941 research outputs found
XMM-Newton detects the beginning of the X-ray decline of SN 1995N
We present the results of a new XMM-Newton observation of the interacting
supernova 1995N, performed on July 27, 2003. We find that the 0.2-10.0 keV flux
has dropt at a level of 1.44e-13 erg cm^-2 s^-1, about one order of magnitude
lower than that of a previous ASCA observation performed on January 1998. The
X-ray spectral analysis shows statistically significant evidence for the
presence of two distinct components, that can be modeled with emission from
optically thin, thermal plasmas at different temperatures. From these
temperatures we derive that the exponent of the ejecta density distribution is
n ~ 6.5.Comment: 3 pages, 2 figures. To appear in proceedings of the International
Conference "1604-2004: Supernovae as Cosmological Lighthouses" (Padova,
Italy, June 16-19, 2004), eds. M. Turatto, W. Shea, S. Benetti and L.
Zampieri, ASP conference Serie
Supernova Impostors and other Gap Transients
Besides supernovae, few astrophysical processes can release close to 10^51
erg of energy. A growing number of stellar outbursts are now recognised to have
energy releases matching those of faint supernovae. These transients can be
triggered by a variety of mechanisms, and their discrimination is sometimes a
tricky issue.Comment: Authors version of invited Comment Article published as part of a
Supernova Focus Issue in Nature Astronomy, 5 pages, 2 figure
Ejecta and progenitor of the low-luminosity Type IIP supernova 2003Z
The origin of low-luminosity Type IIP supernovae is unclear: they have been
proposed to originate either from massive (about 25 Msun) or low-mass (about 9
Msun) stars. We wish to determine parameters of the low-luminosity Type IIP
supernova 2003Z, to estimate a mass-loss rate of the presupernova, and to
recover a progenitor mass. We compute the hydrodynamic models of the supernova
to describe the light curves and the observed expansion velocities. The wind
density of the presupernova is estimated using a thin shell model for the
interaction with circumstellar matter. We estimate an ejecta mass of 14 Msun,
an explosion energy of 2.45x10^50 erg, a presupernova radius of 229 Rsun, and a
radioactive Ni-56 amount of 0.0063 Msun. The upper limit of the wind density
parameter in the presupernova vicinity is 10^13 g/cm, and the mass lost at the
red/yellow supergiant stage is less than 0.6 Msun assuming the constant
mass-loss rate. The estimated progenitor mass is in the range of 14.4-17.4
Msun. The presupernova of SN 2003Z was probably a yellow supergiant at the time
of the explosion. The progenitor mass of SN 2003Z is lower than those of SN
1987A and SN 1999em, normal Type IIP supernovae, but higher than the lower
limit of stars undergoing a core collapse. We propose an observational test
based on the circumstellar interaction to discriminate between the massive
(about 25 Msun) and moderate-mass (about 16 Msun) scenarios.Comment: 8 pages, 9 figures, 3 tables, accepted for publication in Astronomy &
Astrophysics; one reference remove
Massive stars exploding in a He-rich circumstellar medium - I. Type Ibn (SN 2006jc-like) events
We present new spectroscopic and photometric data of the Type Ibn supernovae 2006jc, 2000er and 2002ao. We discuss the general properties of this recently proposed supernova family, which also includes SN 1999cq. The early-time monitoring of SN 2000er traces the evolution of this class of objects during the first few days after the shock breakout. An overall similarity in the photometric and spectroscopic evolution is found among the members of this group, which would be unexpected if the energy in these core-collapse events was dominated by the interaction between supernova ejecta and circumstellar medium. Type Ibn supernovae appear to be rather normal Type Ib/c supernova explosions which occur within a He-rich circumstellar environment. SNe Ibn are therefore likely produced by the explosion of Wolf–Rayet progenitors still embedded in the He-rich material lost by the star in recent mass-loss
episodes, which resemble known luminous blue variable eruptions. The evolved Wolf–Rayet star could either result from the evolution of a very massive star or be the more evolved member of a massive binary system.We also suggest that there are a number of arguments in favour of a Type Ibn classification for the historical SN 1885A (S-Andromedae), previously considered as an anomalous Type Ia event with some resemblance to SN 1991bg
A very faint core-collapse supernova in M85
An anomalous transient in the early Hubble-type (S0) galaxy Messier 85 (M85)
in the Virgo cluster was discovered by Kulkarni et al. (2007) on 7 January 2006
that had very low luminosity (peak absolute R-band magnitude MR of about -12)
that was constant over more than 80 days, red colour and narrow spectral lines,
which seem inconsistent with those observed in any known class of transient
events. Kulkarni et al. (2007) suggest an exotic stellar merger as the possible
origin. An alternative explanation is that the transient in M85 was a type
II-plateau supernova of extremely low luminosity, exploding in a lenticular
galaxy with residual star-forming activity. This intriguing transient might be
the faintest supernova that has ever been discovered.Comment: 7 pages, 2 figures. Submitted to Nature "Brief Communication Arising"
on 18 July 2007, Accepted on 17 August 2007. Arising from: Kulkarni et al.
2007, Nature, 447, 458-46
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
Evidence of Asymmetry in SN 2007rt, a Type IIn Supernova
An optical photometric and spectroscopic analysis of the slowly-evolving Type
IIn SN2007rt is presented, covering a duration of 481 days after discovery. Its
earliest spectrum, taken approximately 100 days after the explosion epoch,
indicates the presence of a dense circumstellar medium, with which the
supernova ejecta is interacting. This is supported by the slowly-evolving light
curve. A notable feature in the spectrum of SN 2007rt is the presence of a
broad He I 5875 line, not usually detected in Type IIn supernovae. This may
imply that the progenitor star has a high He/H ratio, having shed a significant
portion of its hydrogen shell via mass-loss. An intermediate resolution
spectrum reveals a narrow Halpha P-Cygni profile, the absorption component of
which has a width of 128 km/s. This slow velocity suggests that the progenitor
of SN 2007rt recently underwent mass-loss with wind speeds comparable to the
lower limits of those detected in luminous blue variables. Asymmetries in the
line profiles of H and He at early phases bears some resemblance to
double-peaked features observed in a number of Ib/c spectra. These asymmetries
may be indicative of an asymmetric or bipolar outflow or alternatively dust
formation in the fast expanding ejecta. In addition, the late time spectrum, at
over 240 days post-explosion, shows clear evidence for the presence of newly
formed dust.Comment: Submitted to A&A on 4/2/2009. Accepted by A&A on 17/5/2009.15 pages
plus 3 pages of online materia
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