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Register a new userRX J2115--5840: confirmation of a new near-synchronous polar
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Gavin Ramsay
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Following the suggestion of Schwope et al that the magnetic cataclysmic variable RX J2115-5840 maybe a near-synchronous polar, we obtained optical polarimetry of this system over a 2 week period. From a power spectrum of the circular polarimetry data we determine that the spin period of the white dwarf and the binary orbital period which differ by 1.2%. RX J2115-5840 is thus the fourth near synchronous polar and has the shortest spin-orbit beat period: 6.3 days. By folding the data on spin, beat and orbital periods we find evidence that the accretion stream is directed towards opposite magnetic poles as the stream precesses around the white dwarf on the spin-orbit beat period. The phasing requires that the accretion flow must be directed onto the same magnetic field line at all spin-orbit beat phases implying that at some phases the flow must follow a path around the white dwarf before accreting. This is difficult to reconcile with simple views of how the accretion stream attaches onto the magnetic field of the white dwarf.
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We report the first time-resolved photometric and spectroscopic optical observations of the X-ray source RX J2133.7+5107, identified in the ROSAT survey. A clear persistent optical light pulsation is discovered with fast photometry at a period of P_{omega} =(570.823 +/-0.013) s which we associate with the spin period of an accreting white dwarf. Radial velocity curves of the strong emission lines show modulation with a period of P_{Omega} =(7.193 +/- 0.016) hr, identified as the orbital period. These observations establish that the source is a member of the intermediate polar class (IPs) of magnetic cataclysmic variables. With only 4 IPs with longer orbital periods, RX J2133.7+5107 is among the widest systems. It is a unique IP with an orbital period in the middle of the so-called (6-10)hr IP gap and it shows a significant degree of asynchronism with a ratio P_{omega}/P_{Omega} of 0.02. When attributed to the motion of the white dwarf, the emission lines orbital modulation yields a mass function of f_m = (1.05 +/- 0.21) 10^{-2} Msun which, for a probable inclination i < 45 deg and a white dwarf mass M_{wd} = (0.6-1.0) Msun, corresponds to a secondary mass M_{s} > (0.27-0.37) Msun.
We report optical and X-ray observations of the high-field polar RXJ1007.5-2017 performed between 1990 and 2012. It has an orbital period of 208.60 min determined from the ellipsoidal modulation of the secondary star in an extended low state. The spectral flux of the dM3- secondary star yields a distance of 790+-105 pc. At low accretion levels, RX{} exhibits pronounced cyclotron emission lines. The second and third harmonic fall in the optical regime and yield a field strength in the accretion spot of 94 MG. The source is highly variable on a year-to-year basis and was encountered at visual magnitudes between V sim 20 and V sim 16. In the intermediate state of 1992 and 2000, the soft X-ray luminosity exceeds the sum of the luminosities of the cyclotron source, the hard X-ray source, and the accretion stream by an order of magnitude. An X-ray high state, corresponding to the brightest optical level, has apparently not been observed so far.
We present the first optical polarimetric measurements of RX J1141.3-6410 which confirm that star as a polar. The circular polarization varies between 0 and 13% with the orbital period. Halpha spectroscopy shows that this line is formed by, at least, two components: a broad and a narrow one. The phase of maximum redshift of the broad component is shifted by 0.5 with the phase of maximum circular polarization which is not usual for this class of stars. We suggest a geometrical configuration for the system which could explain the main features of the polarimetric and spectroscopic data.
We present the first optical photometry of the counterpart to the candidate intermediate polar RX J0153.3+7446. This reveals an optical pulse period of 2333s +/- 5s. Reanalysis of the previously published ROSAT X-ray data reveals that the true X-ray pulse period is probably 1974s +/- 30s, rather than the 1414 s previously reported. Given that the previously noted orbital period of the system is 3.94 h, we are able to identify the X-ray pulse period with the white dwarf spin period and the optical pulse period with the rotation period of the white dwarf in the binary reference frame, as commonly seen in other intermediate polars. We thus confirm that RX J0153.3+7446 is indeed a typical intermediate polar.
Intermediate polars are members of the cataclysmic variable binary stars. They are characterized by a moderately magnetized white dwarf accreting matter from a cool main-sequence companion star. In many cases, this accretion gives rise to a detectable $X$-ray emission. VZ Sex is an interesting $X$-ray source whose nature needs a robust confirmation. Here, we used archive $XMM$-Newton observation to assign the source to the intermediate polar class. We applied the Lomb-Scargle periodogram method to detect any relevant periodic feature in the $0.1$--$10$ keV light curve and performed a spectral fitting of the $X$-ray spectrum in order to get information on the on-going accretion mechanism. By inspecting the periodogram, we detected a clear periodic feature at $simeq 20.3$ minutes that we interpret as the spin period of the white dwarf. We additionally found the typical side bands expected as the consequence of the beat between the spin and the orbital period of $simeq 3.581$ hours. The source is characterized by a unabsorbed flux of $simeq 2.98times 10^{-12}$ erg cm$^{-2}$ s$^{-1}$ corresponding to an intrinsic luminosity {of $simeq 7 times 10^{31}$ erg s$^{-1}$ } {for a distance of $simeq 433$ pc}. The existence of such features allow us to classify VZ Sex as a clear member of the intermediate polar class. Furthermore, with the estimated WD spin, the ratio $P_{spin}/P_{orb}$ is $simeq 0.09$, i.e. consistent with that expected for a typical IP system above the period gap. In addition, the estimated intrinsic luminosity opens the possibility that a bridge linking the normally bright IPs to the faint population of sources does exist.
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