TITLE:   GCN CIRCULAR
NUMBER:  18848
SUBJECT: LIGO/Virgo G211117: iPTF Observations of PS15dpn
DATE:    16/01/09 14:26:51 GMT
FROM:    Brad Cenko at NASA/GSFC  <brad.cenko@nasa.gov>

S. B. Cenko (NASA/GSFC), M. M. Kasliwal (Caltech), L. P. Singer (NASA/GSFC), and V. Bhalerao (IUCAA) report on behalf of a larger collaboration:

We report here on P48 and Gemini observations of the transient PS15dpn (Chambers et al., GCN 18811).

PS15dpn was detected by the Palomar 48 inch telescope in R-band images obtained at 2:13 UT on 2015 December 28, with a magnitude of R = 20.8 +/- 0.2 mag.  The transient, internally dubbed iPTF15fgl, was not reported in our previous list of candidate counterparts (Cenko et al., GCN 18762) because of marginal evidence for excess flux at this location in a g-band image obtained on 2015 December 17.  Further analysis of these pre-trigger observations could not confirm this excess - thus we have no evidence for variability of this object prior to the LIGO trigger.

We obtained an optical spectrum of PS15dpn with the Gemini Multi-Object Spectrograph (GMOS) mounted on the 8 m Gemini North telescope beginning at 5:02 UT on 2016 January 6.  The source is (still) dominated by a blue continuum, with strong narrow emission lines corresponding to H-alpha and N II at a redshift of 0.174.  This is largely similar to the spectrum reported by Chambers et al. (GCN 18811), and we can confirm their tentative redshift of this source.  However, we do not see any evidence for He I lines in our spectrum.