67 research outputs found
Broad Band Polarimetry of Supernovae: SN1994D, SN1994Y, SN1994ae, SN1995D and SN 1995H
We have made polarimetric observations of three Type Ia supernovae (SN Ia)
and two type II supernovae (SN II). No significant polarization was detected
for any of the SN Ia down to the level of 0.2\%, while polarization of order
was detected for the two SN II 1994Y and 1995H. A catalog of all the
SNe with polarization data is compiled that shows a distinct trend that all the
5 SN II with sufficient polarimetric data show polarizations at about 1\%,
while none of the 9 SN Ia in the sample show intrinsic polarization. This
systematic difference in polarization of supernovae, if confirmed, raises many
interesting questions concerning the mechanisms leading to supernova
explosions. Our observations enhance the use of SN Ia as tools for determining
the distance scale through various techniques, but suggest that one must be
very cautious in utilizing Type II for distance determinations. However, we
caution that the link between the asphericity of a supernova and the measured
``intrinsic'' polarization is complicated by reflected light from the
circumstellar material and the intervening interstellar material, the so-called
light echo. This effect may contribute more substantially to SN II than to SN
Ia. The tight limits on polarization of SN Ia may constrain progenitor models
with extensive scattering nebulae such as symbiotic stars and other systems of
extensive mass loss.Comment: 27 pages, 3 Postscript figure
The Ultimate Light Curve of SN 1998bw/GRB 980425
We present multicolor light curves of SN 1998bw which appeared in ESO184-G82
in close temporal and spacial association with GRB 980425. They are based on
observations done at Cerro Tololo Inter-American Observatory and data from the
literature. The CTIO photometry reaches ~86 days after the GRB in and ~160
days after the GRB in BV(RI)_C. The observations in U extend by about 30 days
the previously known coverage, and determine the slope of the early exponential
tail.
We calibrate a large set of local standards in common with those of previous
studies and use them to transform published observations of the SN to our
realization of the standard photometric system. We show that the photometry
from different sources merges smoothly and provide a unified set of 300
observations of the SN in five bands. Using the extensive set of spectra in
public domain we compute extinction and K corrections, and build
quasi-bolometric unreddened rest frame light curves. We provide low degree
piecewise spline fits to these light curves with daily sampling. They reach ~86
rest frame days after the GRB with U band coverage, and ~498 rest frame days
after the GRB without U.Comment: 38 pages, 5 figures, 3 table
Estudios polarimétricos de nebulosas de reflexión
Se presentan observaciones UBVRI de objetos selectos, inmersos en nebulosas de reflexión, hechas con el fotopolarÃmetro de la UNLP y el telescopio "Perrine" del Observatorio Félix Aguilar. Se estudia la relación geométrica entre las caracterÃsticas filamentarias de la estructura y la dirección del campo magnético asà como las dependencia con la longitud de onda de la polarización lineal. Cuatro de los objetos estudiados presentan valores anómalos de la longitud de onda de máxima polarización.Asociación Argentina de AstronomÃ
Numerical test of the stokes parameters
We made a numerical test of the estimators of the Stokes parameters. We tested the most common estimators in literature plus a maximum likelihood solution. We make an statistical analysis to compare the true errors with the observed ones and to determine the efficiency of the estimators. The maximum likelihood solution works fine under the conditions of the model when the errors are comparatively large.Asociación Argentina de AstronomÃ
Expansion model for the external envelopes of the SN 1987A
Assuming the existence of a polarization produced by Thompson scattering, as suggested by the observations, a model has been computed for the optically thin layers of SN 1987A. Supposing that the isodensities in this region are oblate ellipsoids, we found the equation that describes the observable polarization as a function of its parameters. If we assumed that the inclination of the axis of symmetry and the eccentricity of the envelope are constant and using a model for the mass ejection, we were able to study the evolution of the size and density of the region as a function of time.Asociación Argentina de AstronomÃ
The Luminous Type Ic SN 1992ar at z=0.145
We present spectroscopic and photometric observations of SN1992ar, the more
distant SN in the Calan/Tololo Survey. We compare its spectrum with those of
nearby Type Ia and Ic SNe and conclude that the latter type is a better match
to SN 1992ar. Using K-corrections based on the spectra of well observed Type Ic
and Ia SNe we compute different possible rest frame light curves of SN 1992ar
and compare them with those of representative SNe of each type observed in the
nearby universe. From the photometry and the spectra, we are able to conclude
that SN 1992ar cannot be matched by any known example of a Type Ia SN. Even
though the data set collected is fairly complete (one spectrum and 10
photometric points), it is not possible to decide whether SN 1992ar was a fast
Type Ic SN, like SN 1994I, or a slow one, like SN 1983V. The absolute V
magnitudes at maximum implied by each of these possibilities are -19.2 and
-20.2, respectively. The latter would make SN 1992ar one of the brightest SNe
on record. SN 1992ar, hence, illustrates the problem of contamination faced by
the high z Type Ia SNe samples whose luminosity distances are used to determine
the cosmological parameters of the Universe. We present observational criteria
to distinguish the two SN types when the SiII 6355 line is redshifted out of
the sensitivity range of typical CCD detectors, and discuss the effect that
these luminous Type Ic SNe would have on the measured cosmological parameters,
if not removed from the High-z Type Ia SN samples.Comment: 40 pages, 9 figures. Accepted for publication in Astrophysical
Journa
The Early Asymmetries of Supernova 2008D / XRF 080109
Spectropolarimetry of the Type Ib SN 2008D, associated with the XRF 080109,
at two separate epochs, are presented. The epochs of these observations
correspond to V-band light curve maximum and 15 days after light curve maximum
(or 21 and 36 days after the XRF). We find SN 2008D to be significantly
polarized, although the largest contribution is due to the interstellar
polarization component of Q_ISP=0+/-0.1% and U_ISP=-1.2+/-0.1%. At the two
epochs, the spectropolarimetry of SN 2008D is classified as being
D1+L(HeI)+L(Ca II). The intrinsic polarization of continuum wavelength regions
is <0.4%, at both epochs, implying an asymmetry of the photosphere of <10%.
Similar to other Type Ibc SNe, such as 2005bf, 2006aj and 2007gr, we observed
significant polarization corresponding to the spectral features of Ca II, He I,
Mg I, Fe II and, possibly, O I 7774, about a close-to-spherically-symmetric
photosphere. We introduce a new plot showing the chemically distinct line
forming regions in the ejecta and comment on the apparent ubiquity of highly
polarized high-velocity Ca II features in Type Ibc SNe. The polarization angle
of Ca II IR triplet was significantly different, at both epochs, to those of
the other species, suggesting high-velocity Ca II forms in a separate part of
the ejecta. The apparent structure in the outer layers of SN 2008D has
implications for the interpretation of the early-time X-ray emission associated
with shock break-out. (abridged)Comment: ApJ Subm., 45 pages, 13 figure
Lightcurves of Type Ia Supernovae from Near the Time of Explosion
We present a set of 11 type Ia supernova (SN Ia) lightcurves with dense,
pre-maximum sampling. These supernovae (SNe), in galaxies behind the Large
Magellanic Cloud (LMC), were discovered by the SuperMACHO survey. The SNe span
a redshift range of z = 0.11 - 0.35. Our lightcurves contain some of the
earliest pre-maximum observations of SNe Ia to date. We also give a functional
model that describes the SN Ia lightcurve shape (in our VR-band). Our function
uses the "expanding fireball" model of Goldhaber et al. (1998) to describe the
rising lightcurve immediately after explosion but constrains it to smoothly
join the remainder of the lightcurve. We fit this model to a composite observed
VR-band lightcurve of three SNe between redshifts of 0.135 to 0.165. These SNe
have not been K-corrected or adjusted to account for reddening. In this
redshift range, the observed VR-band most closely matches the rest frame
V-band. Using the best fit to our functional description of the lightcurve, we
find the time between explosion and observed VR-band maximum to be
17.6+-1.3(stat)+-0.07(sys) rest-frame days for a SN Ia with a VR-band Delta
m_{-10} of 0.52mag. For the redshifts sampled, the observed VR-band
time-of-maximum brightness should be the same as the rest-frame V-band maximum
to within 1.1 rest-frame days.Comment: 35 pages, 18 figures, 15 tables; Higher quality PDF available at
http://ctiokw.ctio.noao.edu/~sm/sm/SNrise/index.html; AJ accepte
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