2011ATel.3465....1Q

The <a href='http://astro.caltech.edu/ptf/'>Palomar Transient Factory</a> (<a href='http://adsabs.harvard.edu/abs/2009PASP..121.1395L'>Law et al., 2009</a>; <a href='http://adsabs.harvard.edu/abs/2009PASP..121.1334R'>Rau et al., 2009</a>) reports the discovery of an optical transient, PTF11dsf. The

source is located at RA = 16:11:33.55, Dec. = +40:18:03.5 (J2000), which is offset from a faint (r∼22.6 mag) galaxy detected by the SDSS.

PTF11dsf was first detected with an R-band magnitude of about 19.8 on 2011 May 12 (UT). Follow-up observations with the Palomar 60" Telescope reveal the transient brightened further: it was about r=19.4

mag on June 27. PTF did not detect any previous outbursts from this source, which was observed on 30 nights between May 2009 and May 2011. A query of the <a href="http://supernova.lbl.gov/~nugent/deepsky.html">DeepSky</a> image

repository show that there was no previous outburst on 24 images taken

between June 2007 and July 2008.

Spectroscopic follow-up was performed with the Keck (+LRIS) and KPNO 4m (+RC Spectrograph) telescopes beginning June 2. The spectra show a blue continuum with narrow emission lines (including H, OII, and OIII) and absorption features from MgII and FeII, all at a common redshift of z=0.385. At this redshift, the peak optical luminosity is greater than -22 mag absolute. Broader components to the Hydrogen Balmer lines are evident in a Keck spectrum obtained on June 29, including a relatively strong H-gamma feature.

We requested Swift observations, which were carried out on June 3. Neglecting any contribution from the host galaxy, we measure the following preliminary UVOT magnitudes for the transient:

MJD Filter Mag Mag_err 55715.2812 U 18.46 0.21 55715.2578 UVW1 18.92 0.10 55715.2383 UVM2 18.78 0.06 55715.2773 UVW2 19.97 0.51

There was no source detected in the simultaneous XRT observation. We thank the Swift team for scheduling these ToO observations.