Search results for "spectrum"
showing 10 items of 2043 documents
Multi-frequency observations of SWIFT J1626.6-5156
2011
SWIFT J1626.6-5156 is an X-ray pulsar that was discovered in December 2005 during an X-ray outburst. Although the X-ray data suggest that the system is a high-mass X-ray binary, very little information exists on the nature of the optical counterpart. We have analysed all RXTE observations since its discovery, archived optical spectroscopic and photometric data and obtained for the first time near-IR spectra. The K-band spectrum shows HeI 20581 A and HI 21660 A (Brackett-gamma) in emission, which confine the spectral type of the companion to be earlier than B2.5. The H-band spectrum exhibits the HI Br-18-11 recombination series in emission. The most prominent feature of the optical band spec…
Absorption by black hole remnants in metric-affine gravity
2019
Using numerical methods, we investigate the absorption properties of a family of nonsingular solutions {which arise in different metric-affine theories, such as quadratic and Born-Infeld gravity.} These solutions continuously interpolate between Schwarzschild black holes and naked solitons with wormhole topology. The resulting spectrum is characterized by a series of quasibound states excitations, associated with the existence of a stable photonsphere.
A relativistically smeared spectrum in the neutron star X-ray binary 4U 1705−44: looking at the inner accretion disc with X-ray spectroscopy
2009
Iron emission lines at 6.4-6.97 keV, identified with fluorescent Kalpha transitions, are among the strongest discrete features in the X-ray band. These are therefore one of the most powerful probes to infer the properties of the plasma in the innermost part of the accretion disc around a compact object. In this paper we present a recent XMM observation of the X-ray burster 4U 1705-44, where we clearly detect a relativistically smeared iron line at about 6.7 keV, testifying with high statistical significance that the line profile is distorted by high velocity motion in the accretion disc. As expected from disc reflection models, we also find a significant absorption edge at about 8.3 keV; th…
Measurement of the cosmic ray energy spectrum with IceTop-73
2013
Physical review / D 88(4), 042004 (2013). doi:10.1103/PhysRevD.88.042004
On the flavor composition of the high-energy neutrinos in IceCube
2016
The IceCube experiment has recently released 3 years of data of the first ever detected high-energy (>30 TeV) neutrinos, which are consistent with an extraterrestrial origin. In this talk, we compute the compatibility of the observed track-to-shower ratio with possible combinations of neutrino flavors with relative proportion (alpha_e:alpha_mu:alpha_tau). Although this observation is naively favored for the canonical (1:1:1) at Earth, once we consider the IceCube expectations for the atmospheric muon and neutrino backgrounds, this flavor combination presents some tension with data. We find that, for an astrophysical neutrino E_nu^{-2} energy spectrum, (1:1:1) at Earth is currently disfav…
X-ray spectroscopy of MXB 1728-34 with XMM-Newton
2011
We have analysed an XMM-Newton observation of the low mass X-ray binary and atoll source MXB 1728-34. The source was in a low luminosity state during the XMM-Newton observation, corresponding to a bolometric X-ray luminosity of 5*10E36 d^2 erg/s, where d is the distance in units of 5.1 kpc. The 1-11 keV X-ray spectrum of the source, obtained combining data from all the five instruments on-board XMM-Newton, is well fitted by a Comptonized continuum. Evident residuals are present at 6-7 keV which are ascribed to the presence of a broad iron emission line. This feature can be equally well fitted by a relativistically smeared line or by a self-consistent, relativistically smeared, reflection mo…
Testing Rate Dependent corrections on timing mode EPIC-pn spectra of the accreting Neutron Star GX 13+1
2014
When the EPIC-pn instrument on board XMM-Newton is operated in Timing mode, high count rates (>100 cts/s) of bright sources may affect the calibration of the energy scale, resulting in a modification of the real spectral shape. The corrections related to this effect are then strongly important in the study of the spectral properties. Tests of these calibrations are more suitable in sources which spectra are characterised by a large number of discrete features. Therefore, in this work, we carried out a spectral analysis of the accreting Neutron Star GX 13+1, which is a dipping source with several narrow absorption lines and a broad emission line in its spectrum. We tested two different co…
Hydrodynamic simulations unravel the progenitor-supernova-remnant connection in SN 1987A
2019
(Abridged) We aim at linking the dynamical and radiative properties of the remnant of SN 1987A to the geometrical and physical characteristics of the parent aspherical SN explosion and to the internal structure of its progenitor star. We performed 3D hydrodynamic simulations which describe the long-term evolution of SN 1987A from the onset of the SN to the full-fledged remnant at the age of 50 years, accounting for the pre-SN structure of the progenitor star. The simulations include all physical processes relevant for the complex phases of SN evolution and for the interaction of the SNR with the highly inhomogeneous ambient environment around SN 1987A. From the simulations, we synthesize ob…
Enhanced local-type inflationary trispectrum from a non-vacuum initial state
2011
We compute the primordial trispectrum for curvature perturbations produced during cosmic inflation in models with standard kinetic terms, when the initial quantum state is not necessarily the vacuum state. The presence of initial perturbations enhances the trispectrum amplitude for configuration in which one of the momenta, say $k_3$, is much smaller than the others, $k_3 \ll k_{1,2,4}$. For those squeezed configurations the trispectrum acquires the so-called local form, with a scale dependent amplitude that can get values of order $ \epsilon ({k_1}/{k_3})^2$. This amplitude can be larger than the prediction of the so-called Maldacena consistency relation by a factor $10^6$, and can reach t…
Semiclassical geons at particle accelerators
2014
We point out that in certain four-dimensional extensions of general relativity constructed within the Palatini formalism stable self-gravitating objects with a discrete mass and charge spectrum may exist. The incorporation of nonlinearities in the electromagnetic field may effectively reduce their mass spectrum by many orders of magnitude. As a consequence, these objects could be within (or near) the reach of current particle accelerators. We provide an exactly solvable model to support this idea.