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Register a new userLow-luminosity Type IIP Supernova 2016bkv with early-phase circumstellar interaction
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We present optical and near-infrared observations of a low-luminosity Type IIP supernova (SN) 2016bkv from the initial rising phase to the plateau phase. Our observations show that the end of the plateau is extended to $gtrsim 140$ days since the explosion, indicating that this SN takes one of the longest time to finish the plateau phase. among Type IIP SNe (SNe IIP), including low-luminosity (LL) SNe IIP. The line velocities of various ions at the middle of the plateau phase are as low as 1,000--1,500 km s$^{-1}$, which is the lowest even among LL SNe IIP. These measurements imply that the ejecta mass in SN 2016bkv is larger than that of the well-studied LL IIP SN 2003Z. In the early phase, SN 2016bkv shows a strong bump in the light curve. In addition, the optical spectra in this bump phase exhibit a blue continuum accompanied with a narrow H$alpha$ emission line. These features indicate an interaction between the SN ejecta and the circumstellar matter (CSM) as in SNe IIn. Assuming the ejecta-CSM interaction scenario, the mass loss rate is estimated to be $sim 1.7 times 10^{-2} M_{odot}$ yr$^{-1}$ within a few years before the SN explosion. This is comparable to or even larger than the largest mass loss rate observed for the Galactic red supergiants ($sim 10^{-3} M_{odot}$ yr$^{-1}$ for VY CMa). We suggest that the progenitor star of SN 2016bkv experienced a violent mass loss just before the SN explosion.
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While interaction with circumstellar material is known to play an important role in Type IIn supernovae (SNe), analyses of the more common SNe IIP and IIL have not traditionally included interaction as a significant power source. However, recent campaigns to observe SNe within days of explosion have revealed narrow emission lines of high-ionization species in the earliest spectra of luminous SNe II of all subclasses. These flash ionization features indicate the presence of a confined shell of material around the progenitor star. Here we present the first low-luminosity (LL) SN to show flash ionization features, SN 2016bkv. This SN peaked at $M_V = -16$ mag and has H{alpha} expansion velocities under 1350 km/s around maximum light, placing it at the faint/slow end of the distribution of SNe IIP (similar to SN 2005cs). The light-curve shape of SN 2016bkv is also extreme among SNe IIP. A very strong initial peak could indicate additional luminosity from circumstellar interaction. A very small fall from the plateau to the nickel tail indicates unusually large production of radioactive nickel compared to other LL SNe IIP. A comparison between nebular spectra of SN 2016bkv and models raises the possibility that SN 2016bkv is an electron-capture supernova.
Hydrogen-rich, core-collapse supernovae are typically divided into four classes: IIP, IIL, IIn, and IIb. In general, interaction with circumstellar material is only considered for Type IIn supernovae. However, recent hydrodynamic modeling of IIP and IIL supernovae requires circumstellar material to reproduce their early light curves. In this scenario, IIL supernovae experience large amounts of mass loss before exploding. We test this hypothesis on ASASSN-15oz, a Type IIL supernova. With extensive follow-up in the X- ray, UV, optical, IR, and radio we present our search for signs of interaction, and the mass-loss history indicated by their detection. We find evidence of short-lived intense mass-loss just prior to explosion from light curve modeling, amounting in 1.5 M$_{odot}$ of material within 1800 R$_{odot}$ of the progenitor. We also detect the supernova in the radio, indicating mass-loss rates of $10^{-6}-10^{-7}$ M$_{odot}$ yr$^{-1}$ prior to the extreme mass-loss period. Our failure to detect the supernova in the X-ray and the lack of narrow emission lines in the UV, optical, and NIR do not contradict this picture and place an upper limit on the mass-loss rate outside the extreme period of $<10^{-4}$ M$_{odot}$ yr$^{-1}$. This paper highlights the importance gathering comprehensive data on more Type II supernovae to enable detailed modeling of the progenitor and supernova which can elucidate their mass-loss histories and envelope structures and thus inform stellar evolution models.
This paper describes the rapidly evolving and unusual supernova LSQ13ddu, discovered by the La Silla-QUEST survey. LSQ13ddu displayed a rapid rise of just 4.8$pm$0.9 d to reach a peak brightness of $-$19.70$pm$0.02 mag in the $mathit{LSQgr}$ band. Early spectra of LSQ13ddu showed the presence of weak and narrow He I features arising from interaction with circumstellar material (CSM). These interaction signatures weakened quickly, with broad features consistent with those seen in stripped-envelope SNe becoming dominant around two weeks after maximum. The narrow He I velocities are consistent with the wind velocities of luminous blue variables but its spectra lack the typically seen hydrogen features. The fast and bright early light curve is inconsistent with radioactive $^{56}$Ni powering but can be explained through a combination of CSM interaction and an underlying $^{56}$Ni decay component that dominates the later time behaviour of LSQ13ddu. Based on the strength of the underlying broad features, LSQ13ddu appears deficient in He compared to standard SNe Ib.
We present the photometry and spectroscopy of SN 2015an, a Type II Supernova (SN) in IC 2367. The recombination phase of the SN lasts up to $sim$120 d, with a decline rate of 1.24 mag/100d, higher than the typical SNe IIP. The SN exhibits bluer colours than most SNe II, indicating higher ejecta temperatures. The absolute $V$-band magnitude of SN 2015an at 50 d is $-$16.83$pm$0.04 mag, pretty typical for SNe II. However, the $^{56}$Ni mass yield, estimated from the tail $V$-band light curve to be 0.021$pm$0.010 M$_odot$, is comparatively low. The spectral properties of SN 2015an are atypical, with low H$alpha$ expansion velocity and presence of high velocity component of H$alpha$ at early phases. Moreover, the continuum exhibits excess blue flux up to $sim$50 d, which is interpreted as a progenitor metallicity effect. The high velocity feature indicates ejecta-circumstellar material interaction at early phases. The semi-analytical modelling of the bolometric light curve yields a total ejected mass of $sim$12 M$_odot$, a pre-supernova radius of $sim$388~R$_odot$ and explosion energy of $sim$1.8 foe.
We present extensive optical ($UBVRI$, $griz$, and open CCD) and near-infrared ($ZYJH$) photometry for the very nearby Type IIP SN ~2013ej extending from +1 to +461 days after shock breakout, estimated to be MJD $56496.9pm0.3$. Substantial time series ultraviolet and optical spectroscopy obtained from +8 to +135 days are also presented. Considering well-observed SNe IIP from the literature, we derive $UBVRIJHK$ bolometric calibrations from $UBVRI$ and unfiltered measurements that potentially reach 2% precision with a $B-V$ color-dependent correction. We observe moderately strong Si II $lambda6355$ as early as +8 days. The photospheric velocity ($v_{rm ph}$) is determined by modeling the spectra in the vicinity of Fe II $lambda5169$ whenever observed, and interpolating at photometric epochs based on a semianalytic method. This gives $v_{rm ph} = 4500pm500$ km s$^{-1}$ at +50 days. We also observe spectral homogeneity of ultraviolet spectra at +10--12 days for SNe IIP, while variations are evident a week after explosion. Using the expanding photosphere method, from combined analysis of SN 2013ej and SN 2002ap, we estimate the distance to the host galaxy to be $9.0_{-0.6}^{+0.4}$ Mpc, consistent with distance estimates from other methods. Photometric and spectroscopic analysis during the plateau phase, which we estimated to be $94pm7$ days long, yields an explosion energy of $0.9pm0.3times10^{51}$ ergs, a final pre-explosion progenitor mass of $15.2pm4.2$~M$_odot$ and a radius of $250pm70$~R$_odot$. We observe a broken exponential profile beyond +120 days, with a break point at +$183pm16$ days. Measurements beyond this break time yield a $^{56}$Ni mass of $0.013pm0.001$~M$_odot$.
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