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P.M. Garnavich, R.P. Kirshner, P. Challis (CfA), E. Michael, R. McCray (JILA), C.S.J. Pun, G. Sonneborn (NASA-GSFC), D. Branch (UOk), R. Chevalier (UVa), A.V. Filippenko (UCB), C. Fransson, P. Lundqvist (Stockholm Obs.), N. Panagia (STScI), M.M. Phillips (LCO), B. Schmidt (MSSSO), N.B. Suntzeff (CTIO), L. Wang, J.C. Wheeler (UTex), SINS Collaboration
We present HST images of a new unresolved source of emission near the inner circumstellar ring of SN~1987A. The brightening spot likely marks the onset of the collision between the SN~1987A ejecta and the dense gas in the circumstellar ring. The spot was first detectable in 1996 and has since increased in brightness by a factor of ten at wavelengths from the UV to the IR. In the F675W filter, the hotspot had a magnitude of 21.2 (STMAG system) in 1999 January. The source is at a position angle relative to the supernova of 29\circ and its angular distance from the supernova is 584±15 milliarcsec. This is projected slightly within the ring, 88%\ of the distance between the supernova and the peak ring flux at that position angle. The brightness increase has been exponential with an average rate in the optical of 2.2~millimag\;day-1\ from 1996.1 to 1999.3. The rise is faster than what is expected from elementary geometrical models of spherical or conical protrusions from the ring. Not one additional spot brighter than R\approx 23 has appeared in the three years since the detection of Spot~1 and we discuss possible explanations for this.
Support for this work was provided by NASA through grant number GO-08243 from the Space Telescope Science Institute, which is operated by the Association of Universities for Research in Astronomy, Inc., under NASA contract NAS5-26555.
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