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Register a new userTwo transitional type~Ia supernovae located in the Fornax cluster member NGC 1404: SN 2007on and SN 2011iv
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We present an analysis of ultraviolet (UV) to near-infrared observations of the fast-declining Type Ia supernovae (SNe Ia) 2007on and 2011iv, hosted by the Fornax cluster member NGC 1404. The B-band light curves of SN 2007on and SN 2011iv are characterised by dm_15(B) decline-rate values of 1.96 mag and 1.77 mag, respectively. Although they have similar decline rates, their peak B- and H-band magnitudes differ by ~0.60 mag and ~0.35 mag, respectively. After correcting for the luminosity vs. decline rate and the luminosity vs. colour relations, the peak B-band and H-band light curves provide distances that differ by ~14% and ~9%, respectively. These findings serve as a cautionary tale for the use of transitional SNe Ia located in early-type hosts in the quest to measure cosmological parameters. Interestingly, even though SN 2011iv is brighter and bluer at early times, by three weeks past maximum and extending over several months, its B-V colour is 0.12 mag redder than that of SN 2007on. To reconcile this unusual behaviour, we turn to guidance from a suite of spherical one-dimensional Chandrasekhar-mass delayed-detonation explosion models. In this context, 56Ni production depends on both the so-called transition density and the central density of the progenitor white dwarf. To first order, the transition density drives the luminosity-width relation, while the central density is an important second-order parameter. Within this context, the differences in the B-V color evolution along the Lira regime suggests the progenitor of SN~2011iv had a higher central density than SN~2007on.
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We present photometric and spectroscopic observations of SN 2013aa and SN 2017cbv, two nearly identical type Ia supernovae (SNe Ia) in the host galaxy NGC 5643. The optical photometry has been obtained using the same telescope and instruments used by the Carnegie Supernova Project. This eliminates most instrumental systematics and provides light curves in a stable and well-understood photometric system. Having the same host galaxy also eliminates systematics due to distance and peculiar velocity, providing an opportunity to directly test the relative precision of SNe Ia as standard candles. The two SNe have nearly identical decline rates, negligible reddening, and remarkably similar spectra and, at a distance of $sim 20$ Mpc, are ideal as potential calibrators for the absolute distance using primary indicators such as Cepheid variables. We discuss to what extent these two SNe can be considered twins and compare them with other supernova siblings in the literature and their likely progenitor scenarios. Using 12 galaxies that hosted 2 or more SNe~Ia, we find that when using SNe~Ia, and after accounting for all sources of observational error, one gets consistency in distance to 3 percent.
The Type Ia supernova (SN Ia) SN 2000cx was one of the most peculiar transients ever discovered, with a rise to maximum brightness typical of a SN Ia, but a slower decline and a higher photospheric temperature. Thirteen years later SN 2013bh (aka iPTF13abc), a near identical twin, was discovered and we obtained optical and near-IR photometry and low-resolution optical spectroscopy from discovery until about 1 month past r-band maximum brightness. The spectra of both objects show iron-group elements (Co II, Ni II, Fe II, Fe III, and high-velocity features [HVFs] of Ti II), intermediate-mass elements (Si II, Si III, and S II), and separate normal velocity features (~12000 km/s) and HVFs (~24000 km/s) of Ca II. Persistent absorption from Fe III and Si III, along with the colour evolution, imply high blackbody temperatures for SNe 2013bh and 2000cx (~12000 K). Both objects lack narrow Na I D absorption and exploded in the outskirts of their hosts, indicating that the SN environments were relatively free of interstellar or circumstellar material and may imply that the progenitors came from a relatively old and low-metallicity stellar population. Models of SN 2000cx, seemingly applicable to SN 2013bh, imply the production of up to ~1 M_Sun of Ni-56 and (4.3-5.5)e-3 M_Sun of fast-moving Ca ejecta.
We have been searching for surviving companions of progenitors of Galactic Type-Ia supernovae, in particular SN 1572 and SN 1006. These companion stars are expected to show peculiarities: (i) to be probably more luminous than the Sun, (ii) to have high radial velocity and proper motion, (iii) to be possibly enriched in metals from the SNIa ejecta, and (iv) to be located at the distance of the SNIa remnant. We have been characterizing possible candidate stars using high-resolution spectroscopic data taken at 10m-Keck and 8.2m-VLT facilities. We have identified a very promising candidate companion (Tycho G) for SN 1572, but we have not found any candidate companion for SN 1006, suggesting that SN event occurred in 1006 could have been the result of the merging of two white dwarfs. Adding these results to the evidence from the other direct searches, the clear minority of cases (20% or less) seem to disfavour the single-degenerate channel or that preferentially the single-degenerate escenario would involve main-sequence companions less massive than the Sun. Therefore, it appears to be very important to continue investigating these and other Galactic Type-Ia SNe such as the Johannes Kepler SN 1604.
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.
We present extensive spectroscopic observations for one of the closest type Ia supernovae (SNe Ia), SN 2014J discovered in M82, ranging from 10.4 days before to 473.2 days after B-band maximum light. The diffuse interstellar band (DIB) features detected in a high-resolution spectrum allow an estimate of line-of-sight extinction as Av=1.9+/-0.6 mag. Spectroscopically, SN 2014J can be put into the high-velocity (HV) subgroup in Wangs classification with a velocity of Si~II 6355 at maximum light as about 12200 km/s, but has a low velocity gradient (LVG, following Benettis classification) as 41+/-2 km/s/day, which is inconsistent with the trend that HV SNe Ia generally have larger velocity gradients. We find that the HV SNe Ia with LVGs tend to have relatively stronger Si III (at ~4400 Angstrom) absorptions in early spectra, larger ratios of S II 5468 to S II 5640, and weaker Si II 5972 absorptions compared to their counterparts with similar velocities but high velocity gradients. This shows that the HV+LVG subgroup of SNe Ia may have intrinsically higher photospheric temperature, which indicates that their progenitors may experience more complete burning in the explosions relative to the typical HV SNe Ia.
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