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SWIFT/BAT possible detection of a new outburst from Aql X-1

ATel #9287; A. Sanna (UNICA, Italy), A. Riggio (UNICA, Italy), F. Pintore (IASF-MI, Italy), D. Altamirano (Southampton), L. Burderi (UNICA, Italy), T. Di Salvo (UNIPA, Italy)
on 31 Jul 2016; 10:47 UT
Distributed as an Instant Email Notice Transients
Credential Certification: Alessandro Riggio (riggio@dsf.unica.it)

Subjects: X-ray, Binary, Neutron Star, Transient, Pulsar

Referred to by ATel #: 9292, 9293, 9306

The Swift/BAT X-ray monitor observed significant X-ray activity from the direction of the accreting millisecond X-ray pulsar Aql X-1 starting on 2016 July 29 (MJD 57598), with a count rate of 0.0011 +/- 0.003 counts/s/cm^2. This activity is consistent with what reported by MAXI transient alert started on 2016 July 28 (Ground Trigger ID: 7597076265). Assuming a power-law spectral shape with photon index of 2.2 and neutral absorption of 1E+22 cm^-2 (Atel #6286, #7095), the observed flux corresponds to ~6E-10 erg/s/cm2 in the 0.3-10 keV energy range, consistent with the beginning of the previous outbursts (Atel #6286, #7088). The Swift/BAT result is based on the coordinates of Aql X-1, 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. Multi-wavelength observation of the source are strongly encouraged.