19 research outputs found
Probing supernovae ejecta by Halpha damping wings
It is predicted that H emission line at the early nebular epoch of
type II-P supernovae may display robust observational effects of damping wings.
This is illustrated by Monte-Carlo simulations. The strength of damping wing
effects may be used to constrain parameters of the line-emitting zone. An
anomalous redshift, width and red wing of H revealed by SN 1997D on day
150 are explained in terms of damping wing effects.Comment: 8 pages, 2 figure
Moderate Asphericity of the SN 2002ic Circumstellar Envelope
The polarization of SN 2002ic interacting with a dense circumstellar envelope
is calculated in the context of the asymmetric version of a previously proposed
spherical interaction model. The circumstellar envelope is taken to be oblate.
The observed polarization (Wang et al. 2004) can be reproduced for an aspect
ratio of 0.65-0.7 assuming inclination angles >60 degrees. This model predicts
a weak sensitivity of the line profiles to the orientation, in agreement with
the absence of significant variations of the line profiles among SN 2002ic-like
supernovae. We propose a test for distinguishing between the binary and single
star progenitor scenarios based upon the polarization distribution function for
the growing sample of these events.Comment: 13 pages, 4 figs., ApJ, accepte
Optical Signatures of Circumstellar Interaction in Type IIP Supernovae
We propose new diagnostics for circumstellar interaction in Type IIP
supernovae by the detection of high velocity (HV) absorption features in Halpha
and He I 10830 A lines during the photospheric stage. To demonstrate the
method, we compute the ionization and excitation of H and He in supernova
ejecta taking into account time-dependent effects and X-ray irradiation. We
find that the interaction with a typical red supergiant wind should result in
the enhanced excitation of the outer layers of unshocked ejecta and the
emergence of corresponding HV absorption, i.e. a depression in the blue
absorption wing of Halpha and a pronounced absorption of He I 10830 A at a
radial velocity of about -10,000 km/s. We identify HV absorption in Halpha and
He I 10830 A lines of SN 1999em and in Halpha of SN 2004dj as being due to this
effect. The derived mass loss rate is close to 10^{-6} Msun/yr for both
supernovae, assuming a wind velocity 10 km/s. We argue that, in addition to the
HV absorption formed in the unshocked ejecta, spectra of SN 2004dj and SN
1999em show a HV notch feature that is formed in the cool dense shell (CDS)
modified by the Rayleigh-Taylor instability. The CDS results from both shock
breakout and radiative cooling of gas that has passed through the reverse shock
wave. The notch becomes dominant in the HV absorption during the late
photospheric phase, ~60 d. The wind density deduced from the velocity of the
CDS is consistent with the wind density found from the HV absorption produced
by unshocked ejecta.Comment: 38 pages, 12 figures, ApJ, in pres
Late Emission from the Type Ib/c SN 2001em: Overtaking the Hydrogen Envelope
The Type Ib/c supernova SN 2001em was observed to have strong radio, X-ray,
and Halpha emission at an age of about 2.5 yr. Although the radio and X-ray
emission have been attributed to an off-axis gamma-ray burst, we model the
emission as the interaction of normal SN Ib/c ejecta with a dense, massive (3
Msun) circumstellar shell at a distance about 7 x 10^{16} cm. We investigate
two models, in which the circumstellar shell has or has not been overtaken by
the forward shock at the time of the X-ray observation. The circumstellar shell
was presumably formed by vigorous mass loss with a rate (2-10) x 10^{-3}
Msun/yr at 1000-2000 yr prior to the supernova explosion. The hydrogen envelope
was completely lost, and subsequently was swept up and accelerated by the fast
wind of the presupernova star up to a velocity of 30-50 km/s. Although
interaction with the shell can explain most of the late emission properties of
SN 2001em, we need to invoke clumping of the gas to explain the low absorption
at X-ray and radio wavelengths.Comment: 26 pages, 4 figures, ApJ submitte
The spectacular evolution of Supernova 1996al over 15 years: a low energy explosion of a stripped massive star in a highly structured environment
Spectrophotometry of SN 1996al carried out throughout 15 years is presented.
The early photometry suggests that SN 1996al is a Linear type-II supernova,
with an absolute peak of Mv ~ -18.2 mag. Early spectra present broad,
asymmetric Balmer emissions, with super-imposed narrow lines with P-Cygni
profile, and He I features with asymmetric, broad emission components. The
analysis of the line profiles shows that the H and He broad components form in
the same region of the ejecta. By day +142, the Halpha profile dramatically
changes: the narrow P-Cygni profile disappears, and the Halpha is fitted by
three emission components, that will be detected over the remaining 15 yrs of
the SN monitoring campaign. Instead, the He I emissions become progressively
narrower and symmetric. A sudden increase in flux of all He I lines is observed
between 300 and 600 days. Models show that the supernova luminosity is
sustained by the interaction of low mass (~1.15 Msun) ejecta, expelled in a low
kinetic energy (~ 1.6 x 10^50 erg) explosion, with highly asymmetric
circumstellar medium. The detection of Halpha emission in pre-explosion archive
images suggests that the progenitor was most likely a massive star (~25 Msun
ZAMS) that had lost a large fraction of its hydrogen envelope before explosion,
and was hence embedded in a H-rich cocoon. The low-mass ejecta and modest
kinetic energy of the explosion are explained with massive fallback of material
into the compact remnant, a 7-8 Msun black hole.Comment: 27 pages, 23 figures, Accepted for publication in MNRA
The type IIn supernova 1994W: evidence for the explosive ejection of a circumstellar envelope
We present and analyse spectra of the Type IIn supernova 1994W obtained
between 18 and 203 days after explosion. During the luminous phase (first 100
d) the line profiles are composed of three major components: (i) narrow P-Cygni
lines with the absorption minima at -700 km/s; (ii) broad emission lines with
BVZI ~4000 km/s; and (iii) broad, smooth wings, most apparent in H-alpha. These
components are identified with an expanding circumstellar (CS) envelope,
shocked cool gas in the forward post-shock region, and multiple Thomson
scattering in the CS envelope, respectively. The absence of broad P-Cygni lines
from the supernova is the result of the formation of an optically thick, cool,
dense shell at the interface of the ejecta and the CS envelope. We model the
supernova deceleration and Thomson scattering wings to recover the density,
radial extent and Thomson optical depth of the CS envelope during the first
month. We reproduce the light curve with a hydrodynamical model and find it to
be powered by a combination of internal energy leakage after the explosion of
an extended pre-supernova (~10^15 cm) and luminosity from circumstellar
interaction. We recover the pre-explosion kinematics of the CS envelope: it is
close to homologous expansion with outer velocity ~1100 km/s and a kinematic
age of ~1.5 yr. The CS envelope's high mass and kinetic energy, combined with
its small age, strongly suggest that the CS envelope was explosively ejected
about 1.5 yr before the supernova explosion.Comment: 22 pages, 21 figures. Accepted for publication in Monthly Notices of
the Royal Astronomical Societ
Chandra Observations of Type Ia Supernovae: Upper Limits to the X-ray Flux of SN 2002bo, SN 2002ic, SN 2005gj, and SN 2005ke
We set sensitive upper limits to the X-ray emission of four Type Ia
supernovae (SNe Ia) using the Chandra X-ray Observatory. SN 2002bo, a normal,
although reddened, nearby SN Ia, was observed 9.3 days after explosion. For an
absorbed, high temperature bremsstrahlung model the flux limits are 3.2E-16
ergs/cm^2/s (0.5-2 keV band) and 4.1E-15 ergs/cm^2/s (2-10 keV band). Using
conservative model assumptions and a 10 km/s wind speed, we derive a mass loss
rate of \dot{M} ~ 2E-5 M_\odot/yr, which is comparable to limits set by the
non-detection of Halpha lines from other SNe Ia. Two other objects, SN 2002ic
and SN 2005gj, observed 260 and 80 days after explosion, respectively, are the
only SNe Ia showing evidence for circumstellar interaction. The SN 2002ic X-ray
flux upper limits are ~4 times below predictions of the interaction model
currently favored to explain the bright optical emission. To resolve this
discrepancy we invoke the mixing of cool dense ejecta fragments into the
forward shock region, which produces increased X-ray absorption. A modest
amount of mixing allows us to accommodate the Chandra upper limit. SN 2005gj is
less well studied at this time. Assuming the same circumstellar environment as
for SN 2002i, the X-ray flux upper limits for SN 2005gj are ~4 times below the
predictions, suggesting that mixing of cool ejecta into the forward shock has
also occurred here. Our reanalysis of Swift and Chandra data on SN 2005ke does
not confirm a previously reported X-ray detection. The host galaxies NGC 3190
(SN 2002bo) and NGC 1371 (SN 2005ke) each harbor a low luminosity (L_X ~ 3-4E40
ergs/s) active nucleus in addition to wide-spread diffuse soft X-ray emission.Comment: 16 pages, to appear in ApJ (20 Nov 2007