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Multiple cyclotron line-forming regions in GX 301−2

Fürst, F. and Falkner, S. and Marcu-Cheatham, D. and Grefenstette, B. and Tomsick, J. and Pottschmidt, K. and Walton, D. J. and Natalucci, L. and Kretschmar, P. (2018) Multiple cyclotron line-forming regions in GX 301−2. Astronomy and Astrophysics, 620 . Art. No. A153. ISSN 0004-6361.

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We present two observations of the high-mass X-ray binary GX 301−2 with NuSTAR, taken at different orbital phases and different luminosities. We find that the continuum is well described by typical phenomenological models, like a very strongly absorbed NPEX model. However, for a statistically acceptable description of the hard X-ray spectrum we require two cyclotron resonant scattering features (CRSF), one at ∼35 keV and the other at ∼50 keV. Even though both features strongly overlap, the good resolution and sensitivity of NuSTAR allows us to disentangle them at ≥99.9% significance. This is the first time that two CRSFs have been seen in GX 301−2. We find that the CRSFs are very likely independently formed, as their energies are not harmonically related and, if the observed feature were due to a single line, the deviation from a Gaussian shape would be very large. We compare our results to archival Suzaku data and find that our model also provides a good fit to those data. We study the behavior of the continuum as well as the CRSF parameters as function of pulse phase in seven phase bins. We find that the energy of the 35 keV CRSF varies smoothly as a function of phase, between 30 and 38 keV. To explain this variation, we apply a simple model of the accretion column, taking into account the altitude of the line-forming region, the velocity of the in-falling material, and the resulting relativistic effects. We find that in this model the observed energy variation can be explained as being simply due to a variation of the projected velocity and beaming factor of the line-forming region towards us.

Item Type:Article
Related URLs:
URLURL TypeDescription Paper
Fürst, F.0000-0003-0388-0560
Falkner, S.0000-0001-5209-991X
Marcu-Cheatham, D.0000-0001-8061-611X
Grefenstette, B.0000-0002-1984-2932
Tomsick, J.0000-0001-5506-9855
Pottschmidt, K.0000-0002-4656-6881
Walton, D. J.0000-0001-5819-3552
Natalucci, L.0000-0002-6601-9543
Kretschmar, P.0000-0001-9840-2048
Additional Information:© ESO 2018. Received 19 October 2017 / Accepted 13 September 2018. We thank the referee for their helpful comments. This research has made use of the NuSTAR Data Analysis Software (NuSTARDAS) jointly developed by the ASI Science Data Center (ASDC, Italy) and the California Institute of Technology (USA). We would like to thank John E. Davis for the slxfig module, which was used to produce all figures in this work. The Swift/BAT transient monitor results were provided by the Swift/BAT team. This research has made use of data obtained from the Suzaku satellite, a collaborative mission between the space agencies of Japan (JAXA) and the USA (NASA). L.N. acknowledges support by ASI/INAF grant I/037/12/0 and PRIN-INAF 2014 grant “Towards a unified picture of accretion in High Mass X-Ray Binaries”.
Group:NuSTAR, Space Radiation Laboratory
Funding AgencyGrant Number
Agenzia Spaziale Italiana (ASI)I/037/12/0
Istituto Nazionale di Astrofisica (INAF)PRIN-INAF 2014
Subject Keywords:accretion, accretion disks / magnetic fields / X-rays: binaries / stars: neutron / pulsars: individual: GX 301-2
Record Number:CaltechAUTHORS:20190102-155139776
Persistent URL:
Official Citation:Multiple cyclotron line-forming regions in GX 301−2 F. Fürst, S. Falkner, D. Marcu-Cheatham, B. Grefenstette, J. Tomsick, K. Pottschmidt, D. J. Walton, L. Natalucci and P. Kretschmar A&A, 620 (2018) A153 DOI:
Usage Policy:No commercial reproduction, distribution, display or performance rights in this work are provided.
ID Code:92017
Deposited By: George Porter
Deposited On:03 Jan 2019 20:54
Last Modified:17 Dec 2019 21:37

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