An X-ray and Optical Study of the Dwarf Nova Candidate OGLE-BLG-DN-0064

Abstract

The source OGLE-BLG-DN-0064 (hereafter OGLE64) was classified as a potential dwarf nova based on its regular outburst activity revealed by the OGLE optical survey. In this paper we investigate the X-ray and optical emissions from the source OGLE64 based on archival Chandra and Swift X-ray data and our optical observations with the 6-m BTA telescope at the Special Astrophysical Observatory of the Russian Academy of Sciences. OGLE64 shows an X-ray luminosity \(L_{X}\approx 1.6\times 10^{32}\) erg s\({}^{-1}\) and a high X-ray-to-optical flux ratio \(F_{X}/F_{\textrm{opt}}\approx 1.5\) typical for accreting white dwarfs. The X-ray spectrum of OGLE64 is better fitted by the models of a power law with a photon index \(\Gamma\approx 1.9\) and an optically thin plasma with a temperature \(kT\approx 6.4\) keV. The optical spectrum shows hydrogen and neutral helium emission lines in some of which a double-peaked structure is observed. An analysis of the outburst activity of OGLE64 based on data from the OGLE, ZTF, ATLAS, and ASAS-SN optical surveys has revealed superoutbursts with a characteristic supercycle \(P_{\textrm{super}}\approx 400\) days. We found no significant variability in either the X-ray or optical light curves of OGLE64 that could be associated with the change in the visibility conditions for the emitting regions at different orbital phases. Our estimates of the orbital period of the system by indirect methods show that the period probably lies in the range \(P_{\textrm{orb}}\sim 1.5{-}3.5\) h. The properties of the X-ray and optical emissions from OGLE64 lead us to conclude that the system is an SU UMa-type dwarf nova.