NICER Observations of the 2018 Outburst of XTE J1810−197

Creators: Güver, Tolga; Göğüş, Ersin; Vurgun, Eda; Enoto, Teruaki; Gendreau, Keith C.; Sakamoto, Takanori; Gotthelf, Eric V.; Arzoumanian, Zaven; Guillot, Sebastien; Jaisawal, Gaurava K.; Malacaria, Christian; Majid, Walid A.

Abstract

We present the earliest available soft X-ray observations of XTE J1810−197, the prototypical transient magnetar, obtained 75–84 days after its 2018 outburst with the Neutron Star Interior Composition Explorer. Using a series of observations covering eight days we find that its decreasing X-ray flux is well described by either a blackbody plus power law or a two-blackbody spectral model. The 2–10 keV flux of the source varied from (1.206 ± 0.007) × 10^(−10) to (1.125 ± 0.004) x 10^(-10) erg s^(-1) cm ^(-2) , a decrease of about 7% within our observations and 44% from that measured 7–14 days after the outburst with NuSTAR. We confirm that the pulsed fraction and spin pulse phase of the neutron star are energy dependent up to at least 8 keV. Phase-resolved spectroscopy of the pulsar suggests magnetospheric variations relative to the line of sight.

Additional Information

© 2019 The American Astronomical Society. Received 2019 April 16; revised 2019 May 6; accepted 2019 May 10; published 2019 May 30. We thank Wynn C.G. Ho for careful reading and insightful comments on this manuscript. E.V.G. acknowledges NASA grant No. 80NSSC18K0452. T.E. was supported by JSPS grant No. 16H02198 and 18H01246. This work was supported by NASA through the NICER mission and the Astrophysics Explorers Program. This research has made use of data and software provided by the High Energy Astrophysics Science Archive Research Center (HEASARC), which is a service of the Astrophysics Science Division at NASA/GSFC and the High Energy Astrophysics Division of the Smithsonian Astrophysical Observatory. Facility: NICER. -

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