2021/02/15 by Chin-Ping Hu, Yoshihiro Ueda, Teruaki Enoto
Physics and Astronomy · #Astrophysical Phenomena and Observations #Astrophysics and Star Formation Studies #Flux (metallurgy) #Galaxy #Luminosity #Magnetic field #Orbital period #Period (music) #Pulsar #Pulsars and Gravitational Waves Research #Stars #astro-ph.HE
paper · pdf · doi:10.3847/1538-4357/abd7a5
8 pges, 4 figures, accepted for publication in ApJ
arxiv created 2021/02/15 · openalex created_date 2021/03/01 · openalex publication_date 2021/03/01 · arxiv updated 2021/03/10 · openalex updated_date 2026/08/05
Abstract We report the discovery of possible periodic X-ray dips in a pulsating ultraluminous X-ray source, M51 ULX-7, with archival Chandra observations. With ∼20 days of monitoring in the superorbital descending state, we discovered three dips with separations of ∼2 and ∼8 days via the Bayesian block technique. A phase-dispersion minimization and a test suggest that the dip is likely recurrent with a period of ∼2 days, consistent with the orbital period of M51 ULX-7. We interpret the dip as an obscuring of the emission from the pulsar by the vertical structure on the stream–disk interaction region or the atmosphere of the companion star. Both interpretations suggest the viewing angle to be ∼60°. Given that the magnetic field of M51 ULX-7 is moderately high, B ∼ 10 13 G, a low geometric beaming with is sufficient to explain the observed flux and the presence of dips. Obscuration of the stellar wind remains an alternative possible origin and further monitoring of the dips will be required.