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Title: A DECam Search for an Optical Counterpart to the LIGO Gravitational Wave Event GW151226

We report the results of a Dark Energy Camera optical follow-up of the gravitational-wave (GW) event GW151226, discovered by the Advanced Laser Interferometer Gravitational-wave Observatory detectors. Our observations cover 28.8 deg(2) of the localization region in the i and z bands (containing 3% of the BAYESTAR localization probability), starting 10 hr after the event was announced and spanning four epochs at 2–24 days after the GW detection. We achieve $$5\sigma $$ point-source limiting magnitudes of $$i\approx 21.7$$ and $$z\approx 21.5$$, with a scatter of 0.4 mag, in our difference images. Given the two-day delay, we search this area for a rapidly declining optical counterpart with $$\gtrsim 3\sigma $$ significance steady decline between the first and final observations. We recover four sources that pass our selection criteria, of which three are cataloged active galactic nuclei. The fourth source is offset by 5.8 arcsec from the center of a galaxy at a distance of 187 Mpc, exhibits a rapid decline by 0.5 mag over 4 days, and has a red color of $$i-z\approx 0.3$$ mag. These properties could satisfy a set of cuts designed to identify kilonovae. However, this source was detected several times, starting 94 days prior to GW151226, in the Pan-STARRS Survey for Transients (dubbed as PS15cdi) and is therefore unrelated to the GW event. Given its long-term behavior, PS15cdi is likely a Type IIP supernova that transitioned out of its plateau phase during our observations, mimicking a kilonova-like behavior. We comment on the implications of this detection for contamination in future optical follow-up observations.
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Publication Date:
Report Number(s):
FERMILAB-PUB-16-218-AE-PPD; arXiv:1606.04538
Journal ID: ISSN 2041-8213; 1469400
Grant/Contract Number:
AC02-07CH11359; AC02-SF00515
Accepted Manuscript
Journal Name:
The Astrophysical Journal. Letters
Additional Journal Information:
Journal Volume: 826; Journal Issue: 2; Journal ID: ISSN 2041-8213
Institute of Physics (IOP)
Research Org:
Lawrence Berkeley National Lab. (LBNL), Berkeley, CA (United States); SLAC National Accelerator Lab., Menlo Park, CA (United States); Fermi National Accelerator Lab. (FNAL), Batavia, IL (United States)
Sponsoring Org:
USDOE Office of Science (SC), High Energy Physics (HEP) (SC-25)
Contributing Orgs:
DES Collaboration; The DES Collaboration
Country of Publication:
United States
79 ASTRONOMY AND ASTROPHYSICS; binaries: close; catalogs; gravitational waves; stars: neutron; surveys
OSTI Identifier:
Alternate Identifier(s):
OSTI ID: 1334270