PTDC/CTE-AST/64972/2006: SNa and GRB´s

Resumo
As supernovas do tipo Ia e as explosões de raios gama são os fenómenos mais energéticos no Universo e, por esse motivo, são detectados a distâncias cosmológicas de milhares de milhões de anos luz. O estudo destes fenómenos pode assim ser usado para compreender a evolução e destino do Universo.
De facto, foi o trabalho pioneiro desenvolvido por duas colaborações internacionais, o Supernova Cosmology Project e High-z Supernova team, que levou à descoberta da expansão acelerada do Universo em 1998. Esta expansão é devida à existência de uma forma de energia desconhecida que ocupa cerca de 70% do Universo, contraria a gravidade e a que se chama energia escura. Porém, estes resultados poderão ter erros sistemá- ticos relacionados com as propriedades quer das supernovas quer das próprias galáxias onde ocorreram.
O uso de explosões de raios gama em Cosmologia é um desafio mais recente e exige uma melhor compreensão destes fenómenos astrofísicos.
O objectivo deste projecto consiste no estudo de propriedades de supernovas (SN) e das explosões de raios gama (ERG) que podem influenciar a nossa compreensão do modelo cosmológico do Universo. Pretende-se ainda perceber até que ponto as propriedades das galáxias influenciam as propriedades de SN ou ERG, para tentar encontrar possíveis erros sistemáticos.
Estudantes de doutoramento e jovens investigadores serão especialmente incentivados a participar no trabalho da equipa.



Abstract
Type Ia Supernova and gamma ray bursts are now considered the most energetic events in the Universe and for this reason detectable at cosmological distances. The main goal of this project is to understand the use of SN Ia and GRB as secure tools to measure cosmological parameters with high precision, and check for systematic errors associated with their host galactic properties.
Type Ia supernovae (SN Ia) have been intensively used in the last decades as the best standard candles to measure cosmological distances up to redshifts <~1.5. Such an effort led to the astonishing discovery in 1998 that the Universe is expanding with acceleration due to an unexplained energy component, called dark energy, that has been commonly associated with a cosmological constant. This result was achieved independently by the Supernova Cosmology Project and the High z Supernova Search Team. Measuring the cosmological parameters and the equation of state of the Universe with high precision, with control of systematic effects is currently one of major tasks in modern cosmology.
Recently, using multiband photometry of 71 high redshift SN Ia obtained with the CFHT, the Supernova Legacy Survey announced that the results from the first year give Omega_M=0.263 for a flat Lambda CDM and w=-1.023+-0.09 (stat)+-0.054 (sys). CENTRA participates in this collaboration and had a relevant contribution to the supernova (SN) discovery and the implementation of data analysis pipelines.
However the new data sets revealed SNe Ia peculiarities, and further searches for systematic errors hidden by host galaxies properties, that might affect our understanding of SN Ia, are highly desired. New telescope facilities and new data analysis techniques for the determination of extinction in host galaxies, studies of correlations between SN and host galaxy properties in search for metallicity and evolution effects are critical.
More recently, Gamma Ray Bursts (GRBs) have been also tested as new tools in Cosmology. Discovered only in 1969, are probably the most powerful explosions in the universe, and are unique cosmic events. Due to the extreme luminosity of optical emissions, GRBs are now considered as one of the best ways to probe the most distant universe.
By studying the nature of the GRB progenitors and by trying to use them in cosmology, it is possible to put in common the knowledge acquired in these different fields to obtain a significant contribution to the understanding of the GRBs progenitors. One motivation of this proposal is to study the GRB formation mechanisms by studying in details their environment and the properties of their host galaxy, while preparing the next generation observational programs. We propose to characterize the host galaxy properties by acquiring a high-resolution spectrum when the GRBs have already disappeared (i.e. several months after the detection). The same technique will be used to study galaxies, hosts of SNe.

One of the institutes of our team (Observatoire de Paris) is coordinating the ESO Large Program IMAGES- Intermediate MAss Galaxies Evolution Sequences and is involved in X-Shooter, a single target spectrograph for the ESO/VLT. Our team will have a privileged access to the Scientific commissioning and to the Guarantee time (20 nights).
Due to the future access to the X-Shooter, the team members aim at converging their scientific activities to explore the remarkable potentialities given by this instrument. It is a natural evolution for the members which have already worked on similar research domains: galaxy evolution, supernova evolution and cosmological consequences, production of synthetic galaxy spectra and use of new mathematical tools applied to astronomical data analysis.
The current data from IMAGES and the observations from X-Shooter will reveal the properties of the host galaxies: metal abundances, electronic density, extinction, determine the host galaxy stellar population.

These objectives will allow us to contribute very significantly to understand several fundamental questions: Are there any significant systematic errors in the determination of SN host galaxy extinction from spectra, comparing with the commonly used photometric determination of extinction? What is the correlation between host galaxy properties and intrinsic SN luminosity? Are the GRBs an acceptable candle to measure the cosmological parameters? Can we use the GRBs to trace the star formation rate in the early Universe?
Our scientific objectives are of course intrinsically linked and will be pursued in parallel.
The aim of this project is also to support the research of young students by supporting their research and creating an international productive atmosphere.

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Registo de descoberta de Supernovas

SUPERNOVAE 2000bt, 2000bu, 2000bv, 2000bw, 2000bx, 2000by, 2000bz
R. Knop et al (Supernova Cosmology Project) (com A. Mourão)
INTERNATIONAL ASTRONOMICAL UNION Circular No. 7128

SUPERNOVAE 2000bt, 2000bu, 2000bv, 2000bw, 2000bx, 2000by, 2000bz
D. Hardin, LPNHE, Paris, reports for N. Walton, on behalf of
the EROS collaboration and the European Supernova Cosmology
Consortium (cf. IAUC 7258, plus A. Amadon, Service de Physique des
Particules, Saclay; D. Batcheldor, University of Hertfordshire; G.
Folatelli, G. Garavini, and S. Nobili, University of Stockholm; and
A. Mourao and M. J. Cruz, Instituto Superior Tecnico, Lisbon)
INTERNATIONAL ASTRONOMICAL UNION Circular No. 7406

SUPERNOVAE 2002li-2002ls
P. Ruiz-Lapuente, University of Barcelona, on behalf of the
European Supernova Cosmology Consortium (cf. IAUC 7406, plus A.
Balastegui, G. Sainton, R. Pascoal, and R. Amanullah),
INTERNATIONAL ASTRONOMICAL UNION Circular No. 8181