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GCN Circular 20437

Subject
LIGO/Virgo G268556: Gemini spectra of Pan-STARRS1 transients
Date
2017-01-12T10:27:29Z (7 years ago)
From
S. J. Smartt at Queens U Belfast <s.smartt@qub.ac.uk>
K. C. Chambers (IfA), T.-W. Chen (MPE), S. J. Smartt, (QUB),
M. E. Huber (IfA), K. W. Smith (QUB), D. R. Young, D. E. Wright (QUB),
M. Coughlin (Harvard), L. Denneau, H. Flewelling, A. Heinze,
E. A. Magnier (IfA), A. Rest (STScI), B. Stalder (IfA),
A. S. B. Schultz, C. W. Stubbs (Harvard) J. Tonry, C. Waters,
R. J. Wainscoat, H. Weiland (IfA)


Further to Chambers et al. GCN 20410, we report initial results of
spectroscopic classifications. We used Gemini-North + GMOS (R400
grating, 4491-8778 Angs) on MJD = 57761 (2017 Jan 08) to target
objects which had either evolving lightcurves (rising/falling) and/or
no obvious host galaxy. We report three classifications : 

PS17fj is a SN Ia at redshift = 0.239
PS17fl is most likely a SN Ib/Ic at or before peak at z=0.018
PS17fn is most likely a young type SN II at z=0.074 

Further details as follows  

PS17fj :
The best matches are SN1999ef +7d (normal-Ia), SN2001fe +6d
(normal-Ia). Reasonable fits are also found for the 91T-like SN2003fa
91T-like. With an absolute mag of -19.7 mag, this is brighter than
normal Ia, but typical for 91T-like. There is no host in SDSS, but the
deeper PS1 3Pi stack (Chambers et al. 2016 arXiv 16120.5560) , shows a
faint source at r~22.6 which is likely a dwarf galaxy host.  The
source is now fading.

PS17fl :
The spectrum has strong emission lines from the r=18.47 host galaxy,
giving the redshift of z=0.081. It is also close to the centre of the
compact host in the PS1 reference frames (0.7 arcsec) and the GMOS
spectrum is likely contaminated with continuum flux from the host as
it is not resolved in the 2D images. The spectrum has a blue
continuum, consistent with the host galaxy. If a galaxy continuum
(matched to the SDSS colours) is subtracted then reasonable fits to
the spectrum are found for a Ib or Ic SN at or before peak.  It is
possible it is still rising, as a fit to SN2005bf at -8days is
reasonable.  The distinct lack of Si II means a Ia is unlikely. It is
currently i = 20.17, or M_i ~ -17.7.


PS17fn : 
PS17fn shows a blue continumm and galaxy emission lines of H-alpha and [SII]
at z = 0.074. There is a broad and shallow emission profile at the
position of H-alpha. The spectrum is noisy below 5000Angs (restframe),
but is rising with a continuum blackbody temperature around 10,000K
There is no good match from either SNID and GELATO. It is likely a
very young type II, which is consistent with the lightcurve rise of
0.6mag in 3 days. The current mag of i=20.27 corresponds to an
absolute mag of M_i ~ -17.4.
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