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Keck Spectroscopy of Transients from the CRTS Survey

ATEL # 2654; S. G. Djorgovski, D. Stern, A. Drake, A. Mahabal, M. Graham, C. Donalek, R. Williams (Caltech), E. Beshore, S. Larson (UA/LPL), and E. Chistensen (Gemini)
on 30 May 2010; 2:14 UT
Password Certification: S. George Djorgovski (george@astro.caltech.edu)

Subjects: Optical, AGN, Cataclysmic Variables, Transients

We obtained long-slit spectra of several transients discovered by CRTS, using the LRIS instrument on the Keck-I telescope, on the nights of UT 2010 May 17 and 18, in good conditions.

CSS090826:223958+231837 reached a peak mag ~ 18 in an outburst in late October 2009, but has been undetected down to ~ 21 mag in most of the available CRTS data, and has a SDSS counterpart at ~ 22 mag. Our spectrum shows a blue continuum with narrow Balmer lines in emission at a ~ zero redshift. The source is notable as it exhibits a strong variability on ~ 10 - 15 min time scales, between the 4 exposures taken in a single night by the CSS survey. In that regard, it resembles CSS080924:233423+391423 (ATel #1741, ATel #1750). Thus, we interpret it as a probable (although unusually variable at short time scales) CV which has undergone a major outburst in October 2009.

CSS100408:073324+365005 (ATel #2652) is apparently associated with a radio source NVSS J073324+365004, a possible blazar, with a possible, marginal detection in SDSS at ~ 22 mag. It reached ~ 17.7 mag in an outburst in April 2010. The spectrum shows the host galaxy at z = 1.235 on the basis of an [O II] 3727 emission line and a corresponding 4000A break.

CSS100413:132854+174318 (ATel #2652) is associated with a radio source, and shows a standard QSO spectrum at z = 0.906. We thus classify it as a likely FSRQ.

CSS100504:215225+173437 (ATel #2652) is associated with a blazar CGRaBS J2152+1734. The spectrum shows a bright, featureless blue continuum, characteristic of blazars, but no significant features which would enable a redshift measurement.

CSS100507:164354-131525 was detected at ~ 15.5 mag on May 7, and has faded to ~ 16.5 mag by May 19, with no detections at all down to ~ 20 - 21 mag in all of the previously available CSS or DSS images. Our spectrum shows strong, broadened Balmer lines in absorption, superposed on a blue continuum. We interpret this as an extreme dwarf nova in an optically thick phase, reminiscent, e.g., of PQT 080119:091534+081356 (see ATel #1367).

We also obtained additional spectra of CSS100217:102913+404220 (see ATel #2544). The spectrum continues to evolve, with the Balmer lines getting weaker, and continuum slightly redder. Additional observations and data analysis are in progress.

More information and finding charts can be found at http://voeventnet.caltech.edu/feeds/ATEL/CRTS/

All CRTS SN discoveries are available from http://crts.caltech.edu/ and http://www.skyalert.org/

CRTS survey website


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