Nova Herculis 1991

P. Predehl, J. H. M. M. Schmitt and J. Trumper, Max-Planck- Institut fur Extraterrestrische Physik; T. J. O'Brien, H. M. Lloyd and M. F. Bode, Lancashire Polytechnic; and M. G. Watson and K. A. Pounds, Leicester University, communicate: "This nova was observed with the XRT/PSPC of ROSAT on Mar. 30.46 UT, five days after discovery (IAUC 5222). A total of 194 counts were detected within the observation time of 1235 s, yielding a countrate of 0.16 +/- 0.01 cts/s. According to its spectrum, the source seems to be highly absorbed with a low-energy cutoff at approximately 1 keV. This constitutes the first x-ray detection of a classical nova at or near maximum. Previous observations of classical novae at this stage with SAS 3, Ariel V and EXOSAT have only resulted in upper limits on their x-ray flux. The region of the nova was already observed in the ROSAT all-sky survey during 1990 Sept. 25-28. The data indicate that there was no source present at this position with an upper limit of approximately 0.01 cts/s."