Central Bureau for Astronomical Telegrams
IAUC 4769: A0535+26
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Circular No. 4769
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
A0535+26
F. Makino and the Ginga Team telex the following additional
x-ray intensities measured with the Ginga All Sky X-Ray Monitor
(cf. IAUC 4768): Mar. 31.17 UT, 0.45 Crab; Apr. 1.17, 0.49 Crab.
The source was observed with the Large Area Counters (LAC) for 13
min beginning Apr. 4.25, with the x-ray intensity being about 0.6
Crab and the apparent pulse period being 103.4 +/- 0.3 s.
W. Cook, J. Grunsfeld, W. Heindl, D. Palmer, T. Prince, S.
Schindler, and E. Stone, California Institute of Technology, report:
"Hard x-ray and gamma-ray observations of the Crab Nebula/A0535+26
region were made during the period Apr. 4.2-4.5 UT with the Caltech
Imaging Gamma-ray Spectrometer launched by balloon from Alice Springs,
Australia. Preliminary analysis of 1.3 hr of data has given strong
detections of both A0535+26 and the Crab nebula and pulsar. Our
observations follow the detection of activity from A0535+26 in the
1- to 6-keV band by Ginga on Mar. 28 and 30 (IAUC 4768) and indicate
that A0535+26 is undergoing a giant outburst with hard x-ray flux
levels similar to those observed in 1975 and 1980. The pulse-phase
averaged flux from A0535+26 is estimated at 2.4 +/- 0.5 Crab in the
energy interval from 23 to 52 keV, 0.6 +/- 0.1 Crab from 52 to 103 keV,
and < 0.2 Crab (2 sigma) from 103 to 176 keV."
R. Sunyaev and the Kvant Team (Space Research Institute,
U.S.S.R. Academy of Sciences; Birmingham University; Netherlands Space
Research Organization, Utrecht; Max-Planck-Institut fur
Extraterrestrische Physik; and Astronomisches Institut, University of
Tubingen) communicate: "On Apr. 8 and 9, the transient source
A0535+26 was observed by the Mir-Kvant-Rontgen Observatory. The Coded
Mask Imaging Spectrometer TTM has the Crab nebula in the same field-
of-view. Direct comparison gives the following intensities of the
transient in various bands: 2-6 keV, 0.6 Crab; 6-10 keV, 1.5 Crab;
10-16 keV, 2.5 +/- 0.2 Crab; 16-26 keV, 4.3 +/- 1 Crab. The observed
energy spectrum is approximately flat in the 2- to 26-keV band. The
pulsation period was 103.267 +/- 0.003 s. The average flux in six
sessions over 10 hr on Apr. 9 (700 s each) did not reveal long-term
flux variations > 10 in the 2- to 26-keV energy band. The hard x-ray
detectors HEXE and Pulsar X-1 detected significant x-ray flux up to
100 keV. The source was 3.9 times brighter than the Crab in the 30-
to 40-keV band. Figures for the range 70-100 keV were obtained using
a Bremsstrahlung approximation for the observed spectrum in the band
2-100 keV."
1989 April 11 (4769) Daniel W. E. Green
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