Outburst Evolution and Pulse Period of 1A 0535+262
ATel #557; D. M. Smith, B. Hazelton, (U. C. Santa Cruz), W. Coburn, S. E. Boggs, M. Fivian, G. J. Hurford, H. S. Hudson (U. C. Berkeley), B. Grefenstette, R. Gilmore (U. C. Santa Cruz)
on 7 Jul 2005; 03:39 UT
Credential Certification: David M. Smith (dsmith@ssl.berkeley.edu)
Subjects: X-ray, Binary, Neutron Star, Transient, Pulsar
Referred to by ATel #: 595, 601
The Reuven Ramaty High Energy Solar Spectroscopic Imager (RHESSI)
spacecraft was pointed to the accreting pulsar 1A 0535+262 after the
discovery by Tueller et al. (ATEL #504) that it was in a major
outburst for the first time since 1994. Operations to point away from
the Sun began on 3 June and the pulsar gradually moved into our field
of view over the next week (RHESSI repointing is very slow since the
spacecraft spins near 15 rpm and has only magnetic torquers to repoint
it). The best data were obtained between 11 June and 24 June 2005.
The data for several days before this interval may also prove to be
useful, but at reduced sensitivity. Comparison with RHESSI
observations of the Crab in June 2004 show that 1A 0535+262 had a flux
of about 4.5 Crab on 12 June and 2.4 Crab on 23 June, measured at 30
keV. These results, combined with the Swift report (ATEL #504) that
the outburst became detectable on May 16 and rose to > 3 Crab before
May 31, suggest that this outburst, while probably in decline, is
lasting somewhat longer than the last major outburst in 1994, which
had a duration (full width at 1/10 peak flux) of about 35 days
(Finger, Wilson and Harmon 1996, ApJ 459, 288). Our measured pulse
period from 15 June to 24 June was 103.40(2)s, consistent with the
value of 103.41s obtained by Mukherjee and Paul (2005, A&A 431, 667)
with BeppoSAX in 2001.