409 research outputs found
The nebular spectra of SN 2012aw and constraints on stellar nucleosynthesis from oxygen emission lines
We present nebular phase optical and near-infrared spectroscopy of the Type
IIP supernova SN 2012aw combined with NLTE radiative transfer calculations
applied to ejecta from stellar evolution/explosion models. Our spectral
synthesis models generally show good agreement with the ejecta from a MZAMS =
15 Msun progenitor star. The emission lines of oxygen, sodium, and magnesium
are all consistent with the nucleosynthesis in a progenitor in the 14 - 18 Msun
range. We also demonstrate how the evolution of the oxygen cooling lines of [O
I] 5577 A, [O I] 6300 A, and [O I] 6364 A can be used to constrain the mass of
oxygen in the non-molecularly cooled ashes to < 1 Msun, independent of the
mixing in the ejecta. This constraint implies that any progenitor model of
initial mass greater than 20 Msun would be difficult to reconcile with the
observed line strengths. A stellar progenitor of around MZAMS = 15 Msun can
consistently explain the directly measured luminosity of the progenitor star,
the observed nebular spectra, and the inferred pre-supernova mass-loss rate. We
conclude that there is still no convincing example of a Type IIP explosion
showing the nucleosynthesis expected from a MZAMS > 20 Msun progenitor.Comment: Accepted for publication in MNRA
The luminous late-time emission of the type Ic supernova iPTF15dtg - evidence for powering from a magnetar?
iPTF15dtg is a Type Ic supernova (SN) showing a broad light curve around
maximum light, consistent with massive ejecta if we assume a
radioactive-powering scenario. We study the late-time light curve of iPTF15dtg,
which turned out to be extraordinarily luminous for a stripped-envelope (SE)
SN. We compare the observed light curves to those of other SE SNe and also with
models for the Co decay. We analyze and compare the spectra to nebular
spectra of other SE SNe. We build a bolometric light curve and fit it with
different models, including powering by radioactivity, magnetar powering, as
well as a combination of the two. Between 150 d and 750 d past explosion,
iPTF15dtg's luminosity declined by merely two magnitudes instead of the six
magnitudes expected from Co decay. This is the first
spectroscopically-regular SE SN showing this behavior. The model with both
radioactivity and magnetar powering provides the best fit to the light curve
and appears to be the more realistic powering mechanism. An alternative
mechanism might be CSM interaction. However, the spectra of iPTF15dtg are very
similar to those of other SE SNe, and do not show signs of strong CSM
interaction. iPTF15dtg is the first spectroscopically-regular SE SN whose light
curve displays such clear signs of a magnetar contributing to the powering of
the late time light curve. Given this result, the mass of the ejecta needs to
be revised to a lower value, and therefore the progenitor mass could be
significantly lower than the previously estimated 35 .Comment: 9 pages, 8 figures, accepted for publication in Astronomy and
Astrophysic
A metallicity study of 1987A-like supernova host galaxies
The origin of the blue supergiant (BSG) progenitor of Supernova (SN) 1987A
has long been debated, along with the role that its sub-solar metallicity
played. We now have a sample of 1987A-like SNe that arise from the core
collapse (CC) of BSGs. The metallicity of the explosion sites of the known BSG
SNe is investigated, as well as their association to star-forming regions. Both
indirect and direct metallicity measurements of 13 BSG SN host galaxies are
presented, and compared to those of other CC SN types. Indirect measurements
are based on the known luminosity-metallicity relation and on published
metallicity gradients of spiral galaxies. To provide direct estimates based on
strong line diagnostics, we obtained spectra of each BSG SN host both at the SN
explosion site and at the positions of other HII regions. Continuum-subtracted
Ha images allowed us to quantify the association between BSG SNe and
star-forming regions. BSG SNe explode either in low-luminosity galaxies or at
large distances from the nuclei of luminous hosts. Therefore, their indirectly
measured metallicities are typically lower than those of SNe IIP and Ibc. This
is confirmed by the direct estimates, which show slightly sub-solar values
(12+log(O/H)=8.3-8.4 dex), similar to that of the Large Magellanic Cloud (LMC),
where SN 1987A exploded. However, two SNe (1998A and 2004em) were found at near
solar metallicity. SNe IIb have a metallicity distribution similar to that of
BSG SNe. Finally, the association to star-forming regions is similar among BSG
SNe, SNe IIP and IIn. Our results suggest that LMC metal abundances play a role
in the formation of some 1987A-like SNe. This would naturally fit in a single
star scenario for the progenitors. However, the existence of two events at
nearly solar metallicity suggests that also other channels, e.g. binarity,
contribute to produce BSG SNe.Comment: 28 pages, 17 figures; accepted for publication (Astronomy and
Astrophysics); abstract abridged for arXiv submissio
Constraints on the origin of the first light from SN2014J
We study the very early lightcurve of supernova 2014J (SN 2014J) using the
high-cadence broad-band imaging data obtained by the Kilodegree Extremely
Little Telescope (KELT), which fortuitously observed M 82 around the time of
the explosion, starting more than two months prior to detection, with up to 20
observations per night. These observations are complemented by observations in
two narrow-band filters used in an H survey of nearby galaxies by the
intermediate Palomar Transient Factory (iPTF) that also captured the first days
of the brightening of the \sn. The evolution of the lightcurves is consistent
with the expected signal from the cooling of shock heated material of large
scale dimensions, \gsim 1 R_{\odot}. This could be due to heated material of
the progenitor, a companion star or pre-existing circumstellar environment,
e.g., in the form of an accretion disk. Structure seen in the lightcurves
during the first days after explosion could also originate from radioactive
material in the outer parts of an exploding white dwarf, as suggested from the
early detection of gamma-rays. The model degeneracy translates into a
systematic uncertainty of days on the estimate of the first light
from SN 2014J.Comment: Accepted by ApJ. Companion paper by Siverd et al, arXiv:1411.415
Metallicity at the explosion sites of interacting transients
Context. Some circumstellar-interacting (CSI) supernovae (SNe) are produced
by the explosions of massive stars that have lost mass shortly before the SN
explosion. There is evidence that the precursors of some SNe IIn were luminous
blue variable (LBV) stars. For a small number of CSI SNe, outbursts have been
observed before the SN explosion. Eruptive events of massive stars are named as
SN impostors (SN IMs) and whether they herald a forthcoming SN or not is still
unclear. The large variety of observational properties of CSI SNe suggests the
existence of other progenitors, such as red supergiant (RSG) stars with
superwinds. Furthermore, the role of metallicity in the mass loss of CSI SN
progenitors is still largely unexplored. Aims. Our goal is to gain insight on
the nature of the progenitor stars of CSI SNe by studying their environments,
in particular the metallicity at their locations. Methods. We obtain
metallicity measurements at the location of 60 transients (including SNe IIn,
SNe Ibn, and SN IMs), via emission-line diagnostic on optical spectra obtained
at the Nordic Optical Telescope and through public archives. Metallicity values
from the literature complement our sample. We compare the metallicity
distributions among the different CSI SN subtypes and to those of other
core-collapse SN types. We also search for possible correlations between
metallicity and CSI SN observational properties. Results. We find that SN IMs
tend to occur in environments with lower metallicity than those of SNe IIn.
Among SNe IIn, SN IIn-L(1998S-like) SNe show higher metallicities, similar to
those of SNe IIL/P, whereas long-lasting SNe IIn (1988Z-like) show lower
metallicities, similar to those of SN IMs. The metallicity distribution of SNe
IIn can be reproduced by combining the metallicity distributions of SN IMs
(that may be produced by major outbursts of massive stars like LBVs) and SNe
IIP (produced by RSGs). The same applies to the distributions of the Normalized
Cumulative Rank (NCR) values, which quantifies the SN association to H II
regions. For SNe IIn, we find larger mass-loss rates and higher CSM velocities
at higher metallicities. The luminosity increment in the optical bands during
SN IM outbursts tend to be larger at higher metallicity, whereas the SN IM
quiescent optical luminosities tend to be lower. Conclusions. The difference in
metallicity between SNe IIn and SN IMs suggests that LBVs are only one of the
progenitor channels for SNe IIn, with 1988Z-like and 1998S-like SNe possibly
arising from LBVs and RSGs, respectively. Finally, even though linedriven winds
likely do not primarily drive the late mass-loss of CSI SN progenitors,
metallicity has some impact on the observational properties of these
transients. Key words. supernovae: general - stars: evolution - galaxies:
abundancesComment: Submitted to Astronomy and Astrophysics on 28/02/2015; submitted to
arXiv after the 1st referee repor
Critical properties and R\'enyi entropies of the spin-3/2 XXZ chain
We discuss entanglement and critical properties of the spin-3/2 XXZ chain in
its entire gapless region. Employing density-matrix renormalization group
calculations combined with different methods based on level spectroscopy,
correlation functions and entanglement entropies, we determine the sound
velocity and the Luttinger parameter of the model as a function of the
anisotropy parameter. Then, we focus on entanglement properties by
systematically studying the behavior of R\'enyi entropies under both open and
periodic boundary conditions, providing further evidence of recent findings
about entanglement entropies of excited states in conformal field theory.Comment: 8 pages, 10 figures; small text revisions and a new figure. Accepted
for publication in Phys. Rev.
No trace of a single-degenerate companion in late spectra of SNe 2011fe and 2014J
Left-over, ablated material from a possible non-degenerate companion can
reveal itself after about one year in spectra of Type Ia SNe (SNe Ia). We have
searched for such material in spectra of SN 2011fe (at 294 days after the
explosion) and for SN 2014J (315 days past explosion). The observations are
compared with numerical models simulating the expected line emission. The
spectral lines sought for are H-alpha, [O I] 6300 and [Ca II] 7291,7324, and
the expected width of these lines is about 1000 km/s. No signs of these lines
can be traced in any of the two supernovae. When systematic uncertainties are
included, the limits on hydrogen-rich ablated gas in SNe 2011fe and 2014J are
0.003 M_sun and 0.0085 M_sun, respectively, where the limit for SN 2014J is the
second lowest ever, and the limit for SN 2011fe is a revision of a previous
limit. Limits are also put on helium-rich ablated gas. These limits are used,
in conjunction with other data, to argue that these supernovae can stem from
double-degenerate systems, or from single-degenerate systems with a spun
up/spun down super-Chandrasekhar white dwarf. For SN 2011fe, other types of
hydrogen-rich donors can likely be ruled out, whereas for SN 2014J a
main-sequence donor system with large intrinsic separation is still possible.
Helium-rich donor systems cannot be ruled out for any of the two supernovae,
but the expected short delay time for such progenitors makes this possibility
less likely, especially for SN 2011fe. The broad [Ni II] 7378 emission in SN
2014J is redshifted by about +1300 km/s, as opposed to the known blueshift of
roughly -1100 km/s for SN 2011fe. [Fe II] 7155 is also redshifted in SN 2014J.
SN 2014J belongs to a minority of SNe Ia that both have a nebular redshift of
[Fe II] 7155 and [Ni II] 7378, and a slow decline of the Si II 6355 absorption
trough just after B-band maximum.Comment: 13 pages, submitted to A&
The bumpy light curve of supernova iPTF13z
A Type IIn supernova (SN) is dominated by the interaction of SN ejecta with
the circumstellar medium (CSM). Some SNe IIn (e.g., SN 2006jd) have episodes of
re-brightening ("bumps") in their light curves. We present iPTF13z, a SN IIn
discovered by the intermediate Palomar Transient Factory (iPTF) and
characterised by several bumps in its light curve. We analyse this peculiar
behaviour trying to infer the properties of the CSM and of the SN explosion, as
well as the nature of its progenitor star. We obtained multi-band optical
photometry for over 1000 days after discovery with the P48 and P60 telescopes
at Palomar Observatory. We obtained low-resolution optical spectra in the same
period. We did an archival search for progenitor outbursts. We analyse our
photometry and spectra, and compare iPTF13z to other SNe IIn. A simple
analytical model is used to estimate properties of the CSM. iPTF13z was a SN
IIn showing a light curve with five bumps during its decline phase. The bumps
had amplitudes between 0.4 and 0.9 mag and durations between 20 and 120 days.
The most prominent bumps appeared in all our different optical bands. The
spectra showed typical SN IIn characteristics, with emission lines of H
(with broad component FWHM ~ and narrow
component FWHM ~) and He I, but also with Fe II, Ca II,
Na I D and H P-Cygni profiles (with velocities of ~ ). A pre-explosion outburst was identified lasting days,
with mag around 210 days before discovery. Large, variable
progenitor mass-loss rates (~> 0.01 ) and CSM densities
(~> 10 g cm) are derived. We suggest that the light curve bumps
of iPTF13z arose from SN ejecta interacting with denser regions in the CSM,
possibly produced by the eruptions of a luminous blue variable star.Comment: Version 2: Update to match published paper. 21 pages, 14 figures,
abstract abridged to comply with arXiv length limit. In version 1 of the
paper on arXiv, Table 3 had some erroneous entries. Table 3 is now corrected
and available via VizieR. Version 1 comment: Accepted for publication in
Astronomy & Astrophysics (24 pages, 14 figures, abstract abridged by 20 % not
to exceed the arXiv length limit
The peculiar Type Ia supernova iPTF14atg: Chandrasekhar-mass explosion or violent merger?
iPTF14atg, a subluminous peculiar Type Ia supernova (SN Ia) similar to SN
2002es, is the first SN Ia for which a strong UV flash was observed in the
early-time light curves. This has been interpreted as evidence for a
single-degenerate (SD) progenitor system where such a signal is expected from
interactions between the SN ejecta and the non-degenerate companion star. Here,
we compare synthetic observables of multi-dimensional state-of-the-art
explosion models for different progenitor scenarios to the light curves and
spectra of iPTF14atg. From our models, we have difficulties explaining the
spectral evolution of iPTF14atg within the SD progenitor channel. In contrast,
we find that a violent merger of two carbon-oxygen white dwarfs with 0.9 and
0.76 solar masses, respectively, provides an excellent match to the spectral
evolution of iPTF14atg from 10d before to several weeks after maximum light.
Our merger model does not naturally explain the initial UV flash of iPTF14atg.
We discuss several possibilities like interactions of the SN ejecta with the
circum-stellar medium and surface radioactivity from a He ignited merger that
may be able to account for the early UV emission in violent merger models.Comment: 12 pages, 7 figures, accepted for publication in MNRA
The Carnegie Supernova Project I: methods to estimate host-galaxy reddening of stripped-envelope supernovae
We aim to improve upon contemporary methods to estimate host-galaxy reddening
of stripped-envelope (SE) supernovae (SNe). To this end the Carnegie Supernova
Project (CSP-I) SE SNe photometry data release, consisting of nearly three
dozen objects, is used to identify a minimally reddened sub-sample for each
traditionally defined spectroscopic sub-types (i.e, SNe~IIb, SNe~Ib, SNe~Ic).
Inspection of the optical and near-infrared (NIR) colors and color evolution of
the minimally reddened sub-samples reveals a high degree of homogeneity,
particularly between 0d to +20d relative to B-band maximum. This motivated the
construction of intrinsic color-curve templates, which when compared to the
colors of reddened SE SNe, yields an entire suite of optical and NIR color
excess measurements. Comparison of optical/optical vs. optical/NIR color excess
measurements indicates the majority of the CSP-I SE SNe suffer relatively low
amounts of reddening and we find evidence for different R_(V)^(host) values
among different SE SN. Fitting the color excess measurements of the seven most
reddened objects with the Fitzpatrick (1999) reddening law model provides
robust estimates of the host visual-extinction A_(V)^(host) and R_(V)^(host).
In the case of the SE SNe with relatively low amounts of reddening, a preferred
value of R_(V)^(host) is adopted for each sub-type, resulting in estimates of
A_(V)^(host) through Fitzpatrick (1999) reddening law model fits to the
observed color excess measurements. Our analysis suggests SE SNe reside in
galaxies characterized by a range of dust properties. We also find evidence SNe
Ic are more likely to occur in regions characterized by larger R_(V)^(host)
values compared to SNe IIb/Ib and they also tend to suffer more extinction.
These findings are consistent with work in the literature suggesting SNe Ic
tend to occur in regions of on-going star formation.Comment: Abstract abridged to fit allowed limit. Resubmitted to A&A, 34 pages,
19 figures, 6 tables. Constructive comments welcome
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