Search results for "astronomia"
showing 10 items of 673 documents
All-sky search for short gravitational-wave bursts in the second Advanced LIGO and Advanced Virgo run
2019
We present the results of a search for short-duration gravitational-wave transients in the data from the second observing run of Advanced LIGO and Advanced Virgo. We search for gravitational-wave transients with a duration of milliseconds to approximately one second in the 32-4096 Hz frequency band with minimal assumptions about the signal properties, thus targeting a wide variety of sources. We also perform a matched-filter search for gravitational-wave transients from cosmic string cusps for which the waveform is well-modeled. The unmodeled search detected gravitational waves from several binary black hole mergers which have been identified by previous analyses. No other significant event…
Accreting X-Ray pulsars. The high energy picture
2007
El objetivo principal de esta tesis ha sido el estudio del comportamiento transitorio durante estallidos de distinto tipo, de una selección de pulsares acretores en rayos X, localizados en el plano galáctico.Con ello se pretende haber avanzado hacia una explicación más clara de la naturaleza de estas objetos binarios de alta masa (con estrella de neutrones como objeto compacto), así como de los mecanismos físicos que operan en este escenario. Para todo esto se han analizado datos de dos misiones espaciales:INTEGRA Y RXTE.El segundo objetivo ha sido el estudio de la zona del brazo galactico de Scutum. Al ser esta una región de fuerte absorción se cree de la existencia de sistemas del tipo an…
Limits on the high-energy gamma and neutrino fluxes from the SGR 1806-20 giant flare of 27 December 2004 with the AMANDA-II detector.
2006
On December 27th 2004, a giant gamma flare from the Soft Gamma-ray Repeater 1806-20 saturated many satellite gamma-ray detectors. This event was by more than two orders of magnitude the brightest cosmic transient ever observed. If the gamma emission extends up to TeV energies with a hard power law energy spectrum, photo-produced muons could be observed in surface and underground arrays. Moreover, high-energy neutrinos could have been produced during the SGR giant flare if there were substantial baryonic outflow from the magnetar. These high-energy neutrinos would have also produced muons in an underground array. AMANDA-II was used to search for downgoing muons indicative of high-energy gamm…
Five years of searches for point sources of astrophysical neutrinos with the AMANDA-II neutrino telescope
2007
We report the results of a five-year survey of the northern sky to search for point sources of high energy neutrinos. The search was performed on the data collected with the AMANDA-II neutrino telescope in the years 2000 to 2004, with a live-time of 1001 days. The sample of selected events consists of 4282 upward going muon tracks with high reconstruction quality and an energy larger than about 100 GeV. We found no indication of point sources of neutrinos and set 90% confidence level flux upper limits for an all-sky search and also for a catalog of 32 selected sources. For the all-sky search, our average (over declination and right ascension) experimentally observed upper limit \Phi^{0}=(E/…
Multiyear search for a diffuse flux of muon neutrinos with AMANDA-II
2007
A search for TeV - PeV muon neutrinos from unresolved sources was performed on AMANDA-II data collected between 2000 and 2003 with an equivalent livetime of 807 days. This diffuse analysis sought to find an extraterrestrial neutrino flux from sources with non-thermal components. The signal is expected to have a harder spectrum than the atmospheric muon and neutrino backgrounds. Since no excess of events was seen in the data over the expected background, an upper limit of E^{2}\Phi_{90% C.L.} < 7.4 x 10^{-8} GeV cm^{-2} s^{-1} sr^{-1} is placed on the diffuse flux of muon neutrinos with a \Phi \propto E^{-2} spectrum in the energy range 16 TeV to 2.5 PeV. This is currently the most sensitive…
First year performance of the IceCube neutrino telescope
2006
The first sensors of the IceCube neutrino observatory were deployed at the South Pole during the austral summer of 2004-2005 and have been producing data since February 2005. One string of 60 sensors buried in the ice and a surface array of eight ice Cherenkov tanks took data until December 2005 when deployment of the next set of strings and tanks began. We have analyzed these data, demonstrating that the performance of the system meets or exceeds design requirements. Times are determined across the whole array to a relative precision of better than 3 ns, allowing reconstruction of muon tracks and light bursts in the ice, of air-showers in the surface array and of events seen in coincidence…
Recent Advances in Bayesian Inference in Cosmology and Astroparticle Physics Thanks to the MultiNest Algorithm
2012
We present a new algorithm, called MultiNest, which is a highly efficient alternative to traditional Markov Chain Monte Carlo (MCMC) sampling of posterior distributions. MultiNest is more efficient than MCMC, can deal with highly multi-modal likelihoods and returns the Bayesian evidence (or model likelihood, the prime quantity for Bayesian model comparison) together with posterior samples. It can thus be used as an all-around Bayesian inference engine. When appropriately tuned, it also provides an exploration of the profile likelihood that is competitive with what can be obtained with dedicated algorithms.
X-raying hadronic acceleration at the SN 1006 shock front
2012
Shock fronts in young supernova remnants are the best candidates for being sites of cosmic rays acceleration up to a few PeV, though conclusive experimental evidence is still lacking. Theoretical models predict that particle acceleration can modify the post-shock properties, e. g. by increasing the plasma density. We exploited the Large Program of deep XMM-Newton observations of SN 1006 to verify this prediction. We focused on the rim of the supernova remnant and by performing spatially resolved spectral analysis, we found that the shock compression ratio significantly increases in regions where particle acceleration is efficient, in agreement with expectations. Our results provide observat…
Coupled dark matter-dark energy in light of near Universe observations
2010
Cosmological analysis based on currently available observations are unable to rule out a sizeable coupling among the dark energy and dark matter fluids. We explore a variety of coupled dark matter-dark energy models, which satisfy cosmic microwave background constraints, in light of low redshift and near universe observations. We illustrate the phenomenology of different classes of dark coupling models, paying particular attention in distinguishing between effects that appear only on the expansion history and those that appear in the growth of structure. We find that while a broad class of dark coupling models are effectively models where general relativity (GR) is modified - and thus can b…
The B0.5IVe CoRoT target HD 49 330. I. Photometric analysis from CoRoT data
2009
Context. Be stars undergo outbursts producing a circumstellar disk from the ejected material. The beating of non-radial pulsations has been put forward as a possible mechanism of ejection. Aims. We analyze the pulsational behavior of the early B0.5IVe star HD 49330 observed during the first CoRoT long run towards the Galactical anticenter (LRA1). This Be star is located close to the lower edge of the β Cephei instability strip in the HR diagram and showed a 0.03 mag outburst during the CoRoT observations. It is thus an ideal case for testing the aforementioned hypothesis. Methods. We analyze the CoRoT light curve of HD 49330 usin g Fourier methods and non-lin ear least square fitting. Resul…