{
  "bibcode": "2017GCN.20721....1G",
  "body": "A. Gal-Yam, G. Leloudas, P. Vreeswijk (Weizmann), K. C. Chambers\n(IfA), M. E. Huber (IfA), S. J. Smartt, K. W. Smith, D. Wright,\nD. Young (QUB), F. Taddia, C. Barbarino, A. Nyholm, C. Fremling,\nJ. Sollerman (OKC), M. T. Botticella (INAF-Capodimonte), M. Fraser\n(UCD), C. Inserra, E. Kankare, K. Maguire, M. Sullivan (Southampton),\nS. Valenti (UC Davis), O. Yaron, I. Manulis (Weizmann), E. Cappellaro\n(INAF-Padova),, M. Coughlin (Harvard), T.-W. Chen (MPE), L. Denneau,\nH. Flewelling, A. Heinze, T. Lowe, E. A. Magnier (IfA), A. Rest\n(STScI), B. Stalder, A. S. B. Schultz (IfA), C. W. Stubbs (Harvard)\nJ. Tonry, C. Waters, R. J. Wainscoat, H. Weiland, M. Willman (IfA) report:\n\n\nWe have reanalysed the spectrum of PS17bek obtained by PESSTO (Taddia\net al. GCN 20708), an object in the sky map of G274296.  The spectrum\nis blue but shows weak broad features and a weak emission line that\nwas previously identified with Halpha at z=0. The object was therefore\nthought to be Galactic.\n\nCross-correlating the spectrum with supernova template spectra in SNID\n(Blondin & Tonry, 2007), we find a good match to the spectra of\nsuper-luminous supernovae (SLSNe type I).  In particular, we find a\ngood match with the spectra of SN 2010gx at -5 days before peak if\nPS17bek is at a redshift of z~0.31. In this context, the weak emission\nline at 6559.4 is consistent with [O III] 5007 at z = 0.31, and we\nalso detect [O III] 4959 at a consistent redshift but lower\nsignificance. The [O III] lines are typically the strongest emission\nlines in SLSN dwarf, starforming hosts (Leloudas et al. 2015).  There\nis a faint, uncatalogued source in the Pan-STARRS1 3Pi r-band image\nwhich is likely the host at r~23.5 (Chambers et al. arXiv:1612.05560).\n\nWe therefore classify PS17bek as a SLSN I at z = 0.31. \nThe Pan-STARRS lightcurve is flat at i=19.8 over two days : \nMJD             mag     filter \n57802.30629\t19.85\ti\t\n57804.58218\t19.81\ti\n\nThis indicates that the object is likely close to maximum light\nand has a rest frame absolute magnitude of M_r ~ -21.0.\n\nAlthough these superluminous events are relatively rare by sky\ndensity, they have rise times from explosion to peak of around 20-40\ndays (e.g. Nicholl et al. 2015). Therefore the explosion probably\noccurred at least 20 days before the GW detection of G274296\n(57801.254 ; Shawhan et al. GCN20689) and is likely unrelated.",
  "circularId": 20721,
  "createdOn": 1487767863000,
  "email": "giorgos@dark-cosmology.dk",
  "subject": "LIGO/Virgo G274296:  PS17bek is a superluminous supernova at z=0.31",
  "submitter": "Giorgos Leloudas at Weizmann Institute of Science  <giorgos@dark-cosmology.dk>",
  "eventId": "LIGO/Virgo G274296"
}