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GCN Circular 25923

LIGO/Virgo S190930t: ATLAS Forced photometry of ZTF19acbpqlh (AT2019rpn)
2019-10-02T13:02:40Z (5 years ago)
Stephen Smartt at Queen's U/Belfast <>
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, M. Dobson, J. Gillanders, D.
O'Neil, P. Clark, S. Sim (QUB)

The transient ZTF19acbpqlh (AT2019rpn) was reported by Stein et al.
(GCN 25899) at r = 20.02 within the 95% localisation bayestar map (LVC
et al. GCN 25876).

ATLAS covered this region on 6 recent epochs, and forced PSF
photometry on the difference images at the position of this transient
gives the following 3-sigma limiting magnitudes and two 4-sigma detections. 

58752.21516 c < 18.24    
58754.21109 o < 18.71    
58755.35411 c < 21.00    
58756.60703339205 == s190930t discovery 
58756.2132  c < 19.47    
58757.23448 o 19.84 +/- 0.26
58758.21185 o 19.68 +/- 0.27

All mags are AB. 

c = cyan filter (a g+r composite)
o = orange filter (a i+r composite) 

Tan et al. (GCN 25916) reported r = 20.7 +/- 0.3 which could imply a
significant fade, although the uncertainty is significant. Our
measurements imply the transient is flat or slowly rising.

Karambelkar et al (GCN 25921) give a tentative identification of broad
H-alpha in their blue spectrum. Our ATLAS photometry would support
their conclusion of a young, relatively faint, type II SN. But further
data are required to confirm.
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