Optical Studies of 15 Hard X-ray Selected Cataclysmic Binaries

TL;DR

This study uses optical spectroscopy and photometry to analyze 15 hard X-ray selected cataclysmic binaries, discovering new systems, pulsations, and orbital periods, revealing the magnetic nature of these binaries and favoring intermediate polars.

Contribution

It provides new optical identifications, detects pulsations, and measures orbital periods, enhancing understanding of magnetic CVs selected via hard X-ray surveys.

Findings

Detection of coherent pulsations in three systems, confirming their intermediate polar nature.

Discovery of two new eclipsing systems with specific orbital periods.

Identification of a long 4.637-day orbit and a 12.76-hour orbital period, supporting the prevalence of magnetic CVs.

Abstract

We conducted time-resolved optical spectroscopy and/or time-series photometry of 15 cataclysmic binaries that were discovered in hard X-ray surveys by the Swift Burst Alert Telescope (BAT) and the International Gamma-Ray Astrophysics Laboratory (INTEGRAL), with the goal of measuring their orbital periods and searching for spin periods. Four of the objects in this study are new optical identifications: Swift J0535.2+2830, Swift J2006.4+3645, IGR J21095+4322, and Swift J2116.5+5336. Coherent pulsations are detected from three objects for the first time, Swift J0535.2+2830 (1523 s), 2PBC J1911.4+1412 (747 s), and 1SWXRT J230642.7+550817 (464 s), indicating that they are intermediate polars (IPs). We find two new eclipsing systems in time-series photometry: 2PBC J0658.0-1746, a polar with a period of 2.38 hr, and Swift J2116.5+5336, a disk system that has an eclipse period of 6.56 hr. Exact or approximate spectroscopic orbital periods are found for six additional targets. Of note is the long 4.637-day orbit for Swift J0623.9-0939, which is revealed by the radial velocities of the photospheric absorption lines of the secondary star. We also discover a 12.76 hr orbital period for RX J2015.6+3711, which confirms that the previously detected 2.00 hr X-ray period from this star is the spin period of an IP, as inferred by Coti Zelati et al. These results support the conclusion that hard X-ray selection favors magnetic CVs, with IPs outnumbering polars.