XMM-Newton observations of eleven intermediate polars and possible candidates

Aims. We aim to identify new intermediate polars (IPs) in XMM-Newton observations from a list of promising candidates. By selecting targets not previously known to be X-ray bright, we aim to uncover evidence for an X-ray underluminous IP subpopulation.Methods. We performed period searches on the XMM-Newton X-ray and optical data of our targets to seek both the spin and orbital periods, which differ in IPs. We also investigated the X-ray spectra to find the hot plasma emission shown by these objects. With archival Swift data we coarsely investigated the long-term X-ray variability, and with archival optical data from a variety of catalogues, we compared the optical to X-ray luminosity to identify X-ray faint objects. This paper presents the first XMM-Newton observation of the prototype IP, DQ Her.Results. We find firm evidence for HZ Pup, V349 Aqr, and IGR J18151-1052 being IPs, with likely white dwarf spin periods of 1552, 390, and 390 s, respectively. the former two have luminosities typical of IPs, and the latter is strongly absorbed and with unknown distance. GI Mon and V1084 Her are apparently non-magnetic CVs with interesting short-term variability unrelated to WD spin. V533 Her is probably a magnetic CV and remains a good IP candidate, while V1039 Cen is possibly a polar. the remaining candidates were too faint to allow for any firm conclusions.
German DLR [50 OR 1405, 50 OR 1711, 50 OR 1814]; TUBITAK 2214-A International Doctoral Research Fellowship ProgrammeTurkiye Bilimsel ve Teknolojik Arastirma Kurumu (TUBITAK); TUBITAKTurkiye Bilimsel ve Teknolojik Arastirma Kurumu (TUBITAK) [16BT100-1027]; Robert Martin Ayers Sciences Fund; ARC LIEF grant from the Australian Research Council,Australian Research Council [LE130100104]; Astronomy Australia Limited (AAL); Australian Government through the Commonwealth's Education Investment Fund (EIF); Australian Government through the National Collaborative Research Infrastructure Strategy (NCRIS)Australian GovernmentDepartment of Industry, Innovation and Science; National eResearch Collaboration Tools and Resources (NeCTAR); Australian National Data Service Projects (ANDS)
This work was supported by the German DLR under contracts 50 OR 1405, 50 OR 1711, and 50 OR 1814. Samet Ok is supported by TUBITAK 2214-A International Doctoral Research Fellowship Programme. We thank TUBITAK for a partial support in using the T100 telescope with project number 16BT100-1027. We acknowledge with thanks the variable and comparison star observations from the AAVSO International Database contributed by observers worldwide and used in this research. Many of the AAVSO observations were the result of Centre for Backyard Astronomy (CBA) campaigns. This research has made use of the APASS database, located at the AAVSO web site. Funding for APASS has been provided by the Robert Martin Ayers Sciences Fund. This work has made use of Astropy (Astropy Collaboration 2013, 2018). This research has made use of data, software and/or web tools obtained from the High Energy Astrophysics Science Archive Research Center (HEASARC), a service of the Astrophysics Science Division at NASA/GSFC and of the Smithsonian Astrophysical Observatory's High Energy Astrophysics Division. the national facility capability for SkyMapper has been funded through ARC LIEF grant LE130100104 from the Australian Research Council, awarded to the University of Sydney, the Australian National University, Swinburne University of Technology, the University of Queensland, the University of Western Australia, the University of Melbourne, Curtin University of Technology, Monash University and the Australian Astronomical Observatory. SkyMapper is owned and operated by the Australian National University's Research School of Astronomy and Astrophysics. the survey data were processed and provided by the SkyMapper Team at ANU. the SkyMapper node of the All-Sky Virtual Observatory (ASVO) is hosted at the National Computational Infrastructure (NCI). Development and support the SkyMapper node of the ASVO has been funded in part by Astronomy Australia Limited (AAL) and the Australian Government through the Commonwealth's Education Investment Fund (EIF) and National Collaborative Research Infrastructure Strategy (NCRIS), particularly the National eResearch Collaboration Tools and Resources (NeCTAR) and the Australian National Data Service Projects (ANDS). We are grateful to the anonymous referee, whose comments led to large improvements in the clarity of the paper.