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Register a new userA new faint Type Ia Supernova: SN 1997cn in NGC 5490
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Observations of the recent SN 1991bg in the elliptical galaxy NGC 5490 show that this objects closely resembles, both photometrically and spectroscopically, the faint SNIa 1991bg. The two objects have similar light curves, which do not show secondary maxima in the near IR as normal type Ia supernovae. The host galaxy, NGC5490, lies in the Hubble flow. Adopting for SN1997cn a reddening E(B-V)=0, the absolute magnitude is faint: MV = -17.98 using Ho=65 and MV = -17.40 using Ho=85 km/(s Mpc). The latter value is in close agreement with the absolute magnitude of SN 1991bg on the SBF--PNLF--TF distance scale. The photospheric spectra of the two SNe show the same peculiarities, the deep TiII trough between 4000 and 4500A, the strong CaII IR triplet, the narrow absorption at about 5700A and the slow expansion velocity. In analogy to SN 1991bg the observed spectrum of SN1997cn has been successfully modeled by scaling down the W7 model by a factor of 2, assuming a rise time to B maximum of 18 days, a photospheric velocity and an effective temperature low compared to normal SNIa. The influence of the distance scale adopted on the input parameters of the best fit model is also discussed. These data demonstrate that peculiar SNIa like SN 1991bg are not once--in--a--lifetime events and that deep SN searches can be contaminated by underluminous SN Ia in a fairly large volume.
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Extensive and independent observations of Type Ia supernova (SN Ia) SN 2013dy are presented, including a larger set of $UBVRI$ photometry and optical spectra from a few days before the peak brightness to $sim$ 200 days after explosion, and ultraviolet (UV) photometry spanning from $t approx -10$ days to $t approx +15$ days referring to the $B$ band maximum. The peak brightness (i.e., $M_{rm B} = -19.65 pm 0.40$ mag, $L_{rm max} = [1.95 pm 0.55] times 10^{43}$ erg s$^{-1}$) and the mass of synthesised $^{56}$Ni (i.e., $M$($^{56}$Ni) = 0.90 $pm$ 0.26 M$_{odot}$) are calculated, and they conform to the expectation for a SN Ia with a slow decline rate (i.e., $Delta m_{15}(B)$ = 0.90 $pm$ 0.03 mag, Phillips 1993). However, the near infrared (NIR) brightness of this SN (i.e., $M_{rm H} = -17.33 pm 0.30$ mag) is at least 1.0 mag fainter than usual. Besides, spectroscopy classification reveals that SN 2013dy resides on the border of core normal and shallow silicon subclasses in the Branch et al. (2009) classification scheme, or on the border of the normal velocity SNe Ia and 91T/99aa-like events in the Wang et al. (2009a) system. These suggest that SN 2013dy is a slow-declining SN Ia located on the transitional region of nominal spectroscopic subclasses and might not be a typical normal sample of SNe Ia.
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We present extensive optical photometric and spectroscopic observations of the high-velocity (HV) Type Ia supernova (SN Ia) 2017fgc, covering the phase from $sim$ 12 d before to $sim 389$ d after maximum brightness. SN 2017fgc is similar to normal SNe Ia, with an absolute peak magnitude of $M_{rm max}^{B} approx$ $-19.32 pm 0.13$ mag and a post-peak decline of ${Delta}m_{15}(B)$ = $1.05 pm 0.07$ mag. Its peak bolometric luminosity is derived as $1.32 pm 0.13) times 10^{43} $erg s$^{-1}$, corresponding to a $^{56}$Ni mass of $0.51 pm 0.03 M_{odot}$. The light curves of SN 2017fgc are found to exhibit excess emission in the $UBV$ bands in the early nebular phase and pronounced secondary shoulder/maximum features in the $RrIi$ bands. Its spectral evolution is similar to that of HV SNe Ia, with a maximum-light Si II velocity of $15,000 pm 150 $km s$^{-1}$ and a post-peak velocity gradient of $sim$ $120 pm 10 $km s$^{-1} $d$^{-1}$. The Fe II and Mg II lines blended near 4300 {AA} and the Fe II, Si II, and Fe III lines blended near 4800 {AA} are obviously stronger than those of normal SNe Ia. Inspecting a large sample reveals that the strength of the two blends in the spectra, and the secondary peak in the $i/r$-band light curves, are found to be positively correlated with the maximum-light Si II velocity. Such correlations indicate that HV SNe~Ia may experience more complete burning in the ejecta and/or that their progenitors have higher metallicity. Examining the birthplace environment of SN 2017fgc suggests that it likely arose from a stellar environment with young and high-metallicity populations.
We present $UBVRI$ CCD photometry and optical spectra of the type Ia supernova SN 2003hx which appeared in the galaxy NGC 2076, obtained till $sim$ 146 days after the epoch of $B$ band maximum. The supernova reached at maximum brightness in $B$ band on JD 245 2893 $pm$ 1.0 with an apparent magnitude of 14.92 $pm$ 0.01 mag which was estimated by making template fits to the light curves. SN 2003hx is an example of a highly reddened supernova with $E(B-V)$ = 0.56 $pm$ 0.23. We estimate $R_v$ = 1.97 $pm$ 0.54 which indicates the small size of dust particles as compared to their galactic counterparts. The luminosity decline rate is $Delta m_{15}(B)$ = 1.17 $pm$ 0.12 mag and the absolute $B$ band magnitude obtained from the luminosity versus decline rate relation (Phillips et al. 1999) is $M^B_{max}$ = -19.20 $pm$ 0.18 mag. The peak bolometric luminosity indicates that $sim$ 0.66 $M_odot$ mass of $^{56}$ Ni was ejected by the supernova. The spectral evolution indicates the supernova to be a normal type Ia event.
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