We present interplanetary network localization, spectral, and time history information for 7 episodes of exceptionally intense gamma-ray emission from Cygnus X-1. The outbursts occurred between 1995 and 2003, with durations up to ∼28000 seconds. The observed 15 -300 keV peak fluxes and fluences reached 3 × 10 −7 erg cm −2 s −1 and 8 × 10 −4 erg cm −2 respectively. By combining the triangulations of these outbursts we derive an ∼ 1700 square arcminute (3 σ) error ellipse which contains Cygnus X-1 and no other known high energy sources.The outbursts reported here occurred both when Cyg X-1 was in the hard state as well as in the soft one, and at various orbital phases. The spectral data indicate that these outbursts display the same parameters as those of the underlying hard and soft states, suggesting that they represent another manifestation of these states.Subject headings: black hole physics -stars: individual (Cygnus X-1)

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The newly discovered X-ray transient XTE J1810-197 exhibits almost all characteristics of magnetars. It possesses a relatively long spin period of 5.54 s and a rapid spin down rate of § 10¨1 1 s s¨1, while showing no evidence for Doppler shifts due to a binary companion. This yields a magnetar-strength dipole field B © 3 10 14 G and a young characteristic age τ 7600 yr. The spectrum of the source is notably soft (photon index § 4) and optical observations with the 1.5 m Russian-Turkish Optical Telescope RTT150 revealed a limiting magnitude of R c © 21 5, both consistent with those of Soft gamma repeaters and anomalous X-ray pulsars. However, the source shows a significant flux decline for over nine months and is present in archival ASCA and ROSAT observations at nearly two orders of magnitude fainter luminosity. Putting all evidence together shows that we have found the first confirmed transient magnetar. This suggests the presence of other unidentified transient magnetars in a state similar to XTE J1810-197 in its inactive phase. The detection of such sources is one of the important areas in which future X-ray timing missions can make a significant impact.