Optical Identification of Four Hard X-ray Sources from the Swift All-Sky Survey

TL;DR

This study identifies four hard X-ray sources from the Swift survey using optical spectroscopy, revealing two as cataclysmic variables with accretion disks, and two as extragalactic objects, a Seyfert galaxy and a blazar, with supporting X-ray data.

Contribution

First optical identifications of four Swift X-ray sources, establishing their nature and providing combined optical and X-ray spectral analysis.

Findings

Two sources are cataclysmic variables with broad emission lines.

Detected orbital motion in one cataclysmic variable.

Two sources are extragalactic: a Seyfert 2 galaxy and a high-redshift blazar.

Abstract

We present the results of our optical identifications of four hard X-ray sources from the Swift all-sky survey. We obtained optical spectra for each of the program objects with the 6-m BTA telescope (Special Astrophysical Observatory, Russian Academy of Sciences, Nizhnii Arkhyz), which allowed their nature to be established. Two sources (SWIFT J2237.2+6324} and SWIFT J2341.0+7645) are shown to belong to the class of cataclysmic variables (suspected polars or intermediate polars). The measured emission line width turns out to be fairly large (FWHM ~ 15-25 A), suggesting the presence of extended, rapidly rotating (v~400-600 km/s) accretion disks in the systems. Apart from line broadening, we have detected a change in the positions of the line centroids for SWIFT J2341.0+7645, which is most likely attributable to the orbital motion of the white dwarf in the binary system. The other two program objects (SWIFT J0003.3+2737 and SWIFT J0113.8+2515) are extragalactic in origin: the first is a Seyfert 2 galaxy and the second is a blazar at redshift z=1.594. Apart from the optical spectra, we provide the X-ray spectra for all sources in the 0.6-10 keV energy band obtained from XRT/Swift data.