Swift/XRT confirms the new outburst of Aql X-1
ATel #9292; A. Sanna (UNICA), A. Riggio (UNICA), F. Pintore (IASF-MI), D. Altamirano (Southampton), L. Burderi (UNICA), T. Di Salvo (UNIPA)
on 1 Aug 2016; 10:51 UT
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Credential Certification: Andrea Sanna (firstname.lastname@example.org)
Subjects: X-ray, Binary, Neutron Star, Transient, Pulsar
Triggered by the X-ray enhancement observed by Swift/BAT on 2016 July 29 at a position compatible with the low mass X-ray binary Aql X-1 (Atel #9287), a 500 s observation with Swift/XRT was promptly carried out. Swift/XRT operating in Photon Counting mode detected a single bright X-ray source.
The XRT location is (J2000): RA=287.8178° DEC=0.5848° with an error radius of 3.5'' (90% c.l.). This position is consistent with that of the transient low mass X-ray binary Aql X-1.
Approximately 45 source counts per second were detected during the ~500 s observation. This implies that pile-up is affecting the source spectral properties. To extract the spectrum we used the XRT on-line tool at http://www.swift.ac.uk (see Evans et al. 2009, MNRAS, 397, 1177), that applies standard pile-up corrections. We fitted the spectrum with an absorbed power-law model with N_H=0.4+/-0.1 10^22 cm^-2 and photon index 1.2+/-0.1, likely implying that the source is in a hard state. The observed 0.3-10 keV X-ray flux is 2.9E-9 erg/cm^2/s suggesting that Aql X-1 entered in a new outburst phase.
More observations will be requested to follow up the outburst evolution. Multi-wavelength observations of the source are strongly encouraged.