SN1999gl – discovery

Tom Boles

SN1999gl in NGC 317B, discovered 1999 December 14. IAU Circular 7333 : G.M. Hurst, Basingstoke, England, reports the discovery by Tom Boles, Wellingborough, of a supernova (mag. 16.2) on unfiltered CCD images obtained in the course of the UK Nova/Supernova Patrol on Dec. 14.73 and 14.98 UT with a 0.36–m reflector. Boles measured the position of SN1999gl to be RA 0h 57m 40s.07, Dec +43º 47' 35".6 (equinox 2000.0; mean of two exposures). SN1999gl does not appear on an image obtained by Boles on Sept 17.02 (limiting mag about 18). M. Armstrong, Rolvenden, confirmed the presence of SN1999gl on Dec 14.976 and notes that it was not present on his own CCD image taken on Dec 4. The second Palomar Sky Survey does not show anything at the position of SN1999gl (limiting mag. about 20). Boles found the supernova to be at mag. 16.6 on Dec. 15.92. P. Garnavich, S. Jha, R. Kirshner, and P. Challis, Harvard–Smithsonian Center for Astrophysics, report that a spectrum of SN1999gl was obtained by P. Berlind with the Fred L. Whipple Observatory 1.5-m Tillinghast telescope on Dec. 16.1 UT, showing the supernova to be a type II event near maximum. Broad H-alpha and H-beta emissions, as well as He I 587.50nm, are evident in the spectrum. A deep Na I absorption line due to interstellar gas in the host galaxy has an equivalent width of 0.3 nm, implying that the supernova is heavily extinguished by dust. Strong, narrow emission lines from the host galaxy provide a redshift of 0.018.