TITLE:   GCN CIRCULAR
NUMBER:  21590
SUBJECT: LIGO/Virgo G298048: Further Pan-STARRS izy photometry confirms rapid fading of SSS17a/DLT17ck in i and z bands 
DATE:    17/08/19 10:14:53 GMT
FROM:    S. J. Smartt at Queens U Belfast  <s.smartt@qub.ac.uk>

K. C. Chambers (IfA), S. J. Smartt, (QUB), M. E. Huber (IfA),
K. W. Smith (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

MJD             z       err 
57983.23	17.26	0.06
57984.24	17.80	0.05

MJD             y       err 
57983.23	17.38	0.10
57984.24	17.59	0.07

This confirms the fading seen in the DECam images (Nicholl et
al. GCN 21580), and is consistent with the other reports of fading (e.g. Yoshida et al. GCN
21586, Yang et al. 21579,  Arcavi et al. 21581).

The fading in i-band and bluer bands is clearly more pronounced than
in y-band and distinct from the rising NIR (Wiseman et al GCN 21584). 

This rate of fading is quantitatively similar to that of the kilonova
or merging NS models (Kasen et al. 2015, Barnes & Kasen 2013, Tanaka et
al. 2014). And is uncommon for the populations of known nearby
transients.