Chandra/HRC localization and pulse period measurement of 4U 1901+03
ATel #12556; Paul Hemphill (MIT), Joel Coley (Howard University/NASA-GSFC), Felix Fuerst (ESA-ESAC), Peter Kretschmar (ESA-ESAC), Matthias Kuehnel (ECAP), Christian Malacaria ( NASA-MSFC/USRA ), Katja Pottschmidt (CRESST/UMBC/NASA-GSFC)
on 7 Mar 2019; 16:26 UT
Credential Certification: Felix Fuerst (felix.fuerst@sciops.esa.int)
Subjects: X-ray, Binary, Neutron Star, Transient
The BeXRB 4U 1901+03 went into outburst around 2019-02-08 (MJD 58522, ATel#12498, GCN#23882). In order to improve the source localization, we have obtained a 2ks Chandra/HRC observation, taken on 2019-03-05 (MJD 58547.73). The source is strongly detected (~25 counts/s in the HRC) at RA 19:03:39.40, Dec +3:12:15.91, with 90% of flux contained within a radius of 1.42". This is 0.3" offset from the Swift/XRT position (ATel#12514), entirely within the 2.4" Swift localization, and nearly exactly coincident (0.1" offset) with the proposed optical counterpart, UKIDS J190339.39+031215.6 (see ATel#12554). The counting rate of 25 counts/s translates to a flux of ~2E-9 erg/cm^2/s, assuming the Gamma=0.5 spectrum reported in ATel#12514. Assuming the lower-bound distance of 12 kpc from ATel#12554, the isotropic luminosity is 3.4E37 erg/s. Pulsations are strongly detected in the barycentered, background-subtracted lightcurve at a period of 2.761 +/- 0.001 s, determined by epoch folding. This is consistent with the period of 2.762 s determined by NICER (ATel#12515) and the pulse period detected during the 2003 outburst, confirming that the target is 4U 1901+03. Applying a binary correction based on the orbital solution of Galloway et al. (2005) does not result in a significantly different pulse period. We thank the Chandra operations team for their help coordinating this observation.
