{
  "bibcode": "2019GCN.25386....1S",
  "body": "S. Smartt (QUB), D. Malesani (DARK), K. W. Smith (QUB), M. Huber (IfA,\nUniv. of Hawaii), K. Chambers, A.  Schulz (IfA), D. R. Young,\nO. McBrien, J. Gillanders. S.  Srivastav, D. O'Neil, P. Clark, S. Sim\n(QUB), T. de Boer, J. Bulger, J. Fairlamb, M. Huber, C.-C. Lin,\nT. Lowe, E. Magnier, R. J.  Wainscoat, M. Willman (IfA, Univ. of\nHawaii), T.-W, Chen (MPE), A.  Rest (STScI), C. Stubbs (Harvard)\n\nIn the search of the skymap of the NSBH event S190814bv (The LIGO\nScientific Collaboration and the Virgo Collaboration, GCN 25333,\n25324) the DECam-GROWTH team identified DG19sevhc (AT2019npy; Andreoni\net al. GCN 25362) as a candidate. It was followed up by Rossi et al\n(GCN 25383) and Dichiara et al. (GCN 25374).  The latter reported an\nunusual and rapid z-band rise, which drew attention.\n\nWe found a previous source detection close to this position on\ndifference images taken during the Pan-STARRS Survey For Transients\n(Huber et al. 2015, ATel 7153) at i=20.9, on multiple images from\nMJD=58335 (2018-08-05).  However closer inspection revealed that the\nsource was not a transient.\n\nThere is a faint red star which is coincident with background extended\nflux (probably a faint, red galaxy) and the star appears to have slow\nproper motion. This produced a dipole source in the Pan-STARRS\ndifference images, and triggered a new source detection.  The motion\nbetween the Pan-STARRS reference and the image from MJD=58335 is\nvisually clear (about 1.4 arcsec).  \n\nWe further inspected the separate Pan-STARRS 3Pi epochs\n(Chambers et al. 2016, arXiv:1612.05560C). Using 3 images with\nreasonable S/N between 2010 September and 2014 August, plus the public\nDECam image from 2019 August, the position of the star traces a vector\ntowards the S-E. We estimate a proper motion of 0.07 and -0.12\narcsec/yr in RA and Dec, respectively.\n\nHence we conclude that AT2019npy is not a transient, but resulted\nfrom the proper motion of this star leaving a positive residual\nin the DECam images of 2019 August, and the DECam references. \nThe unusual spatial coincidence of the moving star and background galaxy \nmade the original DECam identification as a transient quite understandable and \nreasonable.",
  "circularId": 25386,
  "createdOn": 1566081905000,
  "email": "s.smartt@qub.ac.uk",
  "subject": "LIGO/Virgo S190814bv: Pan-STARRS imaging indicates DG19sevhc (AT2019npy) is a proper motion star",
  "submitter": "Stephen Smartt at Queen's U/Belfast  <s.smartt@qub.ac.uk>",
  "eventId": "LIGO/Virgo S190814bv"
}