SN1999bt – discovery

Tom Boles

SN1999bt was discovered by Tom on the second night out with his new 14-inch f/11 SCT and AP7 CCD. The discovery – his third supernova – was made on exposures taken on 1999 April 9.120 and 13.088 UT. The bright galaxy is IC 1254, but the supernova is probably associated with the much fainter anonymous galaxy to the south. Tom Boles’ account : My supernova discoveries usually happen in October. SN1997dn and SN1998eg were first imaged on the 29 and 19 October respectively. This one broke the pattern. I had spent the previous two weeks setting up my new system, which now consists of a C14 controlled by a Paramount robotic mount and coupled to an Apogee AP7 camera. The increased light grasp of the 14-inch over my 10-inch, and the back-illuminated SITe chip in the AP7, all helped to get deep enough to spot 1999bt. The supernova clocks in at v = 18.1, with a recession velocity of 14,960 km/s (as measured on the 1.5-m telescope at the Whipple Observatory). As far as I know, this is the second furthest supernova discovered by an amateur. The furthest was discovered earlier this year by Mike Schwartz: SN1999z, at 15,200 km/s. I was patrolling IC 1254, and indeed thought that SN1999bt was part of that galaxy. Careful inspection shows it to be part of an adjacent anonymous galaxy, which was confirmed by its redshift. Note that the bright area on the top left-hand corner of the image is flare from the 11th magnitude star GSC 4424 0081, which is just out of the field, and is not caused by not power-supply fogging, as sometimes happens with CCDs. Because my set-up was new, my earlier reference images were not good enough to confirm the suspect. I had to rely on the kind help of Mark Armstrong, who obtained a confirmation image and provided astrometry, and also on Mike Schwartz of Oregon, who provided one of his reference images.

IAU Circular 1398 : G.M. Hurst, Basingstoke, England, reports the discovery by T. Boles, Wellingborough, of an apparent supernova (mag about 17) on exposures taken with a 0.14-m f/11 (+ AP7 camera) for the UK Nova/Supernova Patrol on Apr. 9.120 and 13.088 UT. The new object is in the field of IC 1254 but is probably linked to a much fainter galaxy just south of the suspect. M. Armstrong, Rolvenden, has measured the following precise position from the discovery exposure of Apr. 9: RA 17h 11m 37s.77, Dec +72º 25' 15".5 (equinox 2000.0). Hurst notes that the new object does not appear on the Palomar Sky Survey (1953 June 15) or on the second generation sky survey images (epoch 1993.625) at the Space Telescope Science Institute website. S. Jha, P. Garnavich, P. Challis, and R. Kirshner, Harvard–Smithsonian Center for Astrophysics, report that a spectrum of SN1999bt was obtained by M. Calkins on Apr. 14.5 UT with the F.L. Whipple Observatory (FLWO) 1.5-m telescope (+ FAST spectrograph) and reveals it to be a type-Ia supernova, about two weeks past maximum light. Concurrent images taken at the FLWO 1.2-m telescope (+ 4Shooter) by L. Macri yield V = 18.1 for the supernova, which is located 4" west and 10" north of the host galaxy. Cross-correlation of the host-galaxy spectrum with an absorption-line template yields a recession velocity of 14,960 +/– 60 km.