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.
International Astronomical Union Circular
- Pub Date:
- March 1976