SGR1900+14

Among the four SGRs confirmed today, SGR 1900+14is peculiar for the absence of a surrounding supernova remnant (however, close to the recently determined position a less than 10⁴ years old supernova remnant, G42.8+0.6, lies. Three outbursts of moderate intensity from this source were first detected in 1979. The source was detected again in 1992 and in May 1998. ASCA and RXTE observations after the May 1998 activity revealed a periodicity of 5.16 s in the quiescent X-ray (2-10 and 2-20 keV, respectively) emission with period derivative $\sim 1 \times 10^{-10} \rm s \, s^{-1}$.On 1998 August 27 a very strong outburst from SGR 1900+14was detected by Konus-Wind, Ulysses and BeppoSAX . The 5.16 s periodicity was unambiguously detected during the outburst. Transient emission was also detected in the radio band with the Very Large Array radiotelescope: a previously unknown radio source appeared in the error box of SGR 1900+14on 1998, September 3 and faded away in less than one week. These observational elements support an interpretation of these phenomena in the framework of the magnetar model .