arXiv subjects

I. Arcavi

Publications and source records attributed to I. Arcavi.

At least 91 records · Page 5Linked to original sources

arXiv2018

SN 2016X: A Type II-P Supernova with A Signature of Shock Breakout from Explosion of A Massive Red Supergiant

We present extensive ultraviolet (UV) and optical photometry, as well as dense optical spectroscopy for type II Plateau (IIP) supernova SN 2016X that exploded in the nearby ($\sim$ 15 Mpc) spiral galaxy UGC 08041. The observations span the period from 2 to 180 days after the explosion; in particular, the Swift UV data probably captured the signature of shock breakout associated with the explosion of SN 2016X. It shows very strong UV emission during the first week after explosion, with contribution of $\sim$ 20 -- 30% to the bolometric luminosity (versus $\lesssim$ 15% for normal SNe IIP). Moreover, we found that this supernova has an unusually long rise time of about 12.6 $\pm$ 0.5 days in the $R$ band (versus $\sim$ 7.0 days for typical SNe IIP). The optical light curves and spectral evolution are quite similar to the fast-declining type IIP object SN 2013ej, except that SN 2016X has a relatively brighter tail. Based on the evolution of photospheric temperature as inferred from the $Swift$ data in the early phase, we derive that the progenitor of SN 2016X has a radius of about 930 $\pm$ 70 R$_{\odot}$. This large-size star is expected to be a red supergiant star with an initial mass of $\gtrsim$ 19 -- 20 M$_{\odot}$ based on the mass $--$ radius relation of the Galactic red supergiants, and it represents one of the most largest and massive progenitors found for SNe IIP.

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arXiv2017

X-ray Brightening and UV Fading of Tidal Disruption Event ASASSN-15oi

We present late-time observations by Swift and XMM-Newton of the tidal disruption event (TDE) ASASSN-15oi that reveal that the source brightened in the X-rays by a factor of $\sim10$ one year after its discovery, while it faded in the UV/optical by a factor of $\sim 100$. The XMM-Newton observations measure a soft X-ray blackbody component with $kT_{\rm bb} \sim 45$ eV, corresponding to radiation from several gravitational radii of a central $\sim 10^6 M_\odot$ black hole. The last Swift epoch taken almost 600 days after discovery shows that the X-ray source has faded back to its levels during the UV/optical peak. The timescale of the X-ray brightening suggests that the X-ray emission could be coming from delayed accretion through a newly forming debris disk, and that the prompt UV/optical emission is from the prior circularization of the disk through stream-stream collisions. The lack of spectral evolution during the X-ray brightening disfavors ionization breakout of a TDE "veiled" by obscuring material. This is the first time a TDE has been shown to have a delayed peak in soft X-rays relative to the UV/optical peak, which may be the first clear signature of the real-time assembly of a nascent accretion disk, and provides strong evidence for the origin of the UV/optical emission from circularization, as opposed to reprocessed emission of accretion radiation.

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arXiv2017

On the nature of Hydrogen-rich Superluminous Supernovae

We present two hydrogen-rich superluminous supernovae (SLSNe), namely SN2013hx and PS15br. These objects, together with SN2008es are the only SLSNe showing a distinct, broad Halpha feature during the photospheric phase and also do not show any sign of strong interaction between fast-moving ejecta and circumstellar shells in their early spectra. Despite PS15br peak luminosity is fainter than the other two objects, the spectrophotometric evolution is similar to SN2013hx and different than any other supernova in a similar luminosity space. We group all of them as SLSNe II and hence distinct from the known class of SLSN IIn. Both transients show a strong, multi-component Halpha emission after 200 days past maximum which we interpret as an indication of interaction of the ejecta with an asymmetric, clumpy circumstellar material. The spectra and photometric evolution of the two objects are similar to type II supernovae, although they have much higher luminosity and evolve on slower timescales. This is qualitatively similar to how SLSNe I compare with normal type Ic in that the former are brighter and evolve more slowly. We apply a magnetar and an interaction semi-analytical codes to fit the light curves of our two objects and SN2008es. The overall observational dataset would tend to favour the magnetar, or central engine, model as the source of the peak luminosity although the clear signature of late-time interaction indicates that interaction can play a role in the luminosity evolution of SLSNe II at some phases.

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arXiv2017

The early detection and follow-up of the highly obscured Type II supernova 2016ija/DLT16am

We present our analysis of the Type II supernova DLT16am (SN~2016ija). The object was discovered during the ongoing $\rm{D}<40\,\rm{Mpc}$ (DLT40) one day cadence supernova search at $r\sim20.1\,\rm{mag}$ in the `edge-on' nearby ($D=20.0\pm1.9\,\rm{Mpc}$) galaxy NGC~1532. The subsequent prompt and high-cadenced spectroscopic and photometric follow-up revealed a highly extincted transient, with $E(B-V)=1.95\pm0.15\,\rm{mag}$, consistent with a standard extinction law with $R_V=3.1$ and a bright ($M_V=-18.49\pm0.65\,\rm{mag}$) absolute peak-magnitude. The comparison of the photometric features with those of large samples of Type II supernovae reveals a fast rise for the derived luminosity and a relatively short plateau phase, with a slope of $S_{50V}=0.84\pm0.04\,\rm{mag}/50\,\rm{d}$ consistent with the photometric properties typical of those of fast declining Type II supernovae. Despite the large uncertainties on the distance and the extinction in the direction of DLT16am, the measured photospheric expansion velocity and the derived absolute $V$-band magnitude at $\sim50\,\rm{d}$ after the explosion match the existing luminosity-velocity relation for Type II supernovae.

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arXiv2017

LSQ14efd: observations of the cooling of a shock break-out event in a type Ic Supernova

We present the photometric and spectroscopic evolution of the type Ic supernova LSQ14efd, discovered by the La Silla QUEST survey and followed by PESSTO. LSQ14efd was discovered few days after explosion and the observations cover up to ~100 days. The early photometric points show the signature of the cooling of the shock break-out event experienced by the progenitor at the time of the supernova explosion, one of the first for a type Ic supernova. A comparison with type Ic supernova spectra shows that LSQ14efd is quite similar to the type Ic SN 2004aw. These two supernovae have kinetic energies that are intermediate between standard Ic explosions and those which are the most energetic explosions known (e.g. SN 1998bw). We computed an analytical model for the light-curve peak and estimated the mass of the ejecta 6.3 +/- 0.5 Msun, a synthesized nickel mass of 0.25 Msun and a kinetic energy of Ekin = 5.6 +/- 0.5 x 10^51 erg. No connection between LSQ14efd and a GRB event could be established. However we point out that the supernova shows some spectroscopic similarities with the peculiar SN-Ia 1999ac and the SN-Iax SN 2008A. A core-collapse origin is most probable considering the spectroscopic, photometric evolution and the detection of the cooling of the shock break-out.

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arXiv2017

iPTF16fnl: a faint and fast tidal disruption event in an E+A galaxy

We present ground-based and \textit{Swift} observations of iPTF16fnl, a likely tidal disruption event (TDE) discovered by the intermediate Palomar Transient Factory (iPTF) survey at 66.6 Mpc. The lightcurve of the object peaked at absolute $M_g=-17.2$ mag. The maximum bolometric luminosity (from optical and UV) was $L_p~\simeq~(1.0\,\pm\,0.15) \times 10^{43}$ erg/s, an order of magnitude fainter than any other optical TDE discovered so far. The luminosity in the first 60 days is consistent with an exponential decay, with $L \propto e^{-(t-t_0)/τ}$, where $t_0$=~57631.0 (MJD) and $τ\simeq 15$ days. The X-ray shows a marginal detection at $L_X=2.4^{1.9}_{-1.1}\times 10^{39}$ erg/s (\textit{Swift} X-ray Telescope). No radio counterpart was detected down to 3$σ$, providing upper limits for monochromatic radio luminosity of $νL_ν < 2.3\times10^{36}$ erg/s and $νL_ν<1.7\times 10^{37}$ erg/s (VLA, 6.1 and 22 GHz). The blackbody temperature, obtained from combined \textit{Swift} UV and optical photometry, shows a constant value of 19,000 K. The transient spectrum at peak is characterized by broad He II and H$α$ emission lines, with an FWHM of about 14,000 km/s and 10,000 km/s respectively. He I lines are also detected at $λλ$ 5875 and 6678. The spectrum of the host is dominated by strong Balmer absorption lines, which are consistent with a post-starburst (E+A) galaxy with an age of $\sim$650 Myr and solar metallicity. The characteristics of iPTF16fnl make it an outlier on both luminosity and decay timescales, as compared to other optically selected TDEs. The discovery of such a faint optical event suggests a higher rate of tidal disruptions, as low luminosity events may have gone unnoticed in previous searches.

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arXiv2017

Revisiting optical tidal disruption events with iPTF16axa

We report the discovery by the intermediate Palomar Transient Factory (iPTF) of a candidate tidal disruption event (TDE) iPTF16axa at $z=0.108$, and present its broadband photometric and spectroscopic evolution from 3 months of follow-up observations with ground-based telescopes and Swift. The light curve is well fitted with a $t^{-5/3}$ decay, and we constrain the rise-time to peak to be $<$49 rest-frame days after disruption, which is roughly consistent with the fallback timescale expected for the $\sim 5\times$10$^{6}$ $M_\odot$ black hole inferred from the stellar velocity dispersion of the host galaxy. The UV and optical spectral energy distribution (SED) is well described by a constant blackbody temperature of T$\sim$ 3$\times$10$^4$ K over the monitoring period, with an observed peak luminosity of 1.1$\times$10$^{44}$ erg s$^{-1}$. The optical spectra are characterized by a strong blue continuum and broad HeII and H$α$ lines characteristic of TDEs. We compare the photometric and spectroscopic signatures of iPTF16axa with 11 TDE candidates in the literature with well-sampled optical light curves. Based on a single-temperature fit to the optical and near-UV photometry, most of these TDE candidates have peak luminosities confined between log(L [erg s$^{-1}$]) = 43.4-44.4, with constant temperatures of a few $\times 10^{4}$ K during their power-law declines, implying blackbody radii on the order of ten times the tidal disruption radius, that decrease monotonically with time. For TDE candidates with hydrogen and helium emission, the high helium-to-hydrogen ratios suggest that the emission arises from high-density gas, where nebular arguments break down. We find no correlation between the peak luminosity and the black hole mass, contrary to the expectations for TDEs to have $\dot{M} \propto M_{\rm BH}^{-1/2}$.

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arXiv2017

Confined Dense Circumstellar Material Surrounding a Regular Type II Supernova: The Unique Flash-Spectroscopy Event of SN 2013fs

With the advent of new wide-field, high-cadence optical transient surveys, our understanding of the diversity of core-collapse supernovae has grown tremendously in the last decade. However, the pre-supernova evolution of massive stars, that sets the physical backdrop to these violent events, is theoretically not well understood and difficult to probe observationally. Here we report the discovery of the supernova iPTF13dqy = SN 2013fs, a mere ~3 hr after explosion. Our rapid follow-up observations, which include multiwavelength photometry and extremely early (beginning at ~6 hr post-explosion) spectra, map the distribution of material in the immediate environment (<~ 10^15 cm) of the exploding star and establish that it was surrounded by circumstellar material (CSM) that was ejected during the final ~1 yr prior to explosion at a high rate, around 10^-3 solar masses per year. The complete disappearance of flash-ionised emission lines within the first several days requires that the dense CSM be confined to within <~ 10^15 cm, consistent with radio non-detections at 70--100 days. The observations indicate that iPTF13dqy was a regular Type II SN; thus, the finding that the probable red supergiant (RSG) progenitor of this common explosion ejected material at a highly elevated rate just prior to its demise suggests that pre-supernova instabilities may be common among exploding massive stars.

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arXiv2017

The progenitor and early evolution of the Type IIb SN 2016gkg

We report initial observations and analysis on the Type IIb SN~2016gkg in the nearby galaxy NGC~613. SN~2016gkg exhibited a clear double-peaked light curve during its early evolution, as evidenced by our intensive photometric follow-up campaign. SN~2016gkg shows strong similarities with other Type IIb SNe, in particular with respect to the \he~emission features observed in both the optical and near infrared. SN~2016gkg evolved faster than the prototypical Type~IIb SN~1993J, with a decline similar to that of SN~2011dh after the first peak. The analysis of archival {\it Hubble Space Telescope} images indicate a pre-explosion source at SN~2016gkg's position, suggesting a progenitor star with a $\sim$mid F spectral type and initial mass $15-20$\msun, depending on the distance modulus adopted for NGC~613. Modeling the temperature evolution within $5\,\rm{days}$ of explosion, we obtain a progenitor radius of $\sim\,48-124$\rsun, smaller than that obtained from the analysis of the pre-explosion images ($240-320$\rsun).

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arXiv2016

The Superluminous Transient ASASSN-15lh as a Tidal Disruption Event from a Kerr Black Hole

When a star passes within the tidal radius of a supermassive black hole, it will be torn apart. For a star with the mass of the Sun ($M_\odot$) and a non-spinning black hole with a mass $<10^8 M_\odot$, the tidal radius lies outside the black hole event horizon and the disruption results in a luminous flare. Here we report observations over a period of 10 months of a transient, hitherto interpreted as a superluminous supernova. Our data show that the transient rebrightened substantially in the ultraviolet and that the spectrum went through three different spectroscopic phases without ever becoming nebular. Our observations are more consistent with a tidal disruption event than a superluminous supernova because of the temperature evolution, the presence of highly ionised CNO gas in the line of sight and our improved localisation of the transient in the nucleus of a passive galaxy, where the presence of massive stars is highly unlikely. While the supermassive black hole has a mass $> 10^8 M_\odot$, a star with the same mass as the Sun could be disrupted outside the event horizon if the black hole were spinning rapidly. The rapid spin and high black hole mass can explain the high luminosity of this event.

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arXiv2016

Early observations of the nearby type Ia supernova SN 2015F

We present photometry and time-series spectroscopy of the nearby type Ia supernova (SN Ia) SN 2015F over $-16$ days to $+80$ days relative to maximum light, obtained as part of the Public ESO Spectroscopic Survey of Transient Objects (PESSTO). SN 2015F is a slightly sub-luminous SN Ia with a decline rate of $Δm15(B)=1.35 \pm 0.03$ mag, placing it in the region between normal and SN 1991bg-like events. Our densely-sampled photometric data place tight constraints on the epoch of first light and form of the early-time light curve. The spectra exhibit photospheric C II $λ6580$ absorption until $-4$ days, and high-velocity Ca II is particularly strong at $<-10$ days at expansion velocities of $\simeq$23000\kms. At early times, our spectral modelling with syn++ shows strong evidence for iron-peak elements (Fe II, Cr II, Ti II, and V II) expanding at velocities $>14000$ km s$^{-1}$, suggesting mixing in the outermost layers of the SN ejecta. Although unusual in SN Ia spectra, including V II in the modelling significantly improves the spectral fits. Intriguingly, we detect an absorption feature at $\sim$6800 Å that persists until maximum light. Our favoured explanation for this line is photospheric Al II, which has never been claimed before in SNe Ia, although detached high-velocity C II material could also be responsible. In both cases the absorbing material seems to be confined to a relatively narrow region in velocity space. The nucleosynthesis of detectable amounts of Al II would argue against a low-metallicity white dwarf progenitor. We also show that this 6800 Å feature is weakly present in other normal SN Ia events, and common in the SN 1991bg-like sub-class.

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arXiv2016

OGLE16aaa - a Signature of a Hungry Super Massive Black Hole

We present the discovery and first three months of follow-up observations of a currently on-going unusual transient detected by the OGLE-IV survey, located in the centre of a galaxy at redshift z=0.1655. The long rise to absolute magnitude of -20.5 mag, slow decline, very broad He and H spectral features make OGLE16aaa similar to other optical/UV Tidal Disruption Events (TDEs). Weak narrow emission lines in the spectrum and archival photometric observations suggest the host galaxy is a weak-line Active Galactic Nucleus (AGN), which has been accreting at higher rate in the past. OGLE16aaa, along with SDSS J0748, seems to form a sub-class of TDEs by weakly or recently active super-massive black holes (SMBHs). This class might bridge the TDEs by quiescent SMBHs and flares observed as "changing-look QSOs", if we interpret the latter as TDEs. If this picture is true, the previously applied requirement for identifying a flare as a TDE that it had to come from an inactive nucleus, could be leading to observational bias in TDE selection, thus affecting TDE-rate estimations.

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arXiv2016

Superluminous supernova 2015bn in the nebular phase: evidence for the engine-powered explosion of a stripped massive star

We present nebular-phase imaging and spectroscopy for the hydrogen-poor superluminous supernova SN 2015bn, at redshift z=0.1136, spanning +250-400 d after maximum light. The light curve exhibits a steepening in the decline rate from 1.4 mag/(100 d) to 1.7 mag/(100 d), suggestive of a significant decrease in the opacity. This change is accompanied by a transition from a blue continuum superposed with photospheric absorption lines to a nebular spectrum dominated by emission lines of oxygen, calcium and magnesium. There are no obvious signatures of circumstellar interaction or large nickel mass. We show that the spectrum at +400 d is virtually identical to a number of energetic Type Ic supernovae such as SN 1997dq, SN 2012au, and SN 1998bw, indicating similar core conditions and strengthening the link between `hypernovae'/long gamma-ray bursts and superluminous supernovae. A single explosion mechanism may unify these events that span absolute magnitudes of -22 < M_B < -17. Both the light curve and spectrum of SN 2015bn are consistent with an engine-driven explosion ejecting 7-30 M$_\odot$ of oxygen-dominated ejecta (for reasonable choices in temperature and opacity). A strong and relatively narrow O II $λ$7774 line, seen in a number of these energetic events but not in normal supernovae, may point to an inner shell that is the signature of a central engine.

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arXiv2016

M31N 2008-12a - the remarkable recurrent nova in M31: Pan-chromatic observations of the 2015 eruption

The Andromeda Galaxy recurrent nova M31N 2008-12a had been observed in eruption ten times, including yearly eruptions from 2008-2014. With a measured recurrence period of $P_\mathrm{rec}=351\pm13$ days (we believe the true value to be half of this) and a white dwarf very close to the Chandrasekhar limit, M31N 2008-12a has become the leading pre-explosion supernova type Ia progenitor candidate. Following multi-wavelength follow-up observations of the 2013 and 2014 eruptions, we initiated a campaign to ensure early detection of the predicted 2015 eruption, which triggered ambitious ground and space-based follow-up programs. In this paper we present the 2015 detection; visible to near-infrared photometry and visible spectroscopy; and ultraviolet and X-ray observations from the Swift observatory. The LCOGT 2m (Hawaii) discovered the 2015 eruption, estimated to have commenced at Aug. $28.28\pm0.12$ UT. The 2013-2015 eruptions are remarkably similar at all wavelengths. New early spectroscopic observations reveal short-lived emission from material with velocities $\sim13000$ km s$^{-1}$, possibly collimated outflows. Photometric and spectroscopic observations of the eruption provide strong evidence supporting a red giant donor. An apparently stochastic variability during the early super-soft X-ray phase was comparable in amplitude and duration to past eruptions, but the 2013 and 2015 eruptions show evidence of a brief flux dip during this phase. The multi-eruption Swift/XRT spectra show tentative evidence of high-ionization emission lines above a high-temperature continuum. Following Henze et al. (2015a), the updated recurrence period based on all known eruptions is $P_\mathrm{rec}=174\pm10$ d, and we expect the next eruption of M31N 2008-12a to occur around mid-Sep. 2016.

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arXiv2016

SN 2015bn: a detailed multi-wavelength view of a nearby superluminous supernova

We present observations of SN 2015bn (= PS15ae = CSS141223-113342+004332 = MLS150211-113342+004333), a Type I superluminous supernova (SLSN) at redshift $z=0.1136$. As well as being one of the closest SLSNe I yet discovered, it is intrinsically brighter ($M_U\approx-23.1$) and in a fainter galaxy ($M_B\approx-16.0$) than other SLSNe at $z\sim0.1$. We used this opportunity to collect the most extensive dataset for any SLSN I to date, including densely-sampled spectroscopy and photometry, from the UV to the NIR, spanning $-$50 to +250 days from optical maximum. SN 2015bn fades slowly, but exhibits surprising undulations in the light curve on a timescale of 30-50 days, especially in the UV. The spectrum shows extraordinarily slow evolution except for a rapid transformation between +7 and +20-30 days. No narrow emission lines from slow-moving material are observed at any phase. We derive physical properties including the bolometric luminosity, and find slow velocity evolution and non-monotonic temperature and radial evolution. A deep radio limit rules out a healthy off-axis gamma-ray burst, and places constraints on the pre-explosion mass loss. The data can be consistently explained by a $\gtrsim10\,{\rm M}_\odot$ stripped progenitor exploding with $\sim 10^{51}\,$erg kinetic energy, forming a magnetar with a spin-down timescale of $\sim20$ days (thus avoiding a gamma-ray burst) that reheats the ejecta and drives ionization fronts. The most likely alternative scenario -- interaction with $\sim20\,{\rm M}_\odot$ of dense, inhomogeneous circumstellar material -- can be tested with continuing radio follow-up.

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arXiv2016

PTF12os and iPTF13bvn. Two stripped-envelope supernovae from low-mass progenitors in NGC 5806

We investigate two stripped-envelope supernovae (SNe) discovered in the nearby galaxy NGC 5806 by the (i)PTF. These SNe, designated PTF12os/SN 2012P and iPTF13bvn, exploded at a similar distance from the host-galaxy center. We classify PTF12os as a Type IIb SN based on our spectral sequence; iPTF13bvn has previously been classified as Type Ib having a likely progenitor with zero age main sequence (ZAMS) mass below ~17 solar masses. Our main objective is to constrain the explosion parameters of iPTF12os and iPTF13bvn, and to put constraints on the SN progenitors. We present comprehensive datasets on the SNe, and introduce a new reference-subtraction pipeline (FPipe) currently in use by the iPTF. We perform a detailed study of the light curves (LCs) and spectral evolution of the SNe. The bolometric LCs are modeled using the hydrodynamical code HYDE. We use nebular models and late-time spectra to constrain the ZAMS mass of the progenitors. We perform image registration of ground-based images of PTF12os to archival HST images of NGC 5806 to identify a potential progenitor candidate. Our nebular spectra of iPTF13bvn indicate a low ZAMS mass of ~12 solar masses for the progenitor. The late-time spectra of PTF12os are consistent with a ZAMS mass of ~15 solar masses. We successfully identify a progenitor candidate to PTF12os using archival HST images. This source is consistent with being a cluster of massive stars. Our hydrodynamical modeling suggests that the progenitor of PTF12os had a compact He core with a mass of 3.25 solar masses, and that 0.063 solar masses of strongly mixed 56Ni was synthesized. Spectral comparisons to the Type IIb SN 2011dh indicate that the progenitor of PTF12os was surrounded by a hydrogen envelope with a mass lower than 0.02 solar masses. We also find tentative evidence that the progenitor of iPTF13bvn could have been surrounded by a small amount of hydrogen.

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arXiv2016

The multi-faceted Type II-L supernova 2014G from pre-maximum to nebular phase

We present multi-band ultraviolet, optical, and near-infrared photometry, along with visual-wavelength spectroscopy, of supernova (SN) 2014G in the nearby galaxy NGC 3448 (25 Mpc). The early-phase spectra show strong emission lines of the high ionisation species He II/N IV/C IV during the first 2-3 d after explosion, traces of a metal-rich CSM probably due to pre-explosion mass loss events. These disappear by day 9 and the spectral evolution then continues matching that of normal Type II SNe. The post-maximum light curve declines at a rate typical of Type II-L class. The extensive photometric coverage tracks the drop from the photospheric stage and constrains the radioactive tail, with a steeper decline rate than that expected from the $^{56}$Co decay if $γ$-rays are fully trapped by the ejecta. We report the appearance of an unusual feature on the blue-side of H$α$ after 100 d, which evolves to appear as a flat spectral feature linking H$α$ and the O I doublet. This may be due to interaction of the ejecta with a strongly asymmetric, and possibly bipolar CSM. Finally, we report two deep spectra at ~190 and 340 d after explosion, the latter being arguably one of the latest spectra for a Type II-L SN. By modelling the spectral region around the Ca II, we find a supersolar Ni/Fe production. The strength of the O I $λλ$6300,6363 doublet, compared with synthetic nebular spectra, suggests a progenitor with a zero-age main-sequence mass between 15 and 19 M$_\odot$.

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arXiv2016

The diversity of Type II supernova versus the similarity in their progenitors

High-quality collections of Type II supernova (SN) light curves are scarce because they evolve for hundreds of days, making follow-up observations time consuming and often extending over multiple observing seasons. In light of these difficulties, the diversity of SNe II is not fully understood. Here we present ultraviolet and optical photometry of 12 SNe II monitored by the Las Cumbres Observatory Global Telescope Network (LCOGT) during 2013-2014, and compare them with previously studied SNe having well-sampled light curves. We explore SN II diversity by searching for correlations between the slope of the linear light-curve decay after maximum light (historically used to divide SNe II into IIL and IIP) and other measured physical properties. While SNe IIL are found to be on average more luminous than SNe IIP, SNe IIL do not appear to synthesize more 56Ni than SNe IIP. Finally, optical nebular spectra obtained for several SNe in our sample are found to be consistent with models of red supergiant progenitors in the 12-16 Msun range. Consequently, SNe IIL appear not to account for the deficit of massive red supergiants as SN II progenitors.

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