Found 6 talks width keyword X-ray
We present a detailed study of the spatially resolved thermodynamic and hydrostatic mass profiles of the five most massive clusters detected at z~1 via the Sunyaev-Zel'dovich effect. These objects represent an ideal laboratory to test our models in a mass regime where structure formation is driven mainly by gravity. We present a method to study these objects that optimally exploits information from XMM-Newton and Chandra observations. The combination of Chandra’s excellent spatial resolution and XMM-Newton’s photon collecting power allows us to spatially resolve the profiles from the core to the outskirts, for the first time in such objects. Evolution properties are investigated by comparison with the REXCESS local galaxy cluster sample. Finally, we discuss the current limitations of this method in the context of joint analysis of future Chandra and XMM large programs and, more generally, of multi-wavelength efforts to study high redshift objects.
Models of galaxy formation predict that gas accretion from the cosmic web is a primary driver of star formation over cosmic history. Except in very dense environments where galaxy mergers are also important, model galaxies feed from cold streams of gas from the web that penetrate their dark matter haloes. Although these predictions are unambiguous, the observational support has been indirect so far. I will report spectroscopic evidence for this process in extremely metal-poor galaxies (XMPs) of the local Universe, taking the form of localized starbursts associated with gas having low metallicity. Because gas mixes azimuthally in a rotation timescale (a few hundred Myr), the observed metallicity inhomogeneities are only possible if the metal-poor gas producing stars fell onto the disk recently. I will analyze several possibilities for the origin of the metal-poor gas, favoring the metal-poor gas infall predicted by numerical models. In addition, I will show model galaxies in cosmological numerical simulations with starbursts of low metallicity like to the star-forming regions in XMPs.
In the last years star-forming regions and massive protostars have been suggested to be gamma-ray emitters. Isolated massive protostars present powerful outflows interacting with the surrounding medium. Some of these sources power non-thermal radio jets, indicative of particle acceleration up to relativistic energies. At the jet-termination region strong shocks form which can lead to gamma-ray emission, as theoretical models predict. It has also been prognosticated that the combined effect of several low-mass protostellar objects may produce significant amount of gamma rays. We present here two studies: IRAS 16547- 4247, an isolated protostar showing non-thermal radio emission; and Monoceros R2, a star forming region coincident with a source of the 2nd Fermi-LAT catalog. In the first case, we analized archival X-ray data and detected the source. We also studied the system in a broad- band one-zone model context and tried to fit the X-ray detection with a non-thermal model. In the second case, we analyzed 3.5 years of Fermi-LAT data and confirmed the source with a detection above 12 sigma. Our results are compatible with the source being the result the combined effect of multiple young stellar objects in Monoceros R2.
Gamma-Ray Bursts (GRBs) are the most powerful sources of electromagnetic radiation in the Universe. There are many open questions about their origin and their nature, and the answers should be searched in the large amount of data collected during these last years. We focused on the study of the their X-ray and optical afterglow properties, as observed by the Swift X-Ray Telescope (XRT) and ground-based optical telescopes. We investigated the observer and rest-frame properties of all GRBs observed by Swift between December 2004 and December 2010 with spectroscopic redshift through a comprehensive statistical analysis of the XRT light-curves of GRBs carried out in a model-independent way. We found out a three parameter correlation that is followed both by short and long GRBs. We also carried out a systematic analysis of the optical data available in literature for the same GRBs to investigate the GRB emission mechanisms and to study their environment properties. Our analysis shows that the gas-to-dust ratios of GRBs are larger than the values calculated for the Milky Way, the Large Magellanic Cloud, and the Small Magellanic Cloud. In this talk I will show the major results of the analysis of this large set of data.
Neutron stars in low-mass X-ray binaries (NS-LMXBs) are unique laboratories of accretion physics, strong gravity and ultra-dense matter. I will give an overview of what we have learned in recent years by studying accretion flows and thermonuclear bursts in these systems.
I will first present and discuss the main result of a systematic study of their different accretion states: the discovery of a correlation between luminosity and spectral hardness. I will also show ongoing work on the connection between active (1-100% of the Eddington luminosity) and quiescent (down to 10^-6 times Eddington) phases of NS-LMXBs.
In the second part I will focus on the relation between mass accretion rate and the recurrence time of thermonuclear bursts (explosive nuclear burning on the neutron star surface), presenting results at the lowest and highest mass accretion rates. In particular, I will argue that rotation plays a larger role than we thought in setting the nuclear burning regimes on an accreting neutron star.
Extended, diffuse radio emission (halos and relics) in galaxy clusters is a rare phenomenon. The origin of these radio sources and their connection with cluster mergers is still being debated. Here we present the results of the DARC program, aimed to the internal Dynamics Analysis of ”Radio” Clusters and mainly based on a long-term TNG-INT program (20 clusters at z=0.1-0.3). The study of kinematics of member galaxies show that DARC clusters are examples of very substructured systems and allow us to detect and weight the interveining subclusters, as well as to obtain infor- mation about their relative motions and the merger geometry. The multiwavelength observational picture (optical, radio and X-ray) of DARC clusters is well interpreted in a scenario of a recent, major cluster merger.
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- Problems with the dark matter and dark energy hypotheses, and alternative ideasDr. Martin Lopez CorredoiraThursday October 25, 2018 - 10:30 (Aula)
- To Ba or not to Ba: Barium stars as tracers of binary interactionAna Escorza SantosMonday October 29, 2018 - 10:30 (Aula)