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Search Results: 1 - 10 of 141512 matches for " O. Gonzalez-Martin "
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X-ray variability of 104 active galactic nuclei. XMM-Newton power-spectrum density profiles
O. Gonzalez-Martin,S. Vaughan
Physics , 2012, DOI: 10.1051/0004-6361/201219008
Abstract: AGN, powered by accretion onto SMBHs, are thought to be scaled up versions of Galactic black hole X-ray binaries (BH-XRBs). In the past few years evidence of such correspondence include similarities in the broadband shape of the X-ray variability power spectra, with characteristic bend times-scales scaling with mass. We have performed a uniform analysis of the power spectrum densities (PSDs) of 104 nearby (z<0.4) AGN using 209 XMM-Newton/pn observations. The PSDs have been estimated in three energy bands: 0.2-10, 0.2-2, and 2-10 keV. The sample comprises 61 Type-1 AGN, 21 Type-2 AGN, 15 NLSy1, and 7 BLLACS. We have fitted each PSD to two models: (1) a single power-law model and (2) a bending power-law model. Among the entire sample, 72% show significant variability in at least one of the three bands tested. A high percentage of low-luminosity AGN do not show any significant variability. The PSD of the majority of the variable AGN was well described by a simple power-law with a mean index of 2. In 15 sources we found that the bending power law model was preferred with a mean slope of 3 and a mean bend frequency of 2.E-04 Hz. Only KUG1031+398 (REJ1034+396) shows evidence for quasi-periodic oscillations. The `fundamental plane' relating variability timescale, black hole mass, and luminosity is demonstrated using the new X-ray timing results presented here together with a compilation of the previously detected timescales from the literature. Both quantitative (i.e. scaling with BH mass) and qualitative (overall PSD shapes) found in this sample of AGN are in agreement with the expectations for the SMBHs and BH-XRBs being the same phenomenon scaled-up with the size of the BH. The steep PSD slopes above the high frequency bend bear a closer resemblance to those of the `soft/thermal dominated' BH-XRB states than other states.
Fitting LINER nuclei within the AGN family: A matter of obscuration?
O. Gonzalez-Martin,J. Masegosa,I. Marquez,M. Guainazzi
Physics , 2009, DOI: 10.1088/0004-637X/704/2/1570
Abstract: In this paper we study the nuclear obscuration of galaxies hosting LINERs based on their X-ray and optical emission. They show column densities (N_H) at soft energies (0.5-2 keV) mostly related to the diffuse emission around the AGN, showing a correlation with the optical extinction. N_H at hard energies (2-10 keV) seem to be much higher than what would be expected from the optical extinction. They might be associated to the inner regions of the AGN, buried at optical wavelengths. The main result of this paper is that around 50% of our LINER sample shows signatures of Compton-thickness (CT) according to the most common tracers: the X-ray spectral index, F(2-10 keV)/F([OIII]) ratio and EW(FeKa). However, the EWs of CT LINERs are significantly lower than in CT Sy, suggesting that the 2-10 keV emission is dominated by electron scattering of the otherwise invisible AGN, or by emission from shocked gas associated to star formation rather than by reflection from the inner wall of the torus. However, no clear relation seems to exist between galaxies with optical dust lanes and X-ray classified CT objects. This may suggest that CT sources should be related to absorbing material located at the very inner regions of the AGN, maybe in the putative dusty torus. Larger M_BH and lower Eddington ratios than Sy galaxies have been found. This effect can be better attributed to LINER nuclei being hosted by earlier morphological types than Sy nuclei. However, it has to be noted that, once a proper correction to the X-ray luminosity is applied, LINERs show Eddington ratios overlapping those of Sy 2. We speculate with a possible scenario for LINER nuclei: an inner obscuring matter similar to that of Sy 2, and an external obscuring matter responsible for the optical extinction. CT sources appear to be more common among LINERs than Sy.
The scaling of X-ray variability with luminosity in Ultra-luminous X-ray sources
O. Gonzalez-Martin,I. Papadakis,P. Reig,A. Zezas
Physics , 2010, DOI: 10.1051/0004-6361/201014564
Abstract: We investigated the relationship between the X-ray variability amplitude and X-ray luminosity for a sample of 14 bright Ultra-luminous X-ray sources (ULXs) with XMM-Newton/EPIC data, and compare it with the well established similar relationship for Active Galactic Nuclei (AGN). We computed the normalised excess variance in the 2-10 keV light curves of these objects and their 2-10 keV band intrinsic luminosity. We also determined model "variability-luminosity" relationships for AGN, under several assumptions regarding their power-spectral shape. We compared these model predictions at low luminosities with the ULX data. The variability amplitude of the ULXs is significantly smaller than that expected from a simple extrapolation of the AGN "variability-luminosity" relationship at low luminosities. We also find evidence for an anti-correlation between the variability amplitude and L(2-10 keV) for ULXs. The shape of this relationship is consistent with the AGN data but only if the ULXs data are shifted by four orders of magnitudes in luminosity. Most (but not all) of the ULXs could be "scaled-down" version of AGN if we assume that: i) their black hole mass and accretion rate are of the order of ~(2.5-30)x 10E+03 Msolar and ~ 1-80 % of the Eddington limit, and ii) their Power Spectral Density has a doubly broken power-law shape. This PDS shape and accretion rate is consistent with Galactic black hole systems operating in their so-called "low-hard" and "very-high" states.
A bright radio HH object with large proper motions in the massive star-forming region W75N
C. Carrasco-Gonzalez,L. F. Rodriguez,J. M. Torrelles,G. Anglada,O. Gonzalez-Martin
Physics , 2010, DOI: 10.1088/0004-6256/139/6/2433
Abstract: We analyze radio continuum and line observations from the archives of the Very Large Array, as well as X-ray observations from the \emph{Chandra} archive of the region of massive star formation W75N. Five radio continuum sources are detected: VLA 1, VLA 2, VLA 3, Bc, and VLA 4. VLA 3 appears to be a radio jet; we detect J=1-0, v=0 SiO emission towards it, probably tracing the inner parts of a molecular outflow. The radio continuum source Bc, previously believed to be tracing an independent star, is found to exhibit important changes in total flux density, morphology, and position. These results suggest that source Bc is actually a radio Herbig-Haro object, one of the brightest known, powered by the VLA~3 jet source. VLA 4 is a new radio continuum component, located a few arcsec to the south of the group of previously known radio sources. Strong and broad (1,1) and (2,2) ammonia emission is detected from the region containing the radio sources VLA~1, VLA~2, and VLA~3. Finally, the 2-10 keV emission seen in the \emph{Chandra}/ACIS image shows two regions that could be the termination shocks of the outflows from the multiple sources observed in W75N.
An X-ray view of 82 LINERs with Chandra and XMM-Newton data
O. Gonzalez-Martin,J. Masegosa,I. Marquez,M. Guainazzi,E. Jimenez-Bailon
Physics , 2009, DOI: 10.1051/0004-6361/200912288
Abstract: We present the results of an homogeneous X-ray analysis for 82 nearby LINERs selected from the catalogue of Carrillo et al. (1999). All sources have available Chandra (68 sources) and/or XMM-Newton (55 sources) observations. This is the largest sample of LINERs with X-ray spectral data (60 out of the 82 objects) and significantly improves our previous analysis based on Chandra data for 51 LINERs (Gonzalez-Martin et al. 2006). It increases both the sample size and adds XMM-Newton data. New models permit the inclusion of double absorbers in the spectral fits. Nuclear X-ray morphology is inferred from the compactness of detected nuclear sources in the hard band (4.5-8.0 keV). Sixty per cent of the sample shows a compact nuclear source and are classified as AGN candidates. The spectral analysis indicates that best fits involve a composite model: absorbed primary continuum and (2) soft spectrum below 2 keV described by an absorbed scatterer and/or a thermal component. The resulting median spectra parameters and their standard deviations are: G=2.11, =0.54 keV, =21.32 and =21.93. We complement our X-ray results with our analysis of HST optical images and literature data on emission lines, radio compactness and stellar population. Adding all these multiwavelength data, we conclude that evidence do exist supporting the AGN nature of their nuclear engine for 80% of the sample (66 out of 82 objects).
The silicate absorption profile in the ISM towards the heavily obscured nucleus of NGC 4418
P. F. Roche,A. Alonso-Herrero,O. Gonzalez-Martin
Physics , 2015, DOI: 10.1093/mnras/stv495
Abstract: The 9.7-micron silicate absorption profile in the interstellar medium provides important information on the physical and chemical composition of interstellar dust grains. Measurements in the Milky Way have shown that the profile in the diffuse interstellar medium is very similar to the amorphous silicate profiles found in circumstellar dust shells around late M stars, and narrower than the silicate profile in denser star-forming regions. Here, we investigate the silicate absorption profile towards the very heavily obscured nucleus of NGC 4418, the galaxy with the deepest known silicate absorption feature, and compare it to the profiles seen in the Milky Way. Comparison between the 8-13 micron spectrum obtained with TReCS on Gemini and the larger aperture spectrum obtained from the Spitzer archive indicates that the former isolates the nuclear emission, while Spitzer detects low surface brightness circumnuclear diffuse emission in addition. The silicate absorption profile towards the nucleus is very similar to that in the diffuse ISM in the Milky Way with no evidence of spectral structure from crystalline silicates or silicon carbide grains.
The soft X-ray and narrow-line emission of Mrk573 on kiloparcec scales
O. Gonzalez-Martin,J. A. Acosta-Pulido,A. M. Perez Garcia,C. Ramos Almeida
Physics , 2010, DOI: 10.1088/0004-637X/723/2/1748
Abstract: We present a study of the circumnuclear region of the nearby Seyfert galaxy Mrk573 using Chandra, XMM-Newton and HST data. The X-ray morphology shows a biconical region extending up to 12 arcsecs (4 kpc) in projection from the nucleus. A strong correlation between the X-rays and the highly ionized gas seen in the [O III] image is reported. Moreover, we have studied the line intensities detected with the RGS/XMM-Newton and used them to fit the low resolution EPIC/XMM-Newton and ACIS/Chandra spectra. The RGS spectrum is dominated by emission lines of C VI, O VII, O VIII, Fe XVII, and Ne IX, among others. A good fit is obtained using these emission lines found in the RGS spectrum as a template for Chandra spectra of the nucleus and extended emission. The photoionization model Cloudy provides a reasonable fit for both the nuclear region and the cone-like structures. For the nucleus the emission is modelled using two phases: a high ionization [log(U)=1.23] and a low ionization [log(U)=0.13]. For the high ionization phase the transmitted and reflected component are in a ratio 1:2, whereas for the low ionization the reflected component dominates. For the extended emission, we successfully reproduced the emission with two phases. The first phase shows a higher ionization parameter for the NW (log(U)=0.9) than for the SE cone (log(U)=0.3). The second phase shows a low ionization parameter (log(U)=-3) and is rather uniform for NW and SE cones. In addition, the nuclear optical/infrared SED has been modeled by a clumpy torus model. The torus bolometric luminosity agrees with the AGN luminosity inferred from the observed hard X-ray spectrum. The optical depth along the line of sight derived from the SED fit indicates a high neutral column density in agreement with the classification of the nucleus as a Compton-thick AGN.
The central parsecs of M87: jet emission and an elusive accretion disc
M. A. Prieto,J. A. Fernandez-Ontiveros,S. Markoff,D. Espada,O. Gonzalez-Martin
Physics , 2015,
Abstract: We present the first time-simultaneous high angular resolution spectral energy distribution (SED) of the core of M87 at a scale of 0.4 arcsecs across the electromagnetic spectrum. Two activity periods of the core of M87 are sampled: a quiescent mode, representative of the most common state of M87, and an active one, represented by the outburst occurring in 2005. The main difference between both SEDs is a shift in flux in the active SED by a factor of about two, their shapes remaining similar across the entire spectrum. The shape of the compiled SEDs is remarkably different from those of active galactic nuclei (AGN). It lacks three major AGN features: the IR bump, the inflection point at about 1 micron and the blue bump. The SEDs also differ from the spectrum of a radiatively inefficient accretion flow. Down to the scales of ~12 pc from the centre, we find that the emission from a jet gives an excellent representation of the spectrum over ten orders of magnitude in frequency for both the active and the quiescent phases of M87. The inferred total jet power is one to two orders of magnitude lower than the jet mechanical energy inferred from various methods in the literature. This discrepancy cannot easily be ascribed to variability. Yet, our measurements regard the inner few parsecs which might provide a genuine account of the jet power at the base. We derive a strict upper limit to the accretion rate of 6 x 10E-5 Mo / yr, assuming 10% efficiency. The inferred accretion power can account for M87 radiative luminosity at the jet-frame assuming boosting factors larger than 10, it is however two orders of magnitude below that required to account for M87 jet kinetic power. We thus propose that energy tapped from the black hole spin may be a complementary source to power the jet of M87, a large supply of accreting gas becoming thus unnecessary.
Binding Energies of the Alpha Particle and the A=3 Isobars from a Theoretical Geometric Model
Gustavo R. Gonzalez-Martin
Physics , 2008,
Abstract: We assume a triple geometric structure for the electromagnetic nuclear interaction. This nuclear electromagnetism is used to calculate the binding energies of the alpha particle and the A=3 isobar nuclides. The approximation for the resultant wave equation which lead to the deuteron binding energy from the modified Mathieu equation for the radial eigenvalue equation also establishes proton-electron-proton magnetic bonds in these nuclides and determines their binding energies. Completely theoretical calculations give 28.5 Mev., 7.64 Mev. and 8.42 Mev. for the binding energies of the alpha particle, the helium 3 isotope and tritium respectively. These values admit correction factors due to the approximations made.
Lepton and meson masses
Gustavo R. Gonzalez-Martin
Physics , 2004,
Abstract: The lepton mass ratios are calculated using a geometric unified theory, taking the leptons as the only three possible families of topological excitations of the electron or the neutrino. The theoretical results give 107.5916 Mev for the muon mass and 1770.3 Mev for the tau mass using the mass ratios. Using the additional geometric interaction energy in a muon-neutrino system, the main leptonic mass contribution to the pion and kaon mass is calculated to be, respectively, 140.88 Mev and 494.76 Mev. The necessary first order corrections, due to the interaction of the excitations, should be of the order of the discrepancies with experimental values. The three geometric families of leptonic excitations may be related to a quark structure.
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