CSS120330:154450-115323: A New Cataclysmic Variable Star Associated with the X-ray Source 1RXS J154449.5-115340

ATel #4160; R. M. Wagner (Ohio State U. and LBT Obs.); C. E. Woodward (U. Minnesota); K. L. Page and J. P. Osborne (U. Leicester); S. Starrfield (Arizona State U.); A. J. Drake, S. G. Djorgovski, and A. A. Mahabal (Caltech); J. Prieto (Princeton); E. Christensen, S. M. Larson, and E. Beshore (LPL/U. Arizona)
on 10 Jun 2012; 23:23 UT
Credential Certification: R. Mark Wagner (rmw@as.arizona.edu)

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On 2012 March 30 UT, the Catalina Real-Time Transient Survey (CRTS; Drake et al. 2009, ApJ, 696, 870) identified a highly variable optical source of 14.9 mag in data obtained by the Catalina Sky Survey (CSS) Schmidt telescope. The source designated CSS120330:154450-115323 varied irregularly between 16.3 and 14.9 mag between 2005 January 15 and the time of its recent identification. The position of CSS120330:154450-115323 is RA = 15:44:50.15, DEC = -11:53:22.6 (J2000). We obtained an optical spectrum (range 429.0-758.0 nm; resolution 0.67 nm) of CSS120330:154450-115323 on 2012 May 27.12 UT using the Steward Observatory Bok 2.3 m telescope (+B&C spectrograph) on Kitt Peak. CRTS photometry of CSS images obtained on the same night show the source at about 15.7 mag but with obvious short-timescale variability. The spectrum exhibits strong emission lines of hydrogen (H-alpha, H-beta, and H-gamma), He I (447.1, 501.5, 587.5, 667.8, and 706.5 nm), as well as absorption lines (Mg I 516.7-518.3 nm and Na I D 589.0 and 589.6 nm) of a K-type secondary star superposed on a red continuum. A much weaker broad emission line corresponding to He II 468.6 nm is also present. The presence of strong Balmer and weaker He I emission lines as well as the large H-beta to He II intensity ratio suggests that CSS120330:154450-115323 is a new dwarf nova cataclysmic variable star observed in quiescence. As noted previously by CRTS, the object lies close to the ROSAT X-ray source 1RXS J154449.5-115340. The position of CSS120330:154450-115323 is just consistent with the total 19 arcsec positional uncertainty of 1RXS J154449.5-115340 (Voges et al. 2000, IAUC 7432 ) lying at the edge of the error circle. To confirm the association of CSS120330:154450-115323 with 1RXS J154449.5-115340, we obtained a 1.1 ks ToO observation with Swift at the optical position on 2012 June 8.5 UT. We find an X-ray source located at RA = 15:44:50.20 and DEC = -11:53:23.1 (J2000) with an uncertainty of 2.8 arcsec. The X-ray source is coincident with CSS120330:154450-115323 within the errors. In the uvm2 filter (central wavelength of 224.6 nm) observed with the UVOT the source has a magnitude of 17.87 +/- 0.06. The Swift XRT count rate (0.3-10 keV) is 0.035 +/- 0.005 count s^-1. While the statistics are poor in the short observation, fitting the spectrum with an absorbed, optically thin component gives kT > 2.5 keV and N_H < 3.6e21 cm^-2. The source was detected previously with a ROSAT/PSPC count rate of about 0.049 +/- 0.012 counts s^-1 and an observed hardness ratio HR1 = 0.87 +/- 0.19. The Swift spectral parameters predict a ROSAT/PSPC equivalent count rate of about 0.037 counts s^-1 and thus comparable to that observed previously. The spectral parameters of the X-ray source are also consistent with the X-ray properties of dwarf novae in quiescence (Baskill, Wheatley, and Osborne 2005, MNRAS 357, 626). Further time resolved photometric observations of CSS120330:154450-115323 are required to determine the orbital period of the system as well as deeper X-ray observations to measure the detailed spectral properties in quiescence. We thank the Swift operations team and PI for their support.

CRTS light curve of CSS120330:154450-115323