Search results for "continuum"
showing 10 items of 477 documents
Does GRS 1915+105 exhibit "canonical" black-hole states?
2003
We have analysed RXTE data of the superluminal source GRS 1915+105 in order to investigate if, despite its extreme variability, it also exhibits the canonical source states that characterise other black-hole candidates. The phenomenology of GRS 1915+105 has been described in terms of three states (named A, B and C) based on their hardness ratios and position in the colour-colour diagram. We have investigated the connection between these states and the canonical behaviour and found that the shape of the power spectral continuum and the values of the best-fit model parameters to the noise components in all three states indicate that the source shows properties similar to the canonical very hi…
On Anomaly-Free Dark Matter Models
2019
We investigate the predictions of anomaly-free dark matter models for direct and indirect detection experiments. We focus on gauge theories where the existence of a fermionic dark matter candidate is predicted by anomaly cancellation, its mass is defined by the new symmetry breaking scale, and its stability is guaranteed by a remnant symmetry after the breaking of the gauge symmetry. We find an upper bound on the symmetry breaking scale by applying the relic density and perturbative constraints. The anomaly-free property of the theories allows us to perform a full study of the gamma lines from dark matter annihilation. We investigate the correlation between predictions for final-state radia…
Attractive ion-ion correlation forces and the dielectric approximation.
2016
We analyze the classical problem of the interaction between two charged surfaces separated by a solution containing neutralizing counter-ions. The focus is on obtaining a description where the solvent is treated explicitly rather than through a dielectric approximation as is conventionally done. We summarize the results of three papers where we have used a Stockmayer fluid model in Monte Carlo simulations. It is shown that the attractive ion-ion correlation mechanism is also operating when the solvent is described explicitly. There appears an oscillatory component to the force, but when this is accounted for, there is a semi-quantitative agreement between the continuum model and the model w…
High Resolution Spectroscopy of 4U 1728-34 from a Simultaneous Chandra-RXTE Observation
2004
We report on a simultaneous Chandra and RossiXTE observation of the LMXB atoll bursting source 4U 1728-34 performed on 2002 March 3-5. We fitted the 1.2-35 keV continuum spectrum with a blackbody plus a Comptonized component. An overabundance of Si by a factor of ~2 with respect to Solar abundance is required for a satisfactory fit. Large residuals at 6-10 keV can be fitted by a broad (FWHM ~ 1.6 keV) Gaussian emission line, or, alternatively, by absorption edges associated with Fe I and Fe XXV at ~7.1 keV and ~9 keV, respectively. In this interpretation, we find no evidence of a broad, or narrow Fe Kalpha line, between 6 and 7 keV. We tested our alternative modeling of the iron Kalpha regi…
Detection of a Hard Tail in the X-Ray Spectrum of the Z Source GX 349+2
2001
We present the results of a BeppoSAX observation of the Z source GX 349+2 covering the energy range 0.1-200 keV. The presence of flares in the light curve indicates that the source was in the flaring branch during the BeppoSAX observation. We accumulated energy spectra separately for the non-flaring intervals and the flares. In both cases the continuum is well described by a soft blackbody ($k T_{BB} \sim 0.5$ keV) and a Comptonized spectrum corresponding to an electron temperature of $k T_e \sim 2.7$ keV, optical depth $\tau \sim 10$ (for a spherical geometry), and seed photon temperature of $k T_W \sim 1$ keV. All temperatures tend to increase during the flares. In the non-flaring emissio…
Unveiling the spatial structure of the overionized plasma in the supernova remnant W49B
2011
W49B is a mixed-morphology supernova remnant with thermal X-ray emission dominated by the ejecta. In this remnant, the presence of overionized plasma has been directly established, with information about its spatial structure. However, the physical origin of the overionized plasma in W49B has not yet been understood. We investigate this intriguing issue through a 2D hydrodynamic model that takes into account, for the first time, the mixing of ejecta with the inhomogeneous circumstellar and interstellar medium, the thermal conduction, the radiative losses from optically thin plasma, and the deviations from equilibrium of ionization induced by plasma dynamics. The model was set up on the basi…
MICROLENSING OF QUASAR ULTRAVIOLET IRON EMISSION
2013
We measure the differential microlensing of the UV Fe II and Fe III emission line blends between 14 quasar image pairs in 13 gravitational lenses. We find that the UV iron emission is strongly microlensed in four cases with amplitudes comparable to that of the continuum. Statistically modeling the magnifications, we infer a typical size of r{sub s}∼4√(M/M{sub ⊙}) light-days for the Fe line-emitting regions, which is comparable to the size of the region generating the UV continuum (∼3-7 light-days). This may indicate that a significant part of the UV Fe II and Fe III emission originates in the quasar accretion disk.
The 0.1-100 keV Spectrum of LMC X-4 in the High State: Evidence for a High Energy Cyclotron Absorption Line
2001
We report on the spectral analysis of the X-ray pulsar LMC X-4 in its high state out of eclipse observed by BeppoSAX. During this observation no coherent pulsations are detected. The primary continuum is well described by a power law with a high energy cutoff (E_cutoff ~ E_fold ~ 18 keV). The addition of a cyclotron absorption line at ~100 keV improves the fit significantly. The inferred magnetic moment is 1.1 10^{31} Gauss cm^3, in agreement with the value estimated assuming that the neutron star is at the spin equilibrium, as it has been proposed for this source. The remaining excess at low energies can be fitted by a Comptonization of soft photons by moderately hot electrons (kT ~0.9 keV…
Be stars in open clusters. I. uvby $ ^{\bf \beta}$ photometry
1996
We present uvby β photometry for Be stars in eight open clusters and two OB associations. It is shown that Be stars occupy anomalous positions in the photometric diagrams, which can be explained in terms of the circumstellar continuum radiation contribution to the photometric indices. In the - M V plane Be stars appear redder than the non emission B stars, due to the additional reddening caused by the hydrogen free-bound and free-free recombination in the circumstellar envelope. In the c 0 - M V plane the earlier Be stars present lower c 0 values than absorption-line B stars, which is caused by emission in the Balmer discontinuity, while the later Be stars deviate towards higher c 0 values,…
BeppoSAX observation of 4U 1907+09: Detection of a cyclotron line and its second harmonic
2000
Abstract We report the detection of a cyclotron absorption line and its second harmonic in the average spectrum of the high mass X-ray binary 4U1907+09 observed by the BeppoSAX satellite. The broad band spectral capability of BeppoSAX allowed a good determination of the continuum against which the two absorption features are evident at ∼ 19 and ∼ 39 keV. Correcting for the gravitational redshift of a ∼ 1.4 M⊙ neutron star, the inferred surface magnetic field strength is Bsurf = 2.1 × 1012 G.