PS15adk is a recurrent CV detected in ASASSN and CRTS
ATel #7418; S. J. Smartt, K. Smith, D. Wright, D. Young (QUB)
on 20 Apr 2015; 16:02 UT
Credential Certification: Stephen Smartt (s.smartt@qub.ac.uk)
Subjects: Cataclysmic Variable, Supernovae
In ATel #7407 (Wright et al.), we reported detection of the bright transient and possible supernova PS15adk at z=16.62 in PSST at coordinates RA=16:33:13.65, Dec=-12:45:35.0. This is actually the recurrent variable (a likely CV) which has been discovered previously by CRTS (SSSJ163313.6-124534 in CRTS DR2; see Drake et al. 2009, ApJ, 696, 870.) and ASASSN (ASASSN-14bi ; see Davis et al.. 2015, AAS Meeting 225,344).
ASASSN-14bi and CRTS record the position of the transient (the CV which has had
multiple outbursts) to be the same as the R=19.4 stellar source in the GSC2.3 catalogue
(S8NM005820 in Vizier).
However the Pan-STARRS position of the transient is approximately 1.8 arcseconds south east of the R=19.4
stellar source, and coincident with a fainter source at r=21.5 (from Pan-STARRS1 stacked images). The Pan-STARRS image resolves the two sources as separate objects and shows the PSST source is coincident with the
fainter object.
As expected, the CRTS coordinates (from CSDR2 http://nesssi.cacr.caltech.edu/DataRelease/ ) of the transient
object record the position of the star S8NM005820 when the CV is in quiescence, as CRTS does
not detect or resolve the fainter source. CRTS then measures the true position of the CV when in
outburst, which is the same as we measure in PSST.
Hence the coordinate discrepancy is simply due to a coincidence of two sources being within 2 arcsecs, and the
optical transient being a CV which originates from the fainter star (which is undetected
in CRTS and ASASSN) and is now visible in the Pan-STARRS images.
We thank Kris Stanek for pointing out the initial coincidence.
