Difference: GCNCIRCULAR21617 ( vs. 1)

K. C. Chambers (IfA), M. E. Huber (IfA),K. W. Smith (QUB), S. J. Smartt, (QUB), D. R. Young, M. Coughlin (Harvard), T.-W. Chen (MPE), J. Bulger, L. Denneau, H. Flewelling, A. Heinze, E. Kankare (QUB), T. Lowe, E. A. Magnier (IfA), A. Rest (STScI), B. Stalder (IfA), A. S. B. Schultz, C. W. Stubbs (Harvard) J. Tonry, C. Waters, R. J. Wainscoat, H. Weiland, M. Willman (IfA), D. E. Wright (QUB)

We report continued Pan-STARRS imaging of the transient SSS17a/DLT17ck in NGC4339 in filters i, z and y (see Chambers et al. GCN 21553 for more details of filters, photometry, methods etc).

Our reference stack and calibrations provide rapid reliable photometry with the host removed and we will continue to post updates while it is visible from Hawaii. A series of short exposures to avoid sky saturation in twilight in each of i, z, and y provide average nightly magnitudes (AB) of

MJD i err
57983.23 17.24 0.06
57984.24 17.91 0.05
57985.24 18.47 0.08

MJD z err
57983.23 17.26 0.06
57984.24 17.80 0.05
57985.24 18.31 0.06

MJD y err
57983.23 17.38 0.10
57984.24 17.59 0.07
57985.24 18.08 0.07

The decline rate 0.6 mag per day is still consistent with some of the kilonova models (Kasen et al. 2015, Barnes & Kasen 2013, Tanaka et al. 2014).

The very rapid decline (and weak high energy emission) may explain why transients of these types have not been recovered and recognised independently in ground-based wide-field surveys to date, before the LIGO-Virgo era.

For example at d=100Mpc, this transient would fade from around i=19.2 to 21.7 in four days in i-band (and would be fainter and faster in g, r and broad composite filters). Making it difficult to recover and recognise over multiple nights in "~10^3 deg per night" surveys such as PTF, Pan-STARRS, La Silla Quest, Skymapper, CRTS. And well beyond the wider, shallower, ASASSN and ATLAS sensitivities.

-- ShaonGhosh - 20 Aug 2017