70 research outputs found
Photometric selection of high-redshift type Ia supernovae
We present a method for selecting high-redshift type Ia supernovae (SNe Ia)
located via rolling SN searches. The technique, using both color and magnitude
information of events from only 2-3 epochs of multi-band real-time photometry,
is able to discriminate between SNe Ia and core collapse SNe. Furthermore, for
the SNe Ia, the method accurately predicts the redshift, phase and light-curve
parameterization of these events based only on pre-maximum-light data. We
demonstrate the effectiveness of the technique on a simulated survey of SNe Ia
and core-collapse SNe, where the selection method effectively rejects most
core-collapse SNe while retaining SNe Ia. We also apply the selection code to
real-time data acquired as part of the Canada-France-Hawaii Telescope Supernova
Legacy Survey (SNLS). During the period May 2004 to January 2005 in the SNLS,
440 SN candidates were discovered of which 70 were confirmed spectroscopically
as SNe Ia and 15 as core-collapse events. For this test dataset, the selection
technique correctly identifies 100% of the identified SNe II as non-SNe Ia with
only a 1-2% false rejection rate. The predicted parameterization of the SNe Ia
has a precision of |delta_z|/(1+z_spec)<0.09 in redshift, and +/- 2-3
rest-frame days in phase, providing invaluable information for planning
spectroscopic follow-up observations. We also investigate any bias introduced
by this selection method on the ability of surveys such as SNLS to measure
cosmological parameters (e.g., w and omega matter), and find any effect to be
negligible.Comment: Accepted for publication in A
The Rise Time of Type Ia Supernovae from the Supernova Legacy Survey
We compare the rise times of nearby and distant Type Ia supernovae (SNe Ia)
as a test for evolution using 73 high-redshift spectroscopically-confirmed SNe
Ia from the first two years of the five year Supernova Legacy Survey (SNLS) and
published observations of nearby SN. Because of the ``rolling'' search nature
of the SNLS, our measurement is approximately 6 times more precise than
previous studies, allowing for a more sensitive test of evolution between
nearby and distant supernovae. Adopting a simple early-time model (as in
previous studies), we find that the rest-frame rise times for a fiducial SN
Ia at high and low redshift are consistent, with values
and
days, respectively; the statistical significance of this difference is only 1.4
\sg . The errors represent the uncertainty in the mean rather than any
variation between individual SN. We also compare subsets of our high-redshift
data set based on decline rate, host galaxy star formation rate, and redshift,
finding no substantive evidence for any subsample dependence.Comment: Accepted for publication in AJ; minor changes (spelling and
grammatical) to conform with published versio
A Categorical Treatment of Malicious Behavioral Obfuscation
International audienceThis paper studies malicious behavioral obfuscation through the use of a new abstract model for process and kernel interactions based on monoidal categories. In this model, program observations are consid-ered to be finite lists of system call invocations. In a first step, we show how malicious behaviors can be obfuscated by simulating the observa-tions of benign programs. In a second step, we show how to generate such malicious behaviors through a technique called path replaying and we extend the class of captured malwares by using some algorithmic transformations on morphisms graphical representation. In a last step, we show that all the obfuscated versions we obtained can be used to detect well-known malwares in practice
Cube Testers and Key Recovery Attacks On Reduced-Round MD6 and Trivium
CRYPTO 2008 saw the introduction of the hash function
MD6 and of cube attacks, a type of algebraic attack applicable to cryptographic
functions having a low-degree algebraic normal form over GF(2).
This paper applies cube attacks to reduced round MD6, finding the full
128-bit key of a 14-round MD6 with complexity 2^22 (which takes less
than a minute on a single PC). This is the best key recovery attack announced
so far for MD6. We then introduce a new class of attacks called
cube testers, based on efficient property-testing algorithms, and apply
them to MD6 and to the stream cipher Trivium. Unlike the standard
cube attacks, cube testers detect nonrandom behavior rather than performing
key extraction, but they can also attack cryptographic schemes
described by nonrandom polynomials of relatively high degree. Applied
to MD6, cube testers detect nonrandomness over 18 rounds in 2^17 complexity;
applied to a slightly modified version of the MD6 compression
function, they can distinguish 66 rounds from random in 2^24 complexity.
Cube testers give distinguishers on Trivium reduced to 790 rounds from
random with 2^30 complexity and detect nonrandomness over 885 rounds
in 2^27, improving on the original 767-round cube attack
SALT2: using distant supernovae to improve the use of Type Ia supernovae as distance indicators
We present an empirical model of Type Ia supernovae spectro-photometric
evolution with time. The model is built using a large data set including
light-curves and spectra of both nearby and distant supernovae, the latter
being observed by the SNLS collaboration. We derive the average spectral
sequence of Type Ia supernovae and their main variability components including
a color variation law. The model allows us to measure distance moduli in the
spectral range 2500-8000 A with calculable uncertainties, including those
arising from variability of spectral features. Thanks to the use of
high-redshift SNe to model the rest-frame UV spectral energy distribution, we
are able to derive improved distance estimates for SNe Ia in the redshift range
0.8<z<1.1. The model can also be used to improve spectroscopic identification
algorithms, and derive photometric redshifts of distant Type Ia supernovae.Comment: Accepted for publication in A&A. Data and source code available at :
http://supernovae.in2p3.fr/~guy/salt
Advanced Detection Tool for PDF Threats
In this paper we introduce an efficient application for malicious PDF detection: ADEPT. With targeted attacks rising over the recent past, exploring a new detection and mitigation paradigm becomes mandatory. The use of malicious PDF files that exploit vulnerabilities in well-known PDF readers has become a popular vector for targeted at- tacks, for which few efficient approaches exist. Although simple in theory, parsing followed by analysis of such files is resource-intensive and may even be impossible due to several obfuscation and reader-specific artifacts. Our paper describes a new approach for detecting such malicious payloads that leverages machine learning techniques and an efficient feature selection mechanism for rapidly detecting anomalies. We assess our approach on a large selection of malicious files and report the experimental performance results for the developed prototype
The Supernova Type Ia Rate Evolution with SNLS
We present a progress report on a project to derive the evolution of the volumetric supernova Type Ia rate from the Supernova Legacy Survey. Our preliminary estimate of the rate evolution divides the sample from Neill et al. into two redshift bins: 0.2 < z < 0.4, and 0.4 < z < 0.6. We extend this by adding a bin from the sample analyzed in Sullivan et al. in the range 0.6 < z < 0.75 from the same time period. We compare the derived trend with previously published rates and a supernova Type Ia production model having two components: one component associated closely with star formation and an additional component associated with host galaxy mass. Our observed trend is consistent with this model, which predicts a rising SN Ia rate out to at least z = 2
Rates and properties of type Ia supernovae as a function of mass and star-formation in their host galaxies
(ABRIDGED) We show that Type Ia supernovae (SNe Ia) are formed within both
very young and old stellar populations, with observed rates that depend on the
stellar mass and mean star-formation rates (SFRs) of their host galaxies.
Models where the SN Ia rate depends solely on host galaxy stellar mass are
ruled out with 99% confidence. Our analysis is based on 100
spectroscopically-confirmed SNe Ia, plus 24 photometrically-classified events,
all from the Supernova Legacy Survey (SNLS) and distributed over 0.2<z<0.75.
Using multi-band photometry, we estimate stellar masses and SFRs for the SN Ia
host galaxies by fitting their broad-band spectral energy distributions with
the galaxy spectral synthesis code, PEGASE.2. We show that the SN Ia rate per
unit mass is proportional to the specific SFR of the parent galaxies -- more
vigorously star-forming galaxies host more SNe Ia per unit stellar mass,
broadly equivalent to the trend of increasing SN Ia rate in later-type galaxies
seen in the local universe. Following earlier suggestions for a simple
"two-component" model approximating the SN Ia rate, we find bivariate linear
dependencies of the SN Ia rate on both the stellar masses and the mean SFRs of
the host systems. We also demonstrate a dependence of distant SN Ia light-curve
shapes on star-formation in the host galaxy, similar to trends observed
locally. Passive galaxies, with no star-formation, preferentially host
faster-declining/dimmer SNe Ia, while slower-declining/brighter events are only
found in systems with ongoing star-formation. We model the light-curve width
distribution in star-forming galaxies as the sum of a young component, and an
old component taken from the distribution in non-star-forming galaxies.Comment: Accepted for publication in Ap
The Type Ia Supernova Rate at z ~0.5 from the Supernova Legacy Survey
We present a measurement of the distant Type Ia supernova rate derived from
the first two years of the Canada -- France -- Hawaii Telescope Supernova
Legacy Survey. We observed four one-square degree fields with a typical
temporal frequency of ~ 4 observer-frame days over time spans of from
158 to 211 days per season for each field, with breaks during full moon. We
used 8-10 meter-class telescopes for spectroscopic followup to confirm our
candidates and determine their redshifts. Our starting sample consists of 73
spectroscopically verified Type Ia supernovae in the redshift range 0.2 < z <
0.6. We derive a volumetric SN Ia rate of r_V(=0.47) = 0.42^{+0.13}_{-0.09}
(systematic) +- 0.06 (statistical) X 10^-4 yr^-1 Mpc^3, assuming h = 0.7,
Omega_m = 0.3 and a flat cosmology. Using recently published galaxy luminosity
functions derived in our redshift range, we derive a SN Ia rate per unit
luminosity of r_L(=0.47) = 0.154^{+0.048}_{-0.033} (systematic)
^{+0.039}_{-0.031} (statistical) SNu. Using our rate alone, we place an upper
limit on the component of SN Ia production that tracks the cosmic star
formation history of 1 SN Ia per 10^3 M_sun of stars formed. Our rate and other
rates from surveys using spectroscopic sample confirmation display only a
modest evolution out to z=0.55.Comment: 71 pages, 12 figures, accepted for publication in AJ, fixed typos in
Eq 3 and
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