Spectral evolution of X-ray pulsar 4U 1901+03 during the 2019 outburst based on Insight-HXMT and NuSTAR observations

• Main Authors: Nabizadeh, Armin, Tsygankov, Sergey S, Ji, Long, Doroshenko, Victor, Molkov, Sergey V, Tuo, Youli, Zhang, Shuang-Nan, Lu, Fan-Jun, Zhang, Shu, Poutanen, Juri
• Format: Journal Article
• Language: English
• Published: 09-06-2021
• Subjects: Physics - High Energy Astrophysical Phenomena
• DOI: 10.48550/arxiv.2005.14555

A&A 652, A89 (2021) We report on a detailed spectral analysis of emission from X-ray pulsar 4U
1901+03 using data obtained by the Insight-HXMT and NuSTAR observatories during
the 2019 outburst of the source. Thanks to the extensive coverage of the
outburst by Insight-HXMT, we were able to investigate the spectral evolution of
the source as a function of flux, and compare these results to the previous
reports, focusing on the properties of a putative absorption feature at around
10 keV. In particular, we demonstrate that the broadband X-ray continuum of 4U
1901+03 can be well described with a two-component continuum model without an
absorption line at 10 keV, which casts doubt on its interpretation as a
cyclotron line. The high quality of the data also allowed us to perform both
phase-averaged and phase-resolved spectral analyses as a function of
luminosity. Finally, we performed a detailed investigation of another
absorption feature in the spectrum of the source around 30 keV recently
reported in the NuSTAR data. We show that this feature appears to be
significantly detected both in phase-averaged and phase-resolved spectra
irrespective of the continuum model.