Abstract

S. Mattila and P. Meikle, Imperial College, London; N. Walton, Institute of Astronomy, Cambridge; R. Greimel, Isaac Newton Group, La Palma; S. Ryder, Anglo-Australian Observatory; and C. Alard, DASGAL and Institut d'Astrophysique, Paris, report the discovery (7-sigma detection) of a possible supernova (mag 17.3) in an archival U.K. Infrared Telescope (UKIRT) K-band image obtained with IRCAM3 on 1998 Sept. 5.4 UT; images taken 3 min apart showed no detectable movement (seeing 0".8). The new object was located in the nuclear region of the starburst galaxy NGC 7714 at R.A. = 23h36m14s.0, Decl. = +2o09'24" (equinox 2000.0), which is 2" west and 5" north of (or 1 kpc from) the galaxy nucleus. The new object was apparent via image-subtraction techniques when compared with later K_s-band images obtained on 2001 Sept. 1.0 at the William Herschel Telescope (+ INGRID) and on 2000 Oct. 21 by A. Lancon and collaborators at the New Technology Telescope (+ SOFI), when no point source was visible at the location. Subtraction techniques reveal no object (limiting mag 18.5) at this location on a UKIRT H-band image obtained on 1998 Sept. 5 (NTT reference image). If this was a normal core-collapse supernova at any epoch, or a slow decliner (Mattila and Meikle 2001, MNRAS 324, 325) at an early epoch, an estimate of the H-K color limit implies an A_V towards the supernova of at least 6 mag. Alternatively, such a red H-K color could be produced by a slow-decliner type (e.g., SN 1998S) at a late phase with a much lower A_V. The search of archives for other detections of this possible supernova is encouraged.