727 research outputs found
The Distribution of High and Low Redshift Type Ia Supernovae
The distribution of high redshift Type Ia supernovae (SNe Ia) with respect to
projected distance from the center of the host galaxy is studied and compared
to the distribution of local SNe. The distribution of high-z SNe Ia is found to
be similar to the local sample of SNe Ia discovered with CCDs, but different
than the sample discovered photographically. This is shown to be due to the
Shaw effect. These results have implications for the use of SNe Ia to determine
cosmological parameters if the local sample of supernovae used to calibrate the
light curve decline relationships is drawn from a sample discovered
photographically. A K-S test shows that the probability that the high redshift
SNe of the Supernova Cosmology Project are drawn from the same distribution as
the low redshift calibrators of Riess et al. is 0.1%. This is a potential
problem because photographically discovered SNe are preferentially discovered
farther away from the galaxy nucleus, where SNe show a lower scatter in
absolute magnitude, and are on average 0.3 magnitudes fainter than SNe located
closer to the center of their host galaxy. This raises questions about whether
or not the calibration SNe sample the full range of parameters potentially
present in high redshift SNe Ia. The limited data available suggest that the
calibration process is adequate; however, it would be preferable if high
redshift SNe and the low redshift SNe used to calibrate them were drawn from
the same sample, as subtle differences may be important. Data are also
presented which suggest that the seeming anti-Malmquist trend noticed by
Tammann et al.(1996, 1998) for SNe Ia in galaxies with Cepheid distances may be
due to the location of the SNe in their host galaxies.Comment: 16 pages, 2 figures Accepted for publication in the Astrophysical
Journa
The Asiago Supernova Catalogue- 10 years after
Ten years after the publication of the previous release, we present a new
edition of the Asiago Supernova Catalogue updated to December 31, 1998 and
containing data for 1447 supernovae and their parent galaxies\footnote{Tables 1
and 2 are only available in electronic form at the CDS via anonymous ftp to
cdsarc.u-strasbg.fr (130.79.128.5) or via
http://cdsweb.u-strasbg.fr/Abstract.html}. In addition to list the data for a
large number of new SNe, we made an effort to search the literature for new
information on past SNe as well. We also tried to update and homogenize the
data for the parent galaxies. To allow a global view of the Catalogue, a few
descriptive figures and a summary table is reported. The present Catalogue is
intended as a large and modern database for statistical studies on the
supernova phenomenon.Comment: 6 pages. To be published in A&A supplement. Enclosed as postscript
files are the full lists in chronological (snean.ps) and R.A. (snear.ps)
order (to be published only in electronic form.
Fast Scramblers Of Small Size
We investigate various geometrical aspects of the notion of `optical depth'
in the thermal atmosphere of black hole horizons. Optical depth has been
proposed as a measure of fast-crambling times in such black hole systems, and
the associated optical metric suggests that classical chaos plays a leading
role in the actual scrambling mechanism. We study the behavior of the optical
depth with the size of the system and find that AdS/CFT phase transitions with
topology change occur naturally as the scrambler becomes smaller than its
thermal length. In the context of detailed AdS/CFT models based on D-branes,
T-duality implies that small scramblers are described in terms of matrix
quantum mechanics.Comment: 14 pages, 3 figures. Added reference
The Risetime of Nearby Type Ia Supernovae
We present calibrated photometric measurements of the earliest detections of
nearby type Ia supernovae (SNe Ia). The set of ~30 new, unfiltered CCD
observations delineate the early rise behavior of SNe Ia > 18 to 10 days before
maximum. Using simple empirical models, we demonstrate the strong correlation
between the risetime (i.e., the time between explosion and maximum), the
post-rise light-curve shape, and the peak luminosity. Using a variety of
light-curve shape methods, we find the risetime to B maximum for a SN Ia with
Delta m15(B)=1.1 mag and peak M_V=-19.45 mag to be 19.5+/-0.2 days. We find
that the peak brightness of SNe Ia is correlated with their risetime; SNe Ia
which are 0.10 mag brighter at peak in the B-band require 0.80+/-0.05 days
longer to reach maximum light.
We determine the effects of several possible sources of systematic errors,
but none of these significantly impacts the inferred risetime. Constraints on
SN Ia progenitor systems and explosion models are derived from a comparison
between the observed and theoretical predictions of the risetime.Comment: Submitted to the Astronomical Journal, 24 pages, 7 figure
Remarks on Time-Space Noncommutative Field Theories
We propose a physical interpretation of the perturbative breakdown of
unitarity in time-like noncommutative field theories in terms of production of
tachyonic particles. These particles may be viewed as a remnant of a continuous
spectrum of undecoupled closed-string modes. In this way, we give a unified
view of the string-theoretical and the field-theoretical no-go arguments
against time-like noncommutative theories. We also perform a quantitative study
of various locality and causality properties of noncommutative field theories
at the quantum level.Comment: 19 pages, LaTe
The Late Time Light Curve of SN 1998bw Associated with GRB980425
We report 139 photometric observations through the B, V, and I filters of the
supernova SN 1998bw, an object which is associated with the Gamma-Ray Burst GRB
980425. Detailed light curves of this unique supernova can be compared to
theoretical models, so we report here our light curve for 123 days between 27
June 1998 and 28 October 1998. The light curve of SN 1988bw is consistent with
those of the Type Ic class. We find that the magnitude-versus-time relation for
this supernova is linear to within 0.05 mags in all colors over the entire
duration of our study. Our measured uniform decline rates are , , and magnitudes per day in the
B, V, and I bands. The linear decline and the rate of that decline suggest that
late time light curve is powered by the radioactive decay of cobalt with some
leakage of the gamma rays.Comment: 15 pages, 1 figure, 1 table, Accepted for publication in PAS
Spectroscopy and BVI photometry of the young open cluster NGC 6604
BVI photometry (from South Africa Astron. Obs.), Echelle high resolution
spectroscopy and AFOSC integral field spectroscopy (from Asiago, Italy) of the
young open cluster NGC 6604 are presented. Age, distance, reddening,
membership, radial and rotational velocities are derived and discussed. An age
of 5 million years, a distance of 1.7 kpc and a reddening E(B-V)=1.02 are
found. The cluster radial velocity is in agreement with the Hron (1987) model
for the Galaxy disk rotation. Pre-ZAMS objects are not present down to M_V =
+1.5 mag.Comment: accepted in Astron.Astrophys.Suppl. Figure 2 is degraded in
resolutio
Type II Supernovae as Standardized Candles
We present evidence for a correlation between expansion velocities of the
ejecta of Type II plateau supernovae and their bolometric luminosities during
the plateau phase. This correlation permits one to standardize the candles and
decrease the scatter in the Hubble diagram from ~1 mag to a level of 0.4 and
0.3 mag in the V and I bands, respectively. When we restrict the sample to the
eight objects which are well in the Hubble flow (cz > 3,000 km/s) the scatter
drops even further to only 0.2 mag (or 9% in distance), which is comparable to
the precision yielded by Type Ia supernovae and far better than the ``expanding
photosphere method'' applied to Type II supernovae. Using SN 1987A to calibrate
the Hubble diagrams we get Ho=55+/-12.Comment: 9 pages, 3 figures, 1 table, accepted by ApJ
Optical Photometry of Type II-P Supernova 2004dj in NGC 2403
We present photometric data of the type II-P supernova (SN) 2004dj in NGC
2403. The multicolor light curves cover the SN from 60 to 200 days after
explosion, and are measured with a set of intermediate-band filters that have
the advantage of tracing the strength variations of some spectral features. The
light curves show a flat evolution in the middle of the plateau phase, then
decline exponentially at the late times, with a rate of 0.100.03 mag (10
days) in most of the filters. In the nebular phase, the spectral energy
distribution (SED) of SN 2004dj shows a steady increase in the flux near 6600
\AA and 8500 \AA, which may correspond to the emission lines of H and
Ca II near-IR triplet, respectively. The photometric behavior suggests that SN
2004dj is a normal SN II-P. Compared with the light curves of another typical
SN II-P 1999em, we estimate the explosion date to be June 1021 UT, 2004
(JD 245316721) for SN 2004dj. We also estimate the ejected nickel mass
during the explosion to be = 0.023 0.005
from two different methods, which is typical for a SN II-P. We derive the
explosion energy erg, the ejecta
mass , and the initial radius for the presupernova star of SN 2004dj,
which are consistent with other typical SNe II-P.Comment: 15 pages, 9 figures, accepted for publication in A
Constraints on the Massive Supernova Progenitors
Generally accepted scheme distinguishes two main classes of supernovae (SNe):
Ia resulting from the old stellar population (deflagration of a white dwarf in
close binary systems), and SNe of type II and Ib/c whose ancestors are young
massive stars (died in a core-collapse explosion). Concerning the latter, there
are suggestions that the SNe II are connected to early B stars, and SNe Ib/c to
isolated O or Wolf-Rayet (W-R) stars. However, little or no effort was made to
further separate SNe Ib from Ic. We have used assumed SN rates for different SN
types in spiral galaxies in an attempt to perform this task. If isolated
progenitor hypothesis is correct, our analysis indicates that SNe Ib result
from stars of main-sequence mass , while the progenitors of SNe Ic are more
massive stars with .
Alternatively, if the majority of SNe Ib/c appear in close binary systems
(CBs) then they would result from the same progenitor population as most of the
SNe II, i.e. early B stars with initial masses of order . Future observations of SNe at high-redshift () and
their rate will provide us with unique information on SN progenitors and
star-formation history of galaxies. At higher- (deeper in the cosmic past)
we expect to see the lack of type Ia events, i.e. the dominance of
core-collapse SNe. Better understanding of the stripped-envelope SNe (Ib/c),
and their potential use as distance indicators at high-, would therefore be
of great practical importance.Comment: 11 pages, 2 figures, accepted for publication in IJMP
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