Swift/BAT detected a possible new outburst of the X-ray transient SAX J1808.4-3658
ATel #7364; A. Sanna (UNICA), A. Riggio (UNICA), F. Pintore (UNICA), A. D'Ai (UNICA), T. Di Salvo (UNIPA), L. Burderi (UNICA), R. Iaria (UNIPA), F. Scarano (UNICA), A. Segreto (INAF-IASF Pa)
on 10 Apr 2015; 20:51 UT
Credential Certification: Andrea Sanna (andrea.sanna@dsf.unica.it)
Subjects: X-ray, Transient
The Swift/BAT X-ray monitor detected a significant rate increase from the direction of the accreting millisecond X-ray pulsar SAX J1808.4-3658 starting on 2015 April 9 (MJD 57121), with a count rate of 0.009 +/- 0.001 counts/s/cm2. Assuming a power-law spectral shape with photon index of 2 and neutral absorption of 2E+21 cm^-2 (Papitto et al. 2009, Cackett et al. 2009), the observed flux corresponds to ~4E-9 erg/s/cm2 in the 2-20 keV energy range, consistent with the beginning of the 2008 outburst (Cackett et al. 2009).
The Swift/BAT result is based on the coordinates of SAX J1808.4-3658 (RA = 272.115 deg ; Dec= -36.979 deg), however, the detector angular resolution of ~3 arc minutes is not sufficient to distinguish this source from other nearby objects.
A Swift/XRT target of opportunity observation has been requested to verify the Swift/BAT detection, and to confirm the possible association with the X-ray transient SAX J1808.4-3658.
