Central Bureau for Astronomical Telegrams
IAUC 2932: X-RAY BURSTS
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Circular No. 2932
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
X-RAY BURSTS
K. O. Mason, S. J. Bell Burnell and N. E. White, Mullard Space
Science Laboratory, report that the Ariel 5 collimated proportional
counter experiment has detected recurrent sequences of periodic
pulses from an area of sky of radius 5o centered on R.A. = 17h27m, Decl.
= -33o.5 (equinox 1950.0). The observations were made during Mar.
10.62-10.63 and 10.69-10.70 UT in the energy range 2-7 keV. Pulses
occur every 17s in pulse trains lasting between 1 and 3 min. Individual
pulses typically last for a few seconds and have a maximum
intensity (uncorrected for collimator response) of about 20 times
that of the Crab Nebula. The phase of the pulses is not maintained
between trains, consecutive trains being separated by as little as
1.5 17s periods. The field of view includes 3U 1727-33, MX1716-31,
MXB1730-335 and MXB1728-34.
G. Clark, Massachusetts Institute of Technology, reports that
the SAS-3 Group observed 19 x-ray bursts during Mar. 11.71-15.65 UT
from a 12o FWHM field of view that contains NGC 6624. The spectral
and temporal characteristics of these bursts are uniform and resemble
closely those described on IAUC 2907. The occurrence times of
these recent bursts are clearly not periodic, but the intervals
between bursts strongly cluster around 0d.12 (rather than the 0d.18 of
May 1975). No bursts were detected during Mar. 15.65-22.0 UT.
J. Grindlay and H. Gursky, Center for Astrophysics, report
detection of a source of x-ray bursts in Norma. Two bursts were
detected by Uhuru on 1971 Dec. 22.811 and 23.587 UT. The two lines
of position intersect in a ~ 0o.7 x 7o band centered at R.A. = 16h12m,
Decl. = -52o18' (equinox 1950.0) and perpendicular to the galactic
plane at l = 331o.2 +/- 0o.35, b = -1o.3 +/- 3o.5. The source is
presumably the one detected by the Vela satellites in 1969 (Belian et al.,
preprint); a transient source that brightened significantly in Nov.
1975 is in the same region of the sky (IAUC 2859). The rising
portion of both bursts was detected (risetimes ~ 1s.5), and the maximum
intensities were respectively ~ 1 and ~ 1.5 times the Crab. The
burst decay time constants were both about 30-100s; no enhanced
emission was seen during transits of the source either 300s before
or 300s after the events. The burst spectrum was observed to harden
significantly from kT ~ 10 keV to >~ 20 keV during the burst
decay with no change in low-energy cutoff. These characteristics
are similar to those reported for other x-ray bursts.
1976 March 26 (2932) Brian G. Marsden
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