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."