 times
that of the Crab Nebula in the energy range 3-6 keV.
PERIODIC COMET KOHOUTEK (1975c)
The following precise positions were obtained by G. Schwartz,
C. Y. Shao and R. E. McCrosky at the Harvard Observatory's Agassiz
Station. Measurer: Shao. The Apr. 1 image was trailed. On Apr.
29 and May 9 there was a strong condensation embedded in a small,
diffuse coma.
1975 UT R. A. (1950) Decl. m2 Observer
Apr. 1.07554 6 02 03.88 +20 18 30.4 Schwartz
29.08907 7 15 32.16 +18 34 06.7 14.5-15 Shao
May 9.06368 7 40 16.68 +17 34 08.5 15.5 McCrosky
30.08625 8 29 36.09 +14 56 12.6 "
PERIODIC COMET GEHRELS 1 (1973 I)
E. Roemer, University of Arizona, communicates the following
precise positions. Measurers: D. J. Granrath (first eight plates)
and C. C. McCarthy (last two plates).
1972/73 UT R. A. (1950) Decl. Note
Dec. 3.07917 0 48 42.11 + 9 00 43.0 1
3.12292 0 48 42.33 + 9 00 50.7 1
13.06806 0 50 50.84 + 9 33 30.5 2
13.08472 0 50 51.15 + 9 33 34.4 2
Jan. 1.10069 1 00 37.00 +11 02 59.3 1
1.14583 1 00 38.79 +11 03 14.1 1
29.09850 1 26 10.82 +14 06 05.4 2
29.12176 1 26 12.34 +14 06 15.4 2
Sept.23.43420 7 42 57.84 +30 21 38.5 2
23.48038 7 43 00.90 +30 21 35.4 2
Note 1: Lunar and Planetary Laboratory's 154-cm reflector.
Note 2: Steward Observatory's 229-cm reflector. L. M. Vaughn
assisted on Dec. 13, J. Q. Latta on Jan. 29, G. Reskin on Sept. 23.
COMET KOHOUTEK (1973 XII)
C. Torres, University of Chile, provides the following precise
position, obtained with the Maksutov astrograph at Cerro El Roble:
1973 UT R. A. (1950) Decl.
Dec. 5.34332 14 05 38.58 -21 48 29.9
1975 December 8 (2879) Brian G. Marsden
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