1 Introduction

Type Ia supernovae (SNe Ia) are considered to be the most reliable distance indicators on extragalactic, even cosmological distance scales (e.g. Gibson et al. 2000; Parodi et al. 2000; Perlmutter et al. 1995; Riess et al. 1998; Hamuy et al. 1996b and references therein). This is mainly based on their exceptional brightness and homogeneity, despite of the existence of "peculiar'' SNe Ia, such as SN 1991T or SN 1991bg (e.g. Filippenko 1997). Although the frequency of these "standard bombs'' (Jha et al. 1999) is low, regular monitoring of numerous galaxies (e.g. by the Lick Observatory Supernova Search, the Nearby Galaxies Supernova Search, etc.) supplies more than a hundred type Ia SN events per year. The reliability of SN-based distances is increased by the number of bright, well-observed, nearby SNe Ia in host galaxies whose distances can also be determined by other methods, such as Cepheids (Saha et al. 1997; Gibson et al. 2000; Jha et al. 1999), Tully-Fisher relation, or surface brightness fluctuation (e.g. Riess et al. 1996).

In this paper we present an updated distance to the type 2 Seyfert galaxy NGC 6951 via the type Ia SN 2000E. This galaxy has received considerable attention recently, especially its active nucleus and circumnuclear star-forming ring (Boer & Schulz 1993; Barth et al. 1995; Elmegreen et al. 1999; Kohno et al. 1999; Perez et al. 1999). Its distance has been determined via Tully-Fisher relation by several groups. Bottinelli et al. (1984) gives $\mu_{\rm0} = 31.85$ mag for the true distance modulus (corresponding to 23.4 Mpc), while Tully (1988) lists 24.1 Mpc ( $\mu_{\rm0} = 31.91$ mag).

SN 2000E has occurred just outside the origin of the long, northern spiral arm, in a relatively low surface brightness region (Fig. 1). This SN was discovered by G. Valentini and coworkers (Valentini et al. 2000) on Jan. 26, 2000, and immediately announced to be a type Ia event by Turatto et al. (cf. IAUC 7351). They reported the appearance of Si II, Si III, S II, Ca II and Fe III, the usual ions characterizing type Ia SNe, and also the presence of Na D indicating considerable reddening. The occurrence of SN 2000E was particularly interesting, because it appeared just a few months after the maximum of the type II SN 1999el, the first SN observed in NGC 6951. SN 1999el was located closer to the bar-dominated central region, but definitely outside the circumnuclear regime where star-forming processes are most active (Perez et al. 1999).

The expected maximum brightness of SNe Ia at the distance of NGC 6951 (about 13.5 mag) indicates that SN 2000E offers a good chance to increase the sample of bright, well-observed SNe Ia. The comparison of distances determined via SNe Ia and other methods may result in the refinement of the distance measuring techniques and the cosmic distance scale itself. This is especially important in the case of SNe, because they are used to measuring cosmological distances, where other methods often do not work, and its technique relies on a relatively small number of local calibrator SNe.

In the following the new photometric and spectroscopic observations of SN 2000E are described then the results are presented and discussed.