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Catalina limits for prior outbursts from GW170817 counterpart SSS17a

ATel #10856; A. J. Drake, S. G. Djorgovski, A. A. Mahabal, M. J. Graham (Caltech); E. Christensen, S. M. Larson (LPL/UA)
on 16 Oct 2017; 22:55 UT
Credential Certification: Andrew J. Drake (ajd@cacr.caltech.edu)

Subjects: Optical, Gravitational Waves, Neutron Star, Transient

The LIGO-Virgo collaboration recently announced the discovery of a GW event associated with a likely NS-NS merger (GW170817, Abbott et al. 2017, PRL, 119, 161101). A probable optical counterpart to the GW event (SSS17a, aka AT2017gfo) was identified by Coulter et al. (2017, GCN#21529).

Archival searches for prior optical outbursts of SSS17a have been reported based on LSQ (Rabinowitz and Baltay GCN#21599), ATLAS (Tonry et al. 2017, GCN#21886), SkyMapper (Moller, Chang and Wolf GCN#21542), and ASAS-SN (Cowperthwaite, Foley and Berger 2017, GCN#21533). Collectively, these authors find no evidence for prior outbursts in the period between 2013 and the discovery of SSS17a on 2017 August 17 UT.

We searched the Catalina Survey's archive for observations taken at the location of SSS17a, and identified 337 observations taken by the Siding Spring Survey between 2005 April 02 and 2013 July 01 UT. An additional 120 observations of the location were taken by the Catalina Schmidt between 2004 June 15 and 2016 May 09 UT. For each of the sets of images we produced a deep template by combining the observations. We then performed image subtraction on all of the images.

We find no clear evidence for a prior outburst at the location of SSS17a between 2004 and 2016 to V-mag limits varying from 18 to 19 (depending on observing conditions and telescope). However, since the data during this period is relatively sparse, we are unable rule out prior outbursts with timescales as short as the SSS17a event itself.