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GK Persei and EX Hydrae: Intermediate polars with small magnetospheres

Suleimanov, V. and Doroshenko, V. and Ducci, L. and Zhukov, G. V. and Werner, K. (2016) GK Persei and EX Hydrae: Intermediate polars with small magnetospheres. Astronomy and Astrophysics, 591 . Art. No. A35. ISSN 0004-6361. https://resolver.caltech.edu/CaltechAUTHORS:20160404-142434779

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Abstract

Observed hard X-ray spectra of intermediate polars are determined mainly by the accretion flow velocity at the white dwarf surface, which is normally close to the free-fall velocity. This allows us to estimate the white dwarf masses as the white dwarf mass-radius relation M − R and the expected free-fall velocities at the surface are well known. This method is widely used. However, derived white dwarf masses M can be systematically underestimated because the accretion flow is stopped at, and re-accelerates from, the magnetospheric boundary R_m and, therefore, its velocity at the surface is lower than free fall. To avoid this problem, we computed a two-parameter set of model hard X-ray spectra, which allows us to constrain a degenerate M – R_m dependence. Previous works showed that power spectra of accreting X-ray pulsars and intermediate polars exhibit breaks at frequencies corresponding to Keplerian frequencies at the magnetospheric boundary. Therefore, the break frequency ν_b in an intermediate polar power spectrum gives another relation in the M – R_m plane. The intersection of the two dependences allows us, therefore, to determine the white dwarf mass and magnetospheric radius simultaneously. To verify the method, we analysed the archival Suzaku observation of EX Hya, obtaining M/M⊙ = 0.73 ± 0.06 and R_m/R = 2.6 ± 0.4, which is consistent with the values determined by other authors. Subsequently, we applied the same method to a recent NuSTAR observation of another intermediate polar GK Per performed during an outburst and found M/M⊙ = 0.86 ± 0.02 and R_m/R = 2.8 ± 0.2. The long duration observations of GK Per in quiescence performed by Swift/BAT and INTEGRAL observatories indicate increase of magnetosphere radius R_m at lower accretion rates.


Item Type:Article
Related URLs:
URLURL TypeDescription
https://doi.org/10.1051/0004-6361/201628301DOIArticle
http://arxiv.org/abs/1604.00232arXivDiscussion Paper
Alternate Title:GK Per and EX Hya: Intermediate polars with small magnetospheres
Additional Information:© 2016 ESO. Article published by EDP Sciences. Received 12 February 2016; Accepted 14 April 2016. Published online 07 June 2016. This work made use of data from the NuSTAR mission, a project led by the California Institute of Technology, managed by the Jet Propulsion Laboratory, and funded by the National Aeronautics and Space Administration. This paper is also based on data from observations with INTEGRAL, an ESA project with instruments and science data centre funded by ESA member states (especially the PI countries: Denmark, France, Germany, Italy, Spain, and Switzerland), Czech Republic and Poland, and with the participation of Russia and the USA. 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). V.S. thanks Deutsche Forschungsgemeinschaft (DFG) for financial support (grant WE 1312/48-1). V.D. and L.D. acknowledges support by the Bundesministerium für Wirtschaft und Technologie and the Deutsches Zentrum für Luft und Raumfahrt through the grant FKZ 50 OG 1602.
Group:NuSTAR
Funders:
Funding AgencyGrant Number
NASA/JPL/CaltechUNSPECIFIED
Deutsche Forschungsgemeinschaft (DFG)WE 1312/48-1
Bundesministerium für Wirtschaft und Technologie (BMWi)UNSPECIFIED
Deutsche Zentrum für Luft- und Raumfahrt (DLR)FKZ50OG1602
Subject Keywords:accretion, accretion disks – novae, cataclysmic variables – X-rays: binaries – methods: numerical
Record Number:CaltechAUTHORS:20160404-142434779
Persistent URL:https://resolver.caltech.edu/CaltechAUTHORS:20160404-142434779
Official Citation:GK Persei and EX Hydrae: Intermediate polars with small magnetospheres V. Suleimanov, V. Doroshenko, L. Ducci, G. V. Zhukov and K. Werner A&A, 591 (2016) A35 DOI: https://doi.org/10.1051/0004-6361/201628301
Usage Policy:No commercial reproduction, distribution, display or performance rights in this work are provided.
ID Code:65902
Collection:CaltechAUTHORS
Deposited By: Joy Painter
Deposited On:04 Apr 2016 22:58
Last Modified:03 Oct 2019 09:51

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