TITLE:   GCN CIRCULAR
NUMBER:  21633
SUBJECT: LIGO/Virgo G298048: Pan-STARRS izy photometry of SSS17a/DLT17ck  
DATE:    17/08/21 16:03:52 GMT
FROM:    S. J. Smartt at Queens U Belfast  <s.smartt@qub.ac.uk>

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) as follows. 

Pan-STARRS is observing at lower altitude than it has ever done, Poor
conditions and airmass>3 hampered the fourth night of observing (57986
= 2017-08-21 UT).  The difference images showed faint flux in z band,
but no detection in i and y. The forced photometry in the z-band at
the position of the transient is reported. The quick estimates for i
and y need to be verified.

MJD             i       err 
57983.23	17.24	0.06
57984.24	17.91	0.05
57985.24	18.47	0.08
57986.24        <18.5   limit only    

MJD             z       err 
57983.23	17.26	0.06
57984.24	17.80	0.05
57985.24	18.31	0.06
57986.24        18.27   0.33 

MJD             y       err 
57983.23	17.38	0.10
57984.24	17.59	0.07
57985.24	18.08	0.07
57986.23        <18.0   limit only