An Evolving Broad Iron Line from the First Galactic Ultraluminous X-Ray Pulsar Swift J0243.6+6124

We present a spectral study of the ultraluminous Be/X-ray transient pulsar Swift J0243.6+6124 using Neutron Star Interior Composition Explorer (NICER) observations during the system's 2017-2018 giant outburst. The 1.2-10 keV energy spectrum of the source can be approximated with an absorbed cut...

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Main Authors: Jaisawal, Gaurava K. (Author), Wilson-Hodge, Colleen A. (Author), Fabian, Andrew C. (Author), Naik, Sachindra (Author), Chakrabarty, Deepto (Author), Kretschmar, Peter (Author), Ballantyne, David R. (Author), Ludlam, Renee M. (Author), Chenevez, Jérôme (Author), Altamirano, Diego (Author), Arzoumanian, Zaven (Author), Fürst, Felix (Author), Gendreau, Keith C. (Author), Guillot, Sebastien (Author), Malacaria, Christian (Author), Miller, Jon M. (Author), Stevens, Abigail L. (Author), Wolff, Michael T. (Author)
Other Authors: MIT Kavli Institute for Astrophysics and Space Research (Contributor)
Format: Article
Language:English
Published: American Astronomical Society, 2021-02-05T21:40:55Z.
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Online Access:Get fulltext
LEADER 02879 am a22003733u 4500
001 129696
042 |a dc 
100 1 0 |a Jaisawal, Gaurava K.  |e author 
100 1 0 |a MIT Kavli Institute for Astrophysics and Space Research  |e contributor 
700 1 0 |a Wilson-Hodge, Colleen A.  |e author 
700 1 0 |a Fabian, Andrew C.  |e author 
700 1 0 |a Naik, Sachindra  |e author 
700 1 0 |a Chakrabarty, Deepto  |e author 
700 1 0 |a Kretschmar, Peter  |e author 
700 1 0 |a Ballantyne, David R.  |e author 
700 1 0 |a Ludlam, Renee M.  |e author 
700 1 0 |a Chenevez, Jérôme  |e author 
700 1 0 |a Altamirano, Diego  |e author 
700 1 0 |a Arzoumanian, Zaven  |e author 
700 1 0 |a Fürst, Felix  |e author 
700 1 0 |a Gendreau, Keith C.  |e author 
700 1 0 |a Guillot, Sebastien  |e author 
700 1 0 |a Malacaria, Christian  |e author 
700 1 0 |a Miller, Jon M.  |e author 
700 1 0 |a Stevens, Abigail L.  |e author 
700 1 0 |a Wolff, Michael T.  |e author 
245 0 0 |a An Evolving Broad Iron Line from the First Galactic Ultraluminous X-Ray Pulsar Swift J0243.6+6124 
260 |b American Astronomical Society,   |c 2021-02-05T21:40:55Z. 
856 |z Get fulltext  |u https://hdl.handle.net/1721.1/129696 
520 |a We present a spectral study of the ultraluminous Be/X-ray transient pulsar Swift J0243.6+6124 using Neutron Star Interior Composition Explorer (NICER) observations during the system's 2017-2018 giant outburst. The 1.2-10 keV energy spectrum of the source can be approximated with an absorbed cutoff power-law model. We detect strong, luminosity-dependent emission lines in the 6-7 keV energy range. A narrow 6.42 keV line, observed in the sub-Eddington regime, is seen to evolve into a broad Fe-line profile in the super-Eddington regime. Other features are found at 6.67 and 6.97 keV in the Fe-line complex. An asymmetric broad-line profile, peaking at 6.67 keV, is possibly due to Doppler effects and gravitational redshift. The 1.2-79 keV broadband spectrum from Nuclear Spectroscopic Telescope Array (NuSTAR) and NICER observations at the outburst peak is well described by an absorbed cutoff power law plus multiple Gaussian lines and a blackbody component. Physical reflection models are also tested to probe the broad iron-line feature. Depending on the mass accretion rate, we found emission sites that are evolving from ∼5000 km to a range closer to the surface of the neutron star. Our findings are discussed in the framework of the accretion disk and its implication on the magnetic field, the presence of optically thick accretion curtain in the magnetosphere, jet emission, and the massive, ultrafast outflow expected at super-Eddington accretion rates. We do not detect any signatures of a cyclotron absorption line in the NICER or NuSTAR data. 
520 |a NASA (Grant HST-HF2-51440.001) 
546 |a en 
655 7 |a Article 
773 |t Astrophysical Journal