Paloma (RX J0524+42): the missing link in magnetic CV evolution?

Abstract

Decent optical photometry of the canditate magnetic CV Paloma has uncovered three persistent periods at 157, 146, and 136 min, which we interpret as the manifestation of the orbital motion of the system, the white dwarf's spin, and a related side-band frequency of the other two. All three periodicities are caused by a double-humped modulation of about 1 mag appearing only at certain fractions of the beat cycle, and it probably originates from one or two accretion spots. Our data is consistent with two plausible solutions, with the spin period being either 146 or 136 min. The appearance of a corresponding spin-folded light curve suggests two different scenarios, for which either pole switching between two diametrically opposed accretion regions (for P spin = 146 min) or pole migration of one single spot (with P spin = 136 min) is the preferred accretion mode. Complementary ROSAT X-ray observations and low-resolution spectroscopy provide supporting evidence of the magnetic nature of the object. Depending on the choice of the spin period, the degree of asynchronism with respect to the orbital period is 7% or 14%, implying a beat period of 0.7 or 1.4 days. Thus, the source populates the gap between the near-synchronous polars (<2%) and the DQ Herculis stars with long spin periods (e.g. EX Hya, V1025 Cen, DW Cnc). With an orbital period right within the period gap, Paloma is a key object for magnetic CV evolution: it might be the first bona fide transition object between the DQ Her and AM Her system with a white dwarf currently in the process of synchronisation.

X-Ray and Optical Study of the Gamma-ray Source 3FGL J0838.8–2829: Identification of a Candidate Millisecond Pulsar Binary and an Asynchronous Polar

“…The original group of four asynchronous polars have spin and orbit periods which periods differ by < ∼ 2% (Schwarz et al 2007, and references therein). In 1RXS J083842.1−282723, the difference we infer is 3.7%.…”

Paloma: A Magnetic Cv Between Polars and Intermediate Polars

“…However, powers of all other peaks were found to be more in the soft band compared to that in the hard band. We have folded the PN data using the ephemeris HJD0 = 2450897.35376 as given by Schwarz et al (2007). The folded X-ray light curves and HR curves corresponding to the derived orbital and spin periods are shown in Figure 3.…”

“…The galactic hydrogen column density (NH1) corrected flux (fX) was calculated by using the 'cflux' model. The X-ray luminosity of Paloma was calculated by assuming a distance of 240 pc (Schwarz et al 2007) in the energy band 0.3 − 10.0 keV and is given in Table 2.…”

“…There are two other systems namely RX J0524+42 (Paloma) and V697 Sco, which are described as nearly synchronous IPs, with P ω = (0.7 − 0.9) P Ω . Paloma also lies in the period gap and is thought to be currently in the process of attaining synchronism and evolving into a polar (Norton et al 2004;Schwarz et al 2007). The orbital period distribution of MCVs shows that the P Ω of polars are in the range of 1.0 − 10.0 hr, while a majority of the IPs have orbital periods longer than the period gap of 2 − 3 hrs (Scaringi et al 2010).…”

“…This object was first characterized by Schwarz et al (2007) using optical photometry and ROSAT X-ray observa-tions. They reported an orbital period of 157 minutes and two spin periods of 146 and 136 minutes.…”