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Discovery of a possible AGN ROTSE3 J115649.1+542726

ATel #1515; F. Yuan (U. Mich.), R. Quimby (Caltech), T. McKay, D. Chamarro, M. D. Sisson, C. Akerlof, (U. Mich.) and J. C. Wheeler (U. Texas) on behalf of the ROTSE collaboration
on 9 May 2008; 23:24 UT
Credential Certification: Fang Yuan (yuanfang@umich.edu)

Subjects: Optical, AGN, Transient

Referred to by ATel #: 1524, 1576, 1578, 1593, 1644, 3367

We report the discovery of an optical transient located at RA = 11:56:49.13 Dec = +54:27:25.7 (J2000, uncertainty <1"), in unfiltered CCD images taken by the 0.45m ROTSE-IIIb telescope at McDonald Observatory, Texas. The transient was detected at 18.1 ±0.1 mag on Apr 26.23 UT and observed to be around 17.8 mag from Apr 28. 21 UT to May 6.23 UT. The transient is near a group of galaxies at z=0.062 in SDSS images, but no counterpart is visible at its position. The closest SDSS source is a r=23.13 mag galaxy some 8" away. There are no known X-ray or radio sources cataloged in NED or SIMBAD at the location of the optical transient.

We observed the target nightly with the Palomar 60" telescope in the g, r, and i bands beginning on May 2. A slow brightening trend is noted in each band as summarized below:

# Date       g          r         i 
May 2.27 18.1 18.1 18.2
May 8.24 17.7 17.8 17.8

We obtained spectra of the target on two nights with the 9.2m Hobby-Eberly Telescope (+ Marcario Low-Resolution Spectrograph), and one night with the Palomar 200" telescope (+ Double Beam Spectrograph).

# Date     Instrument      Range            Observers                    
May 1.24 HET/LRS 420-890 nm S. Odewahn and V. Riley
May 2.29 P200/DBSP 320-900 nm B. Cenko
May 8.25 HET/LRS 420-890 nm S. Rostopchin and Amy Westfall

The data from the three nights all show a mostly featureless, blue continuum (approximately f_nu ~ nu0.35). There is a broad emission feature at 5650 A, which is seen in all three epochs.

Based on its lightcurve and spectra, we tentatively categorize it as a background AGN. If the broad emission feature seen in the spectra is attributed to the Mg II doublet, this would imply a redshift of z=1.02.

A finding chart of the object can be found at http:/www.rotse.net/rsvp/j115649.1+542726/j115649.1+542726.jpg