Abstract
We discovered Swope Supernova Survey 2017a (SSS17a) in the LIGO/Virgo Collaboration (LVC) localization volume of GW170817, the first detected binary neutron star (BNS) merger, only 10.9 hr after the trigger. No object was present at the location of SSS17a only a few days earlier, providing a qualitative spatial and temporal association with GW170817. Here, we quantify this association, finding that SSS17a is almost certainly the counterpart of GW170817, with the chance of a coincidence being ≤ 9 × 10-6 (90% confidence). We arrive at this conclusion by comparing the optical properties of SSS17a to other known astrophysical transients, finding that SSS17a fades and cools faster than any other observed transient. For instance, SSS17a fades >5 mag in g within 7 days of our first data point, while all other known transients of similar luminosity fade by <1 mag during the same time period. Its spectra are also unique, being mostly featureless, even as it cools. The rarity of "SSS17a-like" transients combined with the relatively small LVC localization volume and recent non-detection imply the extremely unlikely chance coincidence. We find that the volumetric rate of SSS17a-like transients is ≤ 1.6 × 104 Gpc-3 yr-1 and the Milky Way rate is ≤0.19 per century. A transient survey designed to discover similar events should be high cadence and observe in red filters. The LVC will likely detect substantially more BNS mergers than current optical surveys will independently discover SSS17a-like transients, however a 1 day cadence survey with the Large Synoptic Survey Telescope (LSST) could discover an order of magnitude more events.
| Original language | English (US) |
|---|---|
| Article number | L26 |
| Journal | Astrophysical Journal Letters |
| Volume | 848 |
| Issue number | 2 |
| DOIs | |
| State | Published - Oct 20 2017 |
Funding
This Letter includes data gathered with the 6.5 m Magellan Telescopes located at Las Campanas Observatory, Chile. This research has made use of the NASA/IPAC Extragalactic Database (NED) which is operated by the Jet Propulsion Laboratory, California Institute of Technology, under contract with the National Aeronautics and Space Administration. We thank the University of Copenhagen, DARK Cosmology Centre, and the Niels Bohr International Academy for hosting D.A.C., R.J.F., A.M.B., E.R., and M.R.S. during the discovery of GW170817/SSS17a. R.J.F., A.M.B., and E.R. were participating in the Kavli Summer Program in Astrophysics, “Astrophysics with gravitational wave detections.” This program was supported by the the Kavli Foundation, Danish National Research Foundation, the Niels Bohr International Academy, and the DARK Cosmology Centre. The UCSC group is supported in part by NSF grant AST– 1518052, the Gordon & Betty Moore Foundation, the Heising-Simons Foundation, generous donations from many individuals through a UCSC Giving Day grant, and from fellowships from the Alfred P. Sloan Foundation (R.J.F.), the David and Lucile Packard Foundation (R.J.F. and E.R.) and the Niels Bohr Professorship from the DNRF (E.R.). A.M.B. acknowledges support from a UCMEXUS-CONACYT Doctoral Fellowship. M.R.D. and B.J.S. were partially supported by NASA through Hubble Fellowship grant HST-HF-51348.001 and HST-HF-51373.001 awarded by the Space Telescope Science Institute, which is operated by the Association of Universities for Research in Astronomy, Inc., for NASA, under contract NAS5–26555. D.K. is supported in part by a Department of Energy (DOE) Early Career award DE-SC0008067, a DOE Office of Nuclear Physics award DE-SC0017616, and a DOE SciDAC award DE-SC0018297, and by the Director, Office of Energy Research, Office of High Energy and Nuclear Physics, Divisions of Nuclear Physics, of the U.S. Department of Energy under contract No. DE-AC02-05CH11231.
Keywords
- galaxies: individual (NGC 4993)
- stars: individual (SSS17a)
- stars: neutron
- supernovae: general
ASJC Scopus subject areas
- Astronomy and Astrophysics
- Space and Planetary Science