SWIFT/XRT confirmed the new outburst of SAX J1808.4-3658
ATel #7371; A. Sanna (UNICA), F. Pintore (UNICA), A. Riggio (UNICA), A. D'Ai (UNICA), T. Di Salvo (UNIPA), L. Burderi (UNICA), R. Iaria (UNIPA), F. Scarano (UNICA), A. Segreto (INAF-IASF Pa)
on 11 Apr 2015; 22:57 UT
Credential Certification: Andrea Sanna (andrea.sanna@dsf.unica.it)
Subjects: X-ray, Binary, Neutron Star, Transient, Pulsar
Following the Swift/BAT discovery of a rate increase towards the direction of the accreting millisecond X-ray pulsar SAX J1808.4-3658 (Atel #7364), a 0.5ks Swift/XRT observation has been carried out in PC mode on 2015-04-11.
Using the method of Evans et al. (2009, MNRAS, 397, 1177), we found a UVOT-enhanced position of RA = 272.11503 deg, DEC = -36.97828 deg (J2000), with an associated uncertainty of 2.2 arcsec (90% c.l.). This location is consistent, within errors, with the optical position of SAX J1808.4-3658 reported by Hartman et al. (2008), confirming that the accreting millisecond X-ray pulsar started a new outburst.
The Swift/XRT PC-mode data are heavily piled-up due to the high count rate of the source (~8 cts/s). After correcting for pile-up effects, we performed a spectral analysis adopting an absorbed power-law. We found an absorption column density of 1E21 cm^-2 and a power-law photon index of 1.6 +/- 0.1. The estimated 0.3-10 keV unabsorbed X-ray flux is 2.6E-9 erg/cm^2/s.
We thank the Swift team for the prompt scheduling of the reported observations. Additional Swift/XRT observations have been requested.
