This is a picture of the SN in NGC 3627. The field of view in this R-band image is about 5 arcminutes on a side, and the position of SN 1997bs is marked with a box. North is to the left, east is down.
KAIT automatically detected this candidate during the night of April 14, 1997. It re-scheduled a confirmation image about 90 minutes later, which also shows the candidate. The next day, Chien Peng, a graduate student at UC Berkeley, noticed the candidate during his scan of the KAIT data and alerted the Berkeley team.
The object doesn't appear on some earlier images: compare pictures taken by KAIT on Apr 10 and Apr 13:
with pictures taken on Apr 15:
Based on these discovery images, the candidate is at
RA = 11:20:14.22 Dec = 12:58:19.4 (J2000)about 70 arcsec South and 10 arcsec W of the nucleus. It was about R=17 on UT 05:09 Apr 15, 1997.
The picture above shows five local comparison stars, marked with letters. Their magnitudes, taken from Wells et al., are:
U B V R I
A 13.66 13.72 13.17 12.83 12.50 Wells star 2, BBCRT star 5
B
C 16.70 16.53 15.94 15.61 15.20 Wells star 4
D 16.79 16.20 Wells star 3, BBCRT star f
Q 11.91 10.90 9.79 9.21 8.73 Wells star 1, BBCRT star 1
where Wells refers to a paper on SN 1989B, AJ 108, 2233 (1994);
see a link to the paper below, and BBCRT refers to a paper
on SN 1989B by Barbon et al., A&A 237, 79 (1990).
On April 16 UT, Alex Filippenko, Aaron Barth and A. M. Gilbert acquired a spectrum of the object with the Lick 3-m Shane reflector. The spectrum, range 3200-8000 Angstroms, resolution 7 Angstroms, shows that the object is a peculiar Type II supernova (formally known as Type IIn), dominated by relatively narrow (FWHM = 1000 km/s) Balmer emission lines on a featureless continuum. There are also many weaker Fe II emission lines.
Watch the supernova (slightly below and to the left of center) brighten and fade in this series of closeups of the field: Apr 10, Apr 15, Apr 22, Apr 26, May 3, May 20.
NGC 3627 is a galaxy about which we know quite a bit. It has hosted two previous SNe: SN 1973R and SN 1989B. You can read a nice paper about the Type Ia SN 1989B by Wells et al. in Astronomical Journal, vol 108, 2233 (1994).
NGC 3627 belongs to the Leo group of galaxies. There are several measurements of the distance to this group. Wells et al. (1994) states that Phillips says that Pierce measures a distance modulus of (m-M)=29.4 to NGC 3627 itself, via Tully-Fisher. Other distances to galaxies in the Leo group are:
who reference method distance mod ------------------------------------------------------------------------------ Harris et al. PASP, 102, 966 (1990) glob clusters 30.1 +/- 0.4 Ford et al. ApJ, 458, 455 (1996) PNLF 30.02 +/- 0.02 Sakai et al. ApJ, 478, 49 (1997) tip of RGB 30.3 +/- 0.2 Graham et al. ApJ, 477, 535 (1997) Cepheids 30.0 +/- 0.2 ------------------------------------------------------------------------------