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INTEGRAL detects a new outburst of MXB 0656-072

ATEL # 1281; I. Kreykenbohm (IAA Tuebingen/ISDC), S. E. Shaw (University of Southampton/ISDC), Valentina Bianchin (INAF/IASF-Bologna), R. Diehl (MPE Garching), S. Brandt (DNSC Copenhagen), M. Mas-Hesse (LAEFF, Madrid), A. Parmar (ISOC Madrid), W. Hermsen (SRON, Utrecht), R. Krivonos (IKI Moscow/MPA Garching)
on 15 Nov 2007; 14:32 UT
Distributed as an Instant Email Notice (Request for Observations)
Password Certification: Nami Mowlavi (Nami.Mowlavi@obs.unige.ch)

Subjects: X-ray, Gamma Ray, Request for Observations, Binaries, Neutron Stars, Pulsars, Transients
Referred to by ATEL #: 1283, 1293, 1303

The recurrent X-ray transient pulsar "MXB 0656-072" (also known as XTE J0658-073, ATELs 197, 199, 200, 202, McBride et al. 2006) has begun another outburst about four years after the previous outburst in October 2003. On November 10 (MJD 54414.9, begin of Integral revolution 620) the source was first detected in ISGRI with a count rate of 6.9 +/- 0.8 counts per second between 20 and 40 keV (corresponding to 40 mCrab). The source was clearly detected in a single science window (SCW-ID 062000020010) with a detection significance of 9 sigma. Since then the source was observed repeatedly in 20 mostly non-consecutive science windows until the end of the revolution. The observed count rate was between 4 and 12 counts per second (20 to 70 mCrab) and the source was detected with a significance between 6 and 16 sigma. The source was not detected above 40 keV. JEM-X clearly detected the source when the source was in its field of view with up to 2.6 counts per second (3 to 10 keV) and with a significance up to 22 sigma. Preliminary spectral analysis of the ISGRI data shows that the spectrum of the source is very soft with a spectral index of 4.3 +/- 0.3. Temporal analysis shows that the source is strongly pulsating with a period of 160.0 seconds. The single peaked pulse profile exhibits a large pulsed fraction of 50%. Although the source was detected more frequently towards the end of the revolution, the average flux did not increase significantly, it is therefore very hard to predict the evolution of this outburst. Further observations are therefore strongly encouraged. Plots are available at http://isdc.unige.ch/~kreyken/mxb0656


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