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Chandra Detection of 4U1901+03 in Quiescence

ATel #12519; J. P. Halpern (Columbia U.), A. M. Levine (MIT)
on 18 Feb 2019; 23:05 UT
Credential Certification: Jules Halpern (jules@astro.columbia.edu)

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

Referred to by ATel #: 12554, 12560

Following the localization of the X-ray binary pulsar 4U1901+03 by the Swift XRT (Mereminskiy et al. ATel #12514), we examined a 4 ks archival Chandra ACIS-I image of the region obtained by one of us (Levine) on 2009 August 19, before the position was precisely known. We find three good events likely produced by X-ray photons of energies 1.2-1.6 keV in a 1" radius circle, with centroid position (J2000) 19h 03m 39.42s, +03d 12' 15.8". This location is consistent with the Swift XRT position as well as the position of the suggested optical/IR counterpart (Mereminskiy et al. ATel #12514, Jaisawal et al. ATel #12515). The estimated 0.5-10 keV background for this region of the image is 0.026 counts in a 1" radius circle, implying that the Poisson probability of finding 3 or more background counts by chance at this location is 3e-6. Using Chandra PIMMS, the estimated absorbed flux in the 0.5-10 keV band is (2-4)e-14 erg cm^-2 s^-1. This is assuming NH=3e22 cm^-2 and photon index in the range 0 < Gamma < 1.5. The candidate Be star referenced above, #417 of Reig and Milonaki (2016), is also detected in Pan-STARRS. Optical spectroscopy to test it for H-alpha emission is feasible.