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GCN Circular 18572

LIGO/Virgo G194575: La Silla QUEST, Pan-STARRS and PESSTO observations of iPTF15dld
2015-11-10T09:32:39Z (9 years ago)
S. J. Smartt at Queens U Belfast <>
D. Rabinowitz, C. Baltay, N. Ellman, E. Woodward (Yale), P. Nugent (LBNL)
S. J. Smartt, K. W. Smith, D. Wright D. Young,(Queen���s University Belfast),  
K. Chambers, M. Huber, E. Magnier, H. Flewelling, C. Waters, J. Tonry,
A. Schultz, N. Primak, A. Heinze, B. Stalder, L. Denneau, A. Sherstyuk (IfA Hawaii),
C. Stubbs, M. Coughlin (Harvard), A. Rest (STScI), M. Dennefeld (IAP),
J. Harmanen S. Mattila (Turku), L. Galbany (U de Chile), C. Inserra (QUB),
E. Kankare (QUB), K. Maguire (QUB),  M. Sullivan (Southampton),
S. Valenti (LCOGT), O. Yaron (Weizmann)

We report independent La Silla-QUEST and Pan-STARRS observations of 
iPTF15dld as reported by Singer et al. (GCN18497), and the follow-up 
observations of  Benetti et al. (GCN18563). Benetti et al. reported that this 
object was a broad lined type Ic SN. 

La Silla QUEST  operates the 10-sq-deg QUEST camera on the 1.0m 
ESO Schmidt at La Silla (Baltay et al. 2013), and feeds targets to the 
PESSTO spectroscopy programme (Smartt et al. 2015). As part of
routine surveying, a region of G194575 localisation area at
RA~1hr was scanned in the weeks before the trigger and targets
were ingested into the PESSTO marshall.  The object LSQ15bfp was 
discovered on 2015-10-05 at V=19.5 and is the same object as iPTF15dld.
An LSQ pre-discovery detection is visible on 2015-10-03 at V=20.2
It showed an early rising lightcurve of 0.7 mag in two days.  
Hence this object exploded 19 days before the trigger of 
G194575 (2015-10-22 13:33:19.942 UTC Singer et al. GCN18442).
LSQ has a non-detection of LSQ15bfp on 2015-09-08. 

The object was also detected by Pan-STARRS as PS15crl in 6 separate 
exposures on 2015 10 23.48 +/- 0.2 (UT),  +22hrs after the G194575 
trigger (see Smith et al. GCN 18484, Smartt et al. GCN 18445). 
PS15crl was measured at i=18.8 +/- 0.04, on each image with no 
significant intra-night variation. 

The reported coordinates of the object are :

LSQ coordinates of LSQ15bfp  : 00:58:13.27 -03:39:50.1
Pan-STARRS coordinates of PS15crl : 00:58:13.27 -03:39:50.2
iPTF coordinates of iPTF15dld :   00:58:13.28  -03:39:50.3

As in SDSS, the Pan-STARRS reference images show a very blue
host galaxy that is superimposed on a larger spiral. These are
probably distinct galaxies. 

Benetti et al.���s note that broad lined Ic SNe are relatively rare, and its 
location within the central 30% probability region make it an appealing 
target for further follow-up (see GCN18563). However the LSQ 
discovery date makes it unlikely to be related to G194575. 
Nevertheless PESSTO ( will take a number of 
spectra for follow-up (the first epoch was taken on 2015-11-08).
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