CSS160603:162117+441254: pretending to be a contact system again.

ATel #9167; S. Zola (Jagiellonian University), S. Ciprini (ASDC Rome & INFN Perugia), B. Debski (JU), W. Ogloza, M. Drozdz (Mt. Suhora), F. Verrecchia (ASDC Rome & INAF-OAR), D. B. Caton (Appalachian State University), D. E. Reichart, J. P. Moore, A. P. LaCluyze, K. M. Ivarsen (University of North Carolina),E. de Miguel, T. Campbell, G. Roberts, M. J. Cook (CBA)
on 17 Jun 2016; 20:18 UT
Credential Certification: Staszek Zola (szola@oa.uj.edu.pl)

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An outburst in optical of the binary CSS160603:162117+441254 (also known as 2MASS J16211735+4412541, SDSS J162117.36+441254.0 and CRTS J162117.3+441254) was recently discovered by the Catalina survey (Drake et al., ATel#9112). Previously the shape of its light curve was attributed to a contact system (Palaversa et al., 2013, AJ, 146, 101, Lohr et al., 2013, A&A 549, 86, Drake et al., 2014, ApJS, 213, 9). Follow-up optical spectroscopy performed at the outburst revealed the presence of strong, double peaked Balmer and HeII emission lines that indicate the system to harbour an accretion disk and to be a cataclysmic binary (Scaringi et al. ATel#9122, Thorstensen ATel#9141, Szkody priv. communication) undergoing a transient accretion event. KWS pre-discovery observations indicate the system to be at outburst already on 2016-06-01.616 UT (Maehara, ATel#9113). We followed the system light curve evolution with two telescopes in Poland: 60cm at Mt. Suhora Observatory and 50cm at Krakow. Observations over the entire orbital period have been obtained on June 4,5,6,7,8 12 and 14. These taken on the first 5 nights show the system light curve to be typical of a cataclysmic binary, with a deep primary minimum and a shallow secondary one. The LC shape was quickly evolving: depth of the primary minimum was decreasing while that of the secondary one was increasing, likely in the viscous timescale (also reported by Zejda & Pejcha, ATel#9132). Data gathered on June 10th by CBA observers still exhibits a CV variable light curve properties. Observations taken on June 12 and 14 with the two Polish telescopes as well as on June 12 and 13 with the DSO-17 telescope, a part of the SKYNET robotic telescope network, revealed that the system returned to the pre-outburst quiescence state with its light curve back being similar to these of contact or Beta-Lyr type systems. No change in its shape can be noticed among the three nights but a difference in heights of the maxima is obvious. This so called O'Connell effect is usually explained as being due to magnetic activity, but it will have a different origin here. Furthermore, the deep minimum in the CV state has become a shallower one. A follow-up ToO Swift observation of CSS160603:162117+441254 with 2200s exposure was performed on June 14, 2016 already at the quiescence state. This represents the first observation by Swift of this object. Swift XRT data were taken in Photon Counting mode and did not reveal a detection of the target above the background in the 0.3-10keV band. On the other hand, Swift UVOT optical (V,U filters) and UV (W1, W2 filters, Poole et al. 2008, MNRAS, 383, 627) observations of CSS160603:162117+441254 were obtained in four slices per filter on the same pointing. Results are given here for the longer time slice (exposure duration about 150s) in observed magnitudes of the target: V=15.12+/-0.03, U=16.33+/-0.05, W1=17.00+/-0.09, W2=17.41+/-0.10. CSS160603:162117+441254 shows a striking similarity to HD 109962 exhibiting similar spectroscopic features and outburst occurring about once a year and lasting about 40 days (Walter & Bond, CBAT 370). However, duration of the current outburst in CSS160603:162117+441254 seems to be shorter and frequency of outbursts is unknown.