Peremennye Zvezdy (Variable Stars) 30, No. 2, 2010
Received 10 March; accepted 15 March.
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|Multiple outbursts of type Ia SNe in one galaxy present a unique opportunity to study the homogeneity of these objects. NGC 3147 is only the second known galaxy with three SNe Ia, another one is NGC 1316. We present CCD photometry for SN Ia 2008fv and compare the light and color curves of this object to those for SNe Ia discovered in NGC 3147 earlier: 1972H and 1997bq. The photometric properties of SNe 1997bq and 2008fv are nearly identical, while SN 1972H exhibits a faster-declining light curve.|
SN 2008fv was discovered by K. Itagaki on unfiltered CCD images exposed with a 0.6-m reflector around September 27.78 UT at magnitude 16.5. The new object was located at , (J2000.0), which is east and north of the center of the galaxy NGC 3147 (Nakano 2008).
Challis (2008), on behalf of the CfA Supernova Group, reported that a spectrum (range 350-880 nm) of SN 2008fv, obtained on September 30 with the MMT at Mt. Hopkins, showed it to be a normal type-Ia supernova about one week before maximum light. This is the fourth SN discovered in NGC 3147, the former were SN I 1972H (Goranskij 1972; Barbon et al. 1973), SN Ia 1997bq (Laurie and Challis 1997; Jha et al. 2006), and SN Ib 2006gi (Itagaki 2006; Elmhamdi et al. 2010).
We started photometric monitoring of SN 2008fv soon after its discovery, on October 3, with the remotely controlled telescope of the Tzec Maun Observatory. Later we also observed the SN with four other telescopes at three different locations. The data on the telescopes and detectors are presented in Table 1.
All image reductions and photometry were made using IRAF.1
The image of NGC 3147 obtained at C60 in the band is presented in Fig. 1. SN 2008fv and the sites of three previous SNe are marked, as well as the local standard stars. The magnitudes of these stars are reported in Table 2, they were calibrated on 12 photometric nights during monitoring SNe 2006gi and 2008fv. Stars 1 and 3 were also used as standards for the photometry of SN 2006gi (Elmhamdi et al. 2010).
SN 2008fv is projected on the spiral arm, and the subtraction of galaxy background is necessary for reliable photometry. The template images were constructed from frames obtained in November 2006 at C60 while monitoring SN 2006gi. After template subtraction, the magnitudes of the SN were derived by PSF fitting relative to a sequence of local standard stars.
|Maksutov-||35||133||SBIG ST-10E||Mayhill, New||TM35|
|Cassegrain||70||1050||Apogee AP-7p||Moscow, Russia||M70|
|Cassegrain||60||750||Apogee AP-47p||Nauchny, Crimea,||C60|
|Maksutov||50||200||Meade Pictor||Nauchny, Crimea,||C50|
Fig. 1. SN 2008fv in NGC 3147. Circles indicate the sites of previous SNe, the local standard stars are marked.
The observations of SN 2008fv at TM35 in the filters are presented in Table 3, and the photometry in the filters obtained with other telescopes is reported in Table 4.
|JD 2454000+||JD 2454000+|
The light curves are shown in Fig. 2. The maximum phase in the and bands is well-sampled by the observations, and we can derive the dates and magnitudes of maximum light: on JD 2454752, on the same date. The rate of early decline in the band corresponds to . From the list of type Ia SNe presented by Hicken et al. (2009), we select three SNe with similar and best-observed light curves: 1992bc, 2006ax, 2007af (Hamuy et al. 1996; Hicken et al. 2009). We fit the light curves of SN 2008fv to those for the three SNe listed above and find that, in the band, the fits for all the three objects are equally good. In the band, SN 1992bc provides the best fit, while in the band, SN 2006ax gives the best result. The -band light curve cannot be fitted well by any of these SNe, but SN 2006ax provides a slightly better match.