GCN Circular 20419
Subject
LIGO/Virgo G268556: Spectroscopic observations of ATLAS17aeu and iPTF17cw
Date
2017-01-10T16:58:02Z (8 years ago)
From
Mansi M. Kasliwal at Caltech <mansi@astro.caltech.edu>
T. Kupfer (Caltech), R. Quimby (SDSU), S. M. Adams (Caltech), H. Vedantham
(Caltech), M. M. Kasliwal (Caltech)
report on behalf of the GROWTH (Global Relay of Observatories Watching
Transients Happen) and iPTF (intermediate Palomar Transient Factory)
collaborations
We report the spectroscopic follow-up observations on ATLAS17aeu (Tonry et
al. LVC GCN #20382) and iPTF17cw (Kasliwal et al. LVC GCN #20398) using the
Double Beam spectrograph (DBSP) on the Palomar 200-inch telescope. The
position of both targets are within the probability contour of LIGO/Virgo
G268556 (LVC, GCN #20364). All observations were obtained on 2017 Jan 7 UT
under poor weather conditions with a partly cloudy sky. Classifications
were performed using Superfit (Howell et al. 2005, ApJ, 634, 1190).
ATLAS17aeu was observed on 2017-01-07.5 UT with a total exposure time of 60
min resulting in a signal to noise ratio ~1.5 in the continuum. No obvious
emission or absorption lines are detected in the spectrum. To search for
features from a Galactic source at z=0, we set a 3-sigma flux limit around
6563 Angstrom of 3.3e-17 ergs/s/cm^2/A. This result is consistent with
Chambers et al. (LVC GCN #20407) who reported a featureless spectrum of
ATLAS17aeu obtained with Gemini.
iPTF17cw was observed on 2017-01-07.55 with a total exposure time of 20 min
which results in a signal to noise ratio ~11 in the continuum. The spectrum
shows a blue continuum peaking around 3850 Angstroem (rest frame) with
weak, broad features. We found a good match of the spectrum with the
SNIc-BL SN1998bw pre-maximum at z=0.093. The redshift is consistent with
the photoz=0.101��0.0279 derived by SDSS for the host Galaxy.