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Discovery of a Luminous Supernova, PTF11dsf

ATel #3465; R. M. Quimby (Caltech), S. B. Cenko (Berkeley), O. Yaron, D. Xu (Weizmann Institute), A. Horesh (Caltech), J. Silverman, A. V. Filippenko, J. W. DeRose (Berkeley), P. Nugent (LBNL)
on 30 Jun 2011; 21:27 UT
Distributed as an Instant Email Notice Supernovae
Credential Certification: Robert Quimby (quimby@astro.as.utexas.edu)

Subjects: Optical, Ultra-Violet, X-ray, Supernovae, Transient

Referred to by ATel #: 3477

The Palomar Transient Factory (Law et al., 2009; Rau et al., 2009) 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 DeepSky 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.