Multiband study of RX J0838-2827 and XMM J083850.4-282759: a new asynchronous magnetic cataclysmic variable and a candidate transitional millisecond pulsar

Journal
Date Issued
2017
Author(s)
Rea, N.
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Zelati, F. Coti
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Esposito, P.
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•
•
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Torres, D. F.
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•
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•
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Carrasco, L.
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Wieringa, M.
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Wilhelmi, E. De Oña
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Li, J.
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Bozzo, E.
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Ferrigno, C.
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Linares, M.
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Tauris, T. M.
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Hernanz, M.
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Ribas, I.
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Monelli, M.
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Borghese, A.
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Baglio, M. C.
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Casares, J.
DOI
Abstract
In a search for the counterpart to the Fermi-LAT source 3FGL J0838.8-2829, we performed a multiwavelength campaign: in the X-ray band with Swift and XMM-Newton; in the infrared and optical with OAGH, ESO-NTT and IAC80; and in the radio with ATCA observations. We also used archival hard X-ray data obtained by INTEGRAL. We report on three X-ray sources consistent with the position of the Fermi-LAT source. We confirm the identification of the brightest object, RX J0838-2827, as a magnetic cataclysmic variable that we recognize as an asynchronous system (not associated with the Fermi-LAT source). RX J0838-2827 is extremely variable in the X-ray and optical bands, and timing analysis reveals the presence of several periodicities modulating its X-ray and optical emission. The most evident modulations are interpreted as being caused by the binary system orbital period of ∼1.64 h and the white dwarf spin period of ∼1.47 h. A strong flux modulation at ∼15 h is observed at all energy bands, consistent with the beat frequency between spin and orbital periods. Optical spectra show prominent Hβ, He I and He II emission lines that are Doppler-modulated at the orbital period and at the beat period. Therefore, RX J0838-2827 accretes through a disc-less configuration and could be either a strongly asynchronous polar or a rare example of a pre-polar system on its way to reaching synchronism. Regarding the other two X-ray sources, XMM J083850.4-282759 showed a variable X-ray emission, with a powerful flare lasting for ∼600 s, similar to what is observed in transitional millisecond pulsars during the subluminous disc state: this observation possibly means that this source can be associated with the Fermi-LAT source.
Volume
471
Issue
3
Start page
2902
Uri
Url
Issn Identifier
0035-8711
Ads BibCode
2017MNRAS.471.2902R
Rights
open.access
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