According to IAUC 7335, the discovery was made on the image taken at Dec. 17.22, when the new object was mag 16.0. On the next day, it was confirmed by the KAIT image at mag about 15.5. It is probably in the rising phase. The posision of SN is: R.A. = 12h21m57s.02, Decl. = +4o27'45".6 (2000.0), which is about 32" east and 40" south of the nucleus of the face-on spiral galaxy M61. SN is superimposed on the bright arm, and on the location there is somewhat dim condensation on DSS image. There are a lot of condensations in the arms.
The type of SN 1999gn has been determined as type II by K. Ayani and H. Yamaoka from a wide-band spectrum (range 400-800 nm, resolution 0.6 nm) obtained with the Bisei Astronomical Observatory (BAO) 1.01-m telescope. It exhibits a blue continuum with a broad P-Cyg H-alpha profile and H-beta absorption. The expansion velocity of the supernova was derived to be 5,300 km/s [vsnet-alert 3842].
This supernova peaked at about mag 14 in late December 1999; measurements were given at about 14.9 on December 20, 1999 and 13.4 on December 25, 1999, 16.0 on January 1, 2000.
Last Modification: February 18, 2009