Discovery and redshift of an optical afterglow in 71 deg2: IPTF13bxl and GRB 130702A

Leo P. Singer, S. Bradley Cenko, Mansi M. Kasliwal, Daniel A. Perley, Eran O. Ofek, Duncan A. Brown, Peter E. Nugent, S. R. Kulkarni, Alessandra Corsi, Dale A. Frail, Eric Bellm, John Mulchaey, Iair Arcavi, Tom Barlow, Joshua S. Bloom, Yi Cao, Neil Gehrels, Assaf Horesh, Frank J. Masci, Julie McEneryArne Rau, Jason A. Surace, Ofer Yaron

Research output: Contribution to journalArticlepeer-review

46 Scopus citations


We report the discovery of the optical afterglow of the γ-ray burst (GRB) 130702A, identified upon searching 71 deg2 surrounding the Fermi Gamma-ray Burst Monitor (GBM) localization. Discovered and characterized by the intermediate Palomar Transient Factory, iPTF13bxl is the first afterglow discovered solely based on a GBM localization. Real-time image subtraction, machine learning, human vetting, and rapid response multi-wavelength follow-up enabled us to quickly narrow a list of 27,004 optical transient candidates to a single afterglow-like source. Detection of a new, fading X-ray source by Swift and a radio counterpart by CARMA and the Very Large Array confirmed the association between iPTF13bxl and GRB 130702A. Spectroscopy with the Magellan and Palomar 200 inch telescopes showed the afterglow to be at a redshift of z = 0.145, placing GRB 130702A among the lowest redshift GRBs detected to date. The prompt γ-ray energy release and afterglow luminosity are intermediate between typical cosmological GRBs and nearby sub-luminous events such as GRB 980425 and GRB 060218. The bright afterglow and emerging supernova offer an opportunity for extensive panchromatic follow-up. Our discovery of iPTF13bxl demonstrates the first observational proof-of-principle for ∼10 Fermi-iPTF localizations annually. Furthermore, it represents an important step toward overcoming the challenges inherent in uncovering faint optical counterparts to comparably localized gravitational wave events in the Advanced LIGO and Virgo era.

Original languageEnglish (US)
Article numberL34
JournalAstrophysical Journal Letters
Issue number2
StatePublished - Oct 20 2013


  • gamma-ray burst: individual (GRB 130702A)

ASJC Scopus subject areas

  • Astronomy and Astrophysics
  • Space and Planetary Science


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