TITLE:   GCN CIRCULAR
NUMBER:  27738
SUBJECT: GRB200514B: ATLAS detections of ZTF20aazpphd  
DATE:    20/05/14 20:36:48 GMT
FROM:    Stephen Smartt at Queen's U/Belfast  <s.smartt@qub.ac.uk>

S. J. Smartt, K. W. Smith (QUB), S. Srivastav, T.-W. Chen (MPE), D. R.
Young, M. Fulton, (QUB) L. Denneau, H. Flewelling, A. Heinze, J.
Tonry, H. Weiland (IfA, Univ. Hawaii), A. Rest (STScI), B. Stalder
(LSST), C. Stubbs (Harvard), O. McBrien, J. Gillanders, D.
O'Neil, P. Clark (QUB)

The transient ZTF20aazpphd (AT2020jww) was reported by Ahumada et al.
(GCN 27737) at r = 19.6 +/- 0.05 within the localization region of the
short GRB200514B (trigger 611140062) detected by the Gamma-Ray Burst
Monitor (GBM) on the Fermi satellite at MJD = 58983.38029 (GCN 27736).

ATLAS, the twin telescope system on Haleakala and Mauna Loa was
observing this region of sky in normal sky operations (Tonry et al.
2018, PASP, 130f4505, Smith et al. 2020, arXiv:2003.09052). We detect
ZTF20aazpphd before the ZTF epoch at the following magnitudes :

ATLAS c-band :
MJD         dt   m     err 
58983.42278 +1.02 19.47 0.13
58983.42461 +1.06 19.18 0.20
58983.43478 +1.31 19.46 0.13
58983.43890 +1.41 19.42 0.21

where dt is the time in hrs since Fermi trigger. 

ZTF reported the r-band : 
58983.49    +2.63 19.6  0.05 

The first ATLAS detection is 1.61hrs before the ZTF in the cyan-band
(a composite g+r filter). The two magnitudes are consistent, given the
errors and the different filter profiles. Therefore there is no
evidence of any rapid decline within this short interval, as might be
expected for a sGRB afterglow. We also have non-detections of
ZTF20aazpphd 2 days before, hence it is more likely a young supernova.