Search results for "astronomia"
showing 10 items of 673 documents
Laboratory unraveling of matter accretion in young stars
2017
When matter accretes onto a young star, a shell of dense material can form around the impact, reducing its x-ray emission.
El cometa de Halley y la imagen pública de la astronomía en la prensa diaria española de principios del siglo XX
2013
Este texto pretende mostrar algunos aspectos de las representaciones formadas en la opinión pública española acerca de la astronomía y la astrofísica, a partir del análisis de las noticias publicadas en algunas de las cabeceras más destacadas con motivo de la aparición del cometa de Halley en 1910. El interés despertado por la llegada de este cometa estuvo íntimamente ligado a su asociación con diferentes desastres y calamidades, representado en este caso por el equipaje de gases mortíferos que portaba y que desató una inquietud generalizada entre una parte importante de la población. Esta preocupación sirvió para reforzar y legitimar frente a la opinión pública la actividad desarrollada po…
Fabrication of Bismuth Absorber Arrays for NTD-Ge Hard X-ray Microcalorimeters
2020
The high-spectral-resolution detection of hard X-rays (E > 20 keV) is a challenging and nearly unexplored area in space astrophysics. Traditionally hard X-ray detectors present moderate spectral resolutions, although few tens of eV one could open new frontiers in the study of nuclear processes and high-temperature plasma dynamics in energetic processes. This can be achieved by using cryogenic microcalorimeters. Within a research activity aimed at developing arrays of neutron transmutation-doped germanium (NTD-Ge) microcalorimeters for the high-spectral-resolution detection (about 50 eV@60 keV) of hard X-rays (20 keV < E<100 keV), we developed an electroplating process to fabricate …
On the peculiar long-term orbital evolution of the eclipsing accreting millisecond X-ray pulsar SWIFT J1749.4-2807
2022
We present the pulsar timing analysis of the accreting millisecond X-ray pulsar SWIFT J1749.4-2807 monitored by NICER and XMM-Newton during its latest outburst after almost eleven years of quiescence. From the coherent timing analysis of the pulse profiles, we updated the orbital ephemerides of the system. Large phase jumps of the fundamental frequency phase of the signal are visible during the outburst, consistent with what was observed during the previous outburst. Moreover, we report on the marginally significant evidence for non-zero eccentricity ($e\simeq 4\times 10^{-5}$) obtained independently from the analysis of both the 2021 and 2010 outbursts and we discuss possible compatible sc…
MOJAVE. X. Parsec-Scale Jet Orientation Variations and Superluminal Motion in AGN
2013
We describe the parsec-scale kinematics of 200 AGN jets based on 15 GHz VLBA data obtained between 1994 Aug 31 and 2011 May 1. We present new VLBA 15 GHz images of these and 59 additional AGN from the MOJAVE and 2 cm Survey programs. Nearly all of the 60 most heavily observed jets show significant changes in their innermost position angle over a 12 to 16 year interval, ranging from 10 deg to 150 deg on the sky, corresponding to intrinsic variations of ~0.5 deg to ~2 deg. The BL Lac jets show smaller variations than quasars. Roughly half of the heavily observed jets show systematic position angle trends with time, and 20 show indications of oscillatory behavior. The time spans of the data se…
Constant circulation sequences of binary neutron stars and their spin characterization
2018
For isentropic fluids, dynamical evolution of a binary system conserves the baryonic mass and circulation; therefore, sequences of constant rest mass and constant circulation are of particular importance. In this work, we present the extension of our Compact Object CALculator (\cocal{}) code to compute such quasiequilibria and compare them with the well-known corotating and irrotational sequences, the latter being the simplest, zero-circulation case. The circulation as a measure of the spin for a neutron star in a binary system has the advantage of being exactly calculable since it is a local quantity. To assess the different measures of spin, such as the angular velocity of the star, the q…
The supernova remnant SN 1006 as a Galactic particle accelerator
2022
The origin of cosmic rays is a pivotal open issue of high-energy astrophysics. Supernova remnants are strong candidates to be the Galactic factory of cosmic rays, their blast waves being powerful particle accelerators. However, supernova remnants can power the observed flux of cosmic rays only if they transfer a significant fraction of their kinetic energy to the accelerated particles, but conclusive evidence for such efficient acceleration is still lacking. In this scenario, the shock energy channeled to cosmic rays should induce a higher post-shock density than that predicted by standard shock conditions. Here we show this effect, and probe its dependence on the orientation of the ambient…
Outflows and spectral evolution in the eclipsing AMXP SWIFT J1749.4–2807 with NICER, XMM-Newton, and NuSTAR
2022
The neutron star low-mass X-ray binary SWIFT J1749.4–2807 is the only known eclipsing accreting millisecond X-ray pulsar. In this manuscript, we perform a spectral characterization of the system throughout its 2021, 2-week-long outburst, analysing 11 NICER observations and quasi-simultaneous XMM-Newton and NuSTAR single observations at the outburst peak. The broad-band spectrum is well-modelled with a blackbody component with a temperature of ∼0.6 keV, most likely consistent with a hotspot on the neutron star surface, and a Comptonization spectrum with power-law index Γ ∼ 1.9, arising from a hot corona at ∼12 keV. No direct emission from the disc was found, possibly due to it being too cool…
Millimeter-VLBI observations of low-luminosity active galactic nuclei with source-frequency phase-referencing
2021
We report millimeter-VLBI results of low-luminosity active galactic nuclei (M 84 and M 87) up to 88 GHz with source-frequency phase-referencing observations. We detected the weak VLBI core and obtained the first image of M 84 at 88 GHz. The derived brightness temperature of M 84 core was about 7.2$\times$10$^9$ K, which could serve as a lower limit as the core down to 30 Schwarzschild radii was still un-resolved in our 88 GHz observations. We successfully determined the core-shifts of M 87 at 22-44 GHz and 44-88 GHz through source-frequency phase-referencing technique. The jet apex of M 87 could be deduced at about 46 $\mu$as upstream of the 43 GHz core from core-shift measurements. The est…
Jet launching from merging magnetized binary neutron stars with realistic equations of state
2021
We perform general relativistic, magnetohydrodynamic (GRMHD) simulations of binary neutron stars in quasi-circular orbit that merge and undergo delayed or prompt collapse to a black hole (BH). The stars are irrotational and modeled using an SLy or an H4 nuclear equation of state. To assess the impact of the initial magnetic field configuration on jet launching, we endow the stars with a purely poloidal magnetic field that is initially unimportant dynamically and is either confined to the stellar interior or extends from the interior into the exterior as in typical pulsars. Consistent with our previous results, we find that only the BH + disk remnants originating from binaries that form hype…