TITLE:   GCN CIRCULAR
NUMBER:  15883
SUBJECT: iPTF14yb: iPTF Discovery of an Optical Afterglow-like Transient
DATE:    14/02/26 21:40:35 GMT
FROM:    S. Bradley Cenko at NASA/GSFC  <brad.cenko@nasa.gov>

S. B. Cenko (NASA/GSFC), M. M. Kasliwal (OCIW/Princeton), D. A. Perley (Caltech), D. Jewitt (UCLA), M. Ishiguro (Seoul National University), A. V. Filippenko (UC Berkeley), A. Horesh (Weizmann Institute), A. De Cia (Weizmann Institute), A. Rubin (Weizmann Institute), A. Gal-Yam (Weizmann Institute), O. Yaron (Weizmann Institute), I. Arcavi (LCOGT/KITP), Y. Cao (Caltech), and P. E. Nugent (LBNL/UCB) report on behalf of a larger collaboration:

As part of the ongoing Intermediate Palomar Transient Factory survey, we report the discovery of a new optical transient source, iPTF14yb, located at RA = 14:45:58.01, Dec: +14:59:35.4 (J2000.0).  In an image obtained at the Palomar 48-inch Oschin Schmidt telescope beginning at 10:18 UT on 2014 February 26, we measure an r-band magnitude of r = 18.42 +/- 0.05 mag.  In subsequent P48 imaging, the source faded rapidly, with a measured magnitude of r = 20.4 +/- 0.2 mag at 13:08 UT on 2014 February 26.  

Nothing was detected at this location (r > 20.5 mag) in an image obtained at 09:05 UT on 2014 February 26 (i.e., 1.2 hours prior to discovery).  A coaddition of previous (i)PTF imaging of this location from 2009-2012 with P48 reveals no sources at this location to a limit of r > 22.7 mag.

We obtained a target-of-opportunity spectrum with the Low Resolution Imaging Spectrometer (LRIS) mounted on the 10 m Keck 1 telescope beginning at 15:27 UT on 2014 February 26 (i.e., 5.2 hours after discovery).  Our spectrum covers the wavelength range from the atmospheric cutoff at ~ 3200 A to 10000 A.  Super-imposed on a relatively flat continuum, we detect a number of absorption features at a common redshift of z = 1.98 (preliminary wavelength calibration), including Mg II, Fe II, Mg I, and Ly-alpha.     

Given the rapid temporal evolution, the large distance and luminosity, and the observed spectrum, iPTF14yb resembles the optical afterglow of a gamma-ray burst.  We have triggered radio and X-ray observations to confirm this hypothesis, and encourage additional follow-up at all wavelengths (including archival searches of this location).

[GCN OPS NOTE(27feb14): Per author's request, MI was added to the author list.]