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Spin period evolution of the newly identified ULX pulsar (NGC 300 ULX1) associated with the supernova impostor SN2010da

ATel #11179; G. Vasilopoulos (MPE), F. Haberl (MPE), S. Carpano (MPE), C. Maitra (MPE)
on 16 Jan 2018; 20:21 UT
Credential Certification: Georgios Vasilopoulos (gevas@mpe.mpg.de)

Subjects: X-ray, Neutron Star, Pulsar

Referred to by ATel #: 11228, 11229, 11282

Following the discovery of the newly discovered ULX pulsar in NGC 300 (ATel #11158) we searched the available X-ray data for the evolution of the spin period of the neutron star and the X-ray luminosity. Swift/XRT monitored the system between April and July 2017. The system's luminosity was found to be approximately constant at 2-4×1039 erg s-1, consistent with those reported for the XMM-Newton observations (ATel#11158).

We performed barycentric corrections to the event arrival times and searched for periodic signals. The signal with the highest significance was found from the observation performed on April 22, 2017 (obsid: 00049834010) and we infer a spin period of 26.65±0.1 s. Considering the initial spin period reported for the system (31.6 s; ATel#11158) we derive an average spin-up rate -4.6×10-7 s over 123 days. The analysis of the latest Swift observation (performed on July 12, 2017) yields a low-significance signal at 24.36 s. The long-term spin period evolution is consistent with an exponential decrease, which implies that P/Pdot is roughly constant as expected during a phase with steady accretion rate. If that trend continued the current spin period of the system would be expected around 20 s. A new Swift/XRT observation of the system has been approved, that will help us verify this prediction.

We note that the spin period detection reported in ATel#11174, is probably a multiple of the Swift/XRT frame time in PC mode, and thus an instrumental feature.

We thank the Swift team for accepting and scheduling the target of opportunity observations.