419 research outputs found
Constraints on explosive silicon burning in core-collapse supernovae from measured Ni/Fe ratios
Measurements of explosive nucleosynthesis yields in core-collapse supernovae
provide tests for explosion models. We investigate constraints on explosive
conditions derivable from measured amounts of nickel and iron after radioactive
decays using nucleosynthesis networks with parameterized thermodynamic
trajectories. The Ni/Fe ratio is for most regimes dominated by the production
ratio of 58Ni/(54Fe + 56Ni), which tends to grow with higher neutron excess and
with higher entropy. For SN 2012ec, a supernova that produced a Ni/Fe ratio of
times solar, we find that burning of a fuel with neutron excess
is required. Unless the progenitor metallicity
is over 5 times solar, the only layer in the progenitor with such a neutron
excess is the silicon shell. Supernovae producing large amounts of stable
nickel thus suggest that this deep-lying layer can be, at least partially,
ejected in the explosion. We find that common spherically symmetric models of
Msun stars exploding with a delay time of less than
one second ( Msun) are able to achieve such silicon-shell
ejection. Supernovae that produce solar or sub-solar Ni/Fe ratios, such as SN
1987A, must instead have burnt and ejected only oxygen-shell material, which
allows a lower limit to the mass cut to be set. Finally, we find that the
extreme Ni/Fe value of 60-75 times solar derived for the Crab cannot be
reproduced by any realistic-entropy burning outside the iron core, and
neutrino-neutronization obtained in electron-capture models remains the only
viable explanation.Comment: 13 pages, 9 figures, accepted for publication in Ap
Supernova 1996cr: SN 1987A's Wild Cousin?
We report on new VLT optical spectroscopic and multi-wavelength archival
observations of SN1996cr, a previously identified ULX known as Circinus Galaxy
X-2. Our optical spectrum confirms SN1996cr as a bona fide type IIn SN, while
archival imaging isolates its explosion date to between 1995-02-28 and
1996-03-16. SN1996cr is one of the closest SNe (~3.8 Mpc) in the last several
decades and in terms of flux ranks among the brightest radio and X-ray SNe ever
detected. The wealth of optical, X-ray, and radio observations that exist for
this source provide relatively detailed constraints on its post-explosion
expansion and progenitor history, including an preliminary angular size
constaint from VLBI. The archival X-ray and radio data imply that the
progenitor of SN1996cr evacuated a large cavity just prior to exploding: the
blast wave likely expanded for ~1-2 yrs before eventually striking the dense
circumstellar material which surrounds SN1996cr. The X-ray and radio emission,
which trace the progenitor mass-loss rate, have respectively risen by a factor
of ~2 and remained roughly constant over the past 7 yr. This behavior is
reminiscent of the late rise of SN1987A, but 1000 times more luminous and much
more rapid to onset. Complex Oxygen line emission in the optical spectrum
further hints at a possible concentric shell or ring-like structure. The
discovery of SN1996cr suggests that a substantial fraction of the closest SNe
observed in the last several decades have occurred in wind-blown bubbles. An
Interplanetary Network position allows us to reject a tentative GRB association
with BATSE 4B960202. [Abridged]Comment: 25 pages with tables, 12 figures (color), accepted to ApJ, comments
welcome; v2 - updated to reflect the subsequent rejection of our tentative
GRB association based on a revised error region from the Interplanetary
Network (thanks to Kevin Hurley) and include a few additional references; v3
- corrected some errors in Tables 7 and
Mass limits for the progenitor star of supernova 2001du and other type II-P supernovae
The supernova SN2001du in the galaxy NGC1365 (19+/-2Mpc), is a core-collapse
event of type II-P. Images of this galaxy, have been taken with HST
approximately 6.6 years before discovery and include the supernova position on
the WFPC2 field of view. We have observed the supernova with the WFPC2 to allow
accurate differential astrometry of SN2001du on the pre-explosion frames. There
is a marginal detection (3-sigma) of a source close to the supernova position
on the prediscovery V-band frame, however it is not precisely coincident and we
do not believe it to be a robust detection of a point source. We conclude that
there is no stellar progenitor at the supernova position and derive sensitivity
limits of the prediscovery images which provide an upper mass limit for the
progenitor star. We estimate that the progenitor had a mass of less than
15M_sol. We revisit two other nearby SNe II-P which have high quality
pre-explosion images, and refine the upper mass limits for the progenitor
stars. Finally we compile all the direct information available for the
progenitors of eight nearby core-collapse supernovae and compare their mass
estimates. These are compared with the latest stellar evolutionary models of
pre-supernova evolution which have attempted to relate metallicity and mass to
the supernovae type. Reasonable agreement is found for the lower mass events
(generally the II-P), but some discrepancies appear at higher masses.
(abridged).Comment: Minor changes, accepted for publication in MNRAS, full resolution
version on http://www.ast.cam.ac.uk/~sjs/papers/sn2001du_smartt.p
Detection of a red supergiant progenitor star of a type II-plateau supernova
We present the discovery of a red supergiant star that exploded as supernova
2003gd in the nearby spiral galaxy M74. The Hubble Space Telescope (HST) and
the Gemini Telescope imaged this galaxy 6 to 9 months before the supernova
explosion and subsequent HST images confirm the positional coincidence of the
supernova with a single,resolved star which is an 8 +4/-2 solar mass red
supergiant. This confirms both stellar evolution models and supernova theories
which predict that type II-Plateau supernovae have cool red supergiants as
their immediate progenitor stars.Comment: Accepted for publication in Science, supporting online material
available at http://www.ast.cam.ac.uk/~sjs/sn2003gd
Supernova 2012ec: Identification of the progenitor and early monitoring with PESSTO
We present the identification of the progenitor of the Type IIP SN 2012ec in
archival pre-explosion HST WFPC2 and ACS/WFC F814W images. The properties of
the progenitor are further constrained by non-detections in pre-explosion WFPC2
F450W and F606W images. We report a series of early photometric and
spectroscopic observations of SN 2012ec. The r'-band light curve shows a
plateau with M(r')=-17.0. The early spectrum is similar to the Type IIP SN
1999em, with the expansion velocity measured at Halpha absorption minimum of
-11,700 km/s (at 1 day post-discovery). The photometric and spectroscopic
evolution of SN 2012ec shows it to be a Type IIP SN, discovered only a few days
post-explosion (<6d). We derive a luminosity for the progenitor, in comparison
with MARCS model SEDs, of log L/Lsun = 5.15+/-0.19, from which we infer an
initial mass range of 14-22Msun. This is the first SN with an identified
progenitor to be followed by the Public ESO Spectroscopic Survey of Transient
Objects (PESSTO).Comment: 6 pages, 3 figures, MNRAS accepte
A Study of the Type II-P Supernova 2003gd in M74
We present photometric and spectroscopic data of the type II-P supernova
2003gd, which was discovered in M74 close to the end of its plateau phase. SN
2003gd is the first type II supernova to have a directly confirmed red
supergiant progenitor. We compare SN 2003gd with SN 1999em, a similar type II-P
supernova, and estimate an explosion date of 18th March 2003. We determine a
reddening towards the supernova of E(B-V) = 0.14+/-0.06, using three different
methods. We also calculate three new distances to M74 of 9.6+/-2.8 Mpc,
7.7+/-1.7 Mpc and 9.6+/-2.2 Mpc. The former was estimated using the
Standardised Candle Method (SCM), for type II supernovae, and the latter two
using the Brightest Supergiants Method (BSM). When combined with existing
kinematic and BSM distance estimates, we derive a mean value of 9.3+/-1.8 Mpc.
SN 2003gd was found to have a lower tail luminosity compared to other
``normal'' type II-P SNe bringing into question the nature of this supernova.
We present a discussion concluding that this is a ``normal'' type II-P
supernova which is consistent with the observed progenitor mass of 8(+4/-2) Mo.Comment: 23 pages, 24 figures to appear in MNRA
Supernovae from rotating stars
The present paper discusses the main physical effects produced by stellar
rotation on presupernovae, as well as observations which confirm these effects
and their consequences for presupernova models. Rotation critically influences
the mass of the exploding cores, the mass and chemical composition of the
envelopes and the types of supernovae, as well as the properties of the
remnants and the chemical yields. In the formation of gamma-ray bursts,
rotation and the properties of rotating stars appear as the key factor. In
binaries, the interaction between axial rotation and tidal effects often leads
to interesting and unexpected results. Rotation plays a key role in shaping the
evolution and nucleosynthesis in massive stars with very low metallicities
(metallicity below about the Small Magellanic Cloud metallicity down to
Population III stars). At solar and higher metallicities, the effects of
rotation compete with those of stellar winds. In close binaries, the
synchronisation process can lock the star at a high rotation rate despite
strong mass loss and thus both effects, rotation and stellar winds, have a
strong impact. In conclusion, rotation is a key physical ingredient of the
stellar models and of presupernova stages, and the evolution both of single
stars and close binaries. Moreover, important effects are expected along the
whole cosmic history.Comment: 36 pages, 15 figures, published in Handbook of Supernovae, A.W.
Alsabti and P. Murdin (eds), Springe
Constraining the physical properties of Type II-P supernovae using nebular phase spectra
We present a study of the nebular phase spectra of a sample of Type
II-Plateau supernovae with identified progenitors or restrictive limits. The
evolution of line fluxes, shapes, and velocities are compared within the
sample, and interpreted by the use of a spectral synthesis code. The small
diversity within the dataset can be explained by strong mixing occurring during
the explosion, and by recognising that most lines have significant
contributions from primordial metals in the H envelope, which dominates the
total ejecta mass in these type of objects. In particular, when using the [O I]
6300, 6364 Angstrom doublet for estimating the core mass of the star, care has
to be taken to account for emission from primordial O in the envelope. Finally,
a correlation between the H-alpha line width and the mass of 56Ni is presented,
suggesting that higher energy explosions are associated with higher 56Ni
production.Comment: 18 pages, 15 figures, accepted for publication in MNRA
Faint Supernovae and Supernova Impostors: Case studies of SN2002kg/NGC2403-V37 and SN 2003gm
Photometric and spectroscopic observations of the faint Supernovae (SNe)
2002kg and 2003gm, and their precursors, in NGC 2403 and NGC 5334 respectively,
are presented. The properties of these SNe are discussed in the context of
previously proposed scenarios for faint SNe: low mass progenitors producing
under-energetic SNe; SNe with ejecta constrained by a circumstellar medium; and
outbursts of massive Luminous Blue Variables (LBVs). The last scenario has been
referred to as ``Type V SNe'', ``SN impostors'' or ``fake SNe.'' The faint SN
2002kg reached a maximum brightness of , much fainter than
normal type II SNe. The precursor of SN 2002kg is confirmed to be, as shown in
previous work, the LBV NGC2403-V37. Strong lines are observed
in the spectra of SN 2002kg, similar to both the LBV NGC2363-V1 and the type
IIn SN 1995G. The spectrum of SN 2002kg does show strong resolved at 6549,6583\ang. The identified progenitor of SN 2003gm
is a bright yellow star, consistent with a F5-G2 supergiant. SN 2003gm, at the
epoch of discovery, was of similar brightness to the possible fake SN 1997bs.
Photometrically SN 2003gm shows the same decrease in brightness, over the same
time period as SN 1997bs. The early time spectra of SN 2003gm are dominated by
Balmer emission lines, which at the observed resolution, appear similar to SN
2000ch. On the basis of the post-discovery photometric and spectroscopic
observations presented here we suggest that SN 2003gm is a similar event to SN
1997bs. The presence of strong lines, near
, is suggested as a possible means of identifying objects
such as SN 2002kg/NGC2403-V37 as being LBVs - although not as a general
classification criterion of all LBVs masquerading as SNe (abridged).Comment: 17 pages, 17 figures (4 jpg), MNRAS accepted, 4 typos correcte
PESSTO monitoring of SN 2012hn: further heterogeneity among faint type I supernovae
We present optical and infrared monitoring data of SN 2012hn collected by the
Public ESO Spectroscopic Survey for Transient Objects (PESSTO). We show that SN
2012hn has a faint peak magnitude (MR ~ -15.7) and shows no hydrogen and no
clear evidence for helium in its spectral evolution. Instead, we detect
prominent Ca II lines at all epochs, which relates this transient to previously
described 'Ca-rich' or 'gap' transients. However, the photospheric spectra
(from -3 to +32 d with respect to peak) of SN 2012hn show a series of
absorption lines which are unique, and a red continuum that is likely intrinsic
rather than due to extinction. Lines of Ti II and Cr II are visible. This may
be a temperature effect, which could also explain the red photospheric colour.
A nebular spectrum at +150d shows prominent CaII, OI, CI and possibly MgI lines
which appear similar in strength to those displayed by core-collapse SNe. To
add to the puzzle, SN 2012hn is located at a projected distance of 6 kpc from
an E/S0 host and is not close to any obvious starforming region. Overall SN
2012hn resembles a group of faint H-poor SNe that have been discovered recently
and for which a convincing and consistent physical explanation is still
missing. They all appear to explode preferentially in remote locations offset
from a massive host galaxy with deep limits on any dwarf host galaxies,
favouring old progenitor systems. SN 2012hn adds heterogeneity to this sample
of objects. We discuss potential explosion channels including He-shell
detonations and double detonations of white dwarfs as well as peculiar
core-collapse SNe.Comment: 14 pages, 14 figures, accepted to MNRAS on 14/10/201
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