INTEGRAL detection of renewed activity from SAX J2103.5+4545

ATel #4168; V. Sguera (INAF - IASF Bologna), S. Drave, M. Goossens, A. J. Bird (University of Southampton), L. Sidoli (INAF - IASF Milano), M. Fiocchi, A. Bazzano, A. Tarana (INAF - IASF Roma)
on 12 Jun 2012; 17:00 UT
Credential Certification: Raffaella Landi (landi@iasfbo.inaf.it)

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During recent INTEGRAL Galactic Plane Scanning observation (PI: A. Bazzano), starting on 2012 June 12 at 01:00 UTC, IBIS/ISGRI detected renewed activity from the Be HMXB SAX J2103.5+4545. The source was detected at 29 sigma level (18-60 keV) with a flux of 61 +- 2 mCrab (15 ks exposure time). This detection confirms the X-ray activity predicted by Konstantinova et al. (ATel #4068). A preliminary IBIS/ISGRI spectral analysis reveals a 18-60 keV spectrum which can be described by a power law with photon index 2.6 +- 0.2, the 18-60 keV flux is 7.6 x 10^-10 erg cm^-2 s^-1. The source was also covered by the JEM-X monitor for a total of 3.7 ks, it was detected at 10.3 sigma level (3-10 keV) with a flux of 47 +- 5 mCrab. It is worth noting that SAX J2103.5+4545 was also in the IBIS/ISGRI field of view during the previous Galactic Plane Scanning observation, starting on 2012 June 06 at 02:48 UTC, during which it was barely detected at 4.5 sigma level (11 ks exposure).

The Be/XRB transient pulsar SAX J2103.5+4545 has been observed to undergo an outburst a few times since its discovery, likely due to an increased wind from the Be companion: in 1997 (Hulleman et al. 1998), in 1999 (Baykal et al. 2000), in 2002-2004 (Sidoli et al. 2005) and in 2007 (Baykal et al. 2007, Camero-Arranz et al. 2007, Ducci et al. 2008). The last two outbursts have been observed also with INTEGRAL. The system is composed by a BOVe star (Reig & Mavromatakis 2003) and a neutron star in an eccentric orbit (e = 0.4), with an orbital period of 12.665 days (Camero-Arranz et al. 2007), the shortest known in a Be/XRB. The neutron star spin period (about 358 s) implies that SAX J2103.5+4545 does not follow the correlation between the orbital and spin periods in Be/XRBs (Corbet 1986).