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GCN Circular 18811

Subject
LIGO/Virgo G211117: Gemini classification of 7 Pan-STARRS transients
Date
2016-01-03T21:29:22Z (9 years ago)
From
S. J. Smartt at Queens U Belfast <s.smartt@qub.ac.uk>
K. C. Chambers, (IfA, University of Hawaii), T.-W. Chen (MPE), S. Smartt 
K. Smith, D. Wright, (Queen���s University Belfast), M. E. Huber, A. S. B. Schultz (IfA),
M. Coughlin (Harvard), L. Denneau, H. Flewelling, A. Heinze, R. Kotak (QUB),
E. A. Magnier, N. Primak, A. Rest (STScI),  A. Sherstyuk (IfA), B. Stalder (IfA),
C. W. Stubbs (Harvard), J. Tonry, C. Waters (IfA),  D. Young (QUB)

Further to GCN 18786, we report spectroscopic classification of 7
of the Pan-STARRS transients within the northern localisation region
of G211117. Spectra were taken with GMOS on the Gemini North 8m
telescope (program GN-2015B-Q-4, PI. K. Chambers), with the R150
grating, filter GG455, and 1 arcsec slit giving useful wavelength
coverage 5000-9600 Angs. Typical exposure times were 600s, and the
spectra are of high quality (S/N 20-100). The data were taken on
the nights of 2015-12-30 and 2015-12-31 (with the MJDs of the
exposures given in parentheses below)

PS15dpn (57387.23)
Has a very blue continuum, with three weak (but real) emission line
features. These are tentatively identified as He I 5015.68, 5875.60
and H-alpha at z=0.175, although this is by no means certain as
two of them coincide with the strong telluric absorptions. The
transient was discovered on our first scan of the region on
2015-12-28 and is still rising, slowly (0.6 mag in 4 days, now
at i=19.9). This is an unusual spectrum and further
multi-wavelength observations are encouraged. Further spectra
are planned by our team.

PS15dow (57387.21): type Ib  (z=0.05 +/- 0.01) at +9 (SN1999ex) to +30d
(SN2008D) after maximum light. Therefore, explosion at least 20-40d 
before the GW trigger

PS15dpc (57387.26): type II z=0.056, +15-25d after explosion.
Therefore explosion 10-29d before the GW trigger.

PS15dpl (57387.40): type  Ia (z=0.03 +0.05/-0.015), at -8 to -11d before
peak. Assuming 17+/-1 days for rise time of type Ia SNe, this suggests
explosion 2015-12-21 to 2015-12-26. Which brackets the GW detection,
within the uncertainties. However as an apparently normal SN Ia, it
would appear unrelated.

PS15dot (57386.30) : type II at z=0.149 (host galaxy redshift). The
epoch is uncertain, but likely to be 10 to 20days after explosion.
This is a bright type II at M_i ~ -18.5, but likely to have exploded 10
days before the GW detection.

PS15dov (57386.32) : type II in UGC2836 (z=0.016702 host redshift). Fairly old
and reddened type II, with prominent P-Cygni lines of H-alpha and
Ca II. Likely more than 50 days old. Only 4-5 arcsec separation
from the recorded coordinates (NED and CBET) for SN203ih and SN2001I.
Exploded long before the GW trigger.

PS15dpb (57386.43) :  type II in UGC2828 (z=0.041045 host redshift).Fairly old
type II, around 20-30 days after explosion. Therefore, a likely
explosion epoch around 15-25d before G211117.
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