V404 Cygni

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) telex: "V404 Cyg = GS 2023+338 was observed several times during June 9-10 by the instruments of the Kvant module of the Mir space station. The source was localized at R.A. = 20h22m06s, Decl. = +33 42.2 (equinox 1950.0) with approximately 0'.4 error using the positions of Cygnus X-1 and Cygnus X-3 in the field-of-view of the Coded Mask Imaging Spectrometer (TTM). The star V404 Cyg is inside this error box. The source is significantly detected up to 300 keV by the HEXE and Pulsar X-1 instruments. It has a flat spectrum with a strong absorption and high energy exponential cut-off at energies > 100 keV. The source is strongly variable. Maximal detected fluxes are 0.1 Crab at 5 keV, 1.5 Crab at 20 keV, and 3.5 Crab at 100 keV."