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Search Results: 1 - 10 of 200732 matches for " P. Reig "
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Spectral states in Be/X-ray pulsars
E. Nespoli,P. Reig
Physics , 2013,
Abstract: In the last quarter of a century, a unified characterization of the spectral evolution of low-mass X-ray binaries, both containing a neutron star and a black hole, was possible. In this context, the notion of source states characterizing the X-ray emission from black-hole binaries and neutron-star low-mass X-ray binaries revealed to be a very useful tool to disentangle the complex spectral and aperiodic phenomenology displayed by those classes of accreting objects. Be/X-ray binaries constitute another major class of transient accreting binaries, for which very little work has been done on the correlated timing and spectral variability. Especially, no definition of source states exists for this class, in spite of their highly variable X-ray emission. When active, Be/X-ray binaries are among the brightest objects in the X-ray sky and are characterized by dramatic variability in brightness on timescales ranging from seconds to years. It is then worth it to ask whether a definition of spectral states is possible for these systems. In this work, we try to address such a question, investigating whether accreting X-ray pulsars display source states and characterizing those states through their spectral properties. Our results show that Be/X-ray pulsars trace two different branches in their hardness-intensity diagram: the horizontal branch, a low-intensity state, and the diagonal branch, a high-intensity state that only appears when the X-ray luminosity exceeds a critical limit. We propose that the two branches are the phenomenological signature of two different accretion modes -- in agreement with recently proposed models -- depending on whether the luminosity of the source is above or below a critical value.
Discovery of X-ray pulsations in the Be/X-ray binary IGR J21343+4738
P. Reig,A. Zezas
Physics , 2014, DOI: 10.1093/mnras/stu898
Abstract: We report on the discovery of X-ray pulsations in the Be/X-ray binary IGR J21343+4738 during an XMM-Newton observation. We obtained a barycentric corrected pulse period of 320.35+-0.06 seconds. The pulse profile displays a peak at low energy that flattens at high energy. The pulse fraction is 45+-3$% and independent of energy within the statistical uncertainties. The 0.2-12 keV spectrum is well fit by a two component model consisting of a blackbody with kT=0.11+-0.01 keV and a power law with photon index Gamma=1.02+-0.07. Both components are affected by photoelectric absorption with a equivalent hydrogen column density NH=(1.08+-0.15)x 10^{22} cm^{-2} The observed unabsorbed flux is 1.4x10^{-11} erg cm^{-2} s^{-1} in the 0.2-12 keV energy band. Despite the fact that the Be star's circumstellar disc has almost vanished, accretion continues to be the main source of high energy radiation. We argue that the observed X-ray luminosity (LX~10^{35} erg s^{-1}) may result from accretion via a low-velocity equatorial wind from the optical companion.
Disc-loss episode in the Be shell optical counterpart to the high-mass X-ray binary IGR J21343+4738
P. Reig,A. Zezas
Physics , 2013, DOI: 10.1051/0004-6361/201321408
Abstract: The main goal of this work is to determine the properties of the optical counterpart to the INTEGRAL source IGR J21343+4738, and study its long-term optical variability. We present optical photometric BVRI and spectroscopic observations covering the wavelength band 4000-7500 A. We find that the optical counterpart to IGR J21343+4738 is a V=14.1 B1IVe shell star located at a distance of ~8.5 kpc. The Halpha line changed from an absorption dominated profile to an emission dominated profile, and then back again into absorption. In addition, fast V/R asymmetries were observed once the disc developed. Although the Balmer lines are the most strongly affected by shell absorption, we find that shell characteristics are also observed in He I lines. The optical spectral variability of IGR J21343+4738 is attributed to the formation of an equatorial disc around the Be star and the development of an enhanced density perturbation that revolves inside the disc. We have witnessed the formation and dissipation of the circumstellar disc. The strong shell profile of the Halpha and He I lines and the fact that no transition from shell phase to a pure emission phase is seen imply that we are seeing the system near edge-on.
Long-term variability of high-mass X-ray binaries. I.Photometry
P. Reig,J. Fabregat
Physics , 2014, DOI: 10.1051/0004-6361/201425008
Abstract: We present photometric observations of the field around the optical counterparts of high-mass X-ray binaries. Our aim is to study the long-term photometric variability in correlation with their X-ray activity and derive a set of secondary standard stars that can be used for time series analysis. We find that the donors in Be/X-ray binaries exhibit larger amplitude changes in the magnitudes and colours than those hosting a supergiant companion. The amplitude of variability increases with wavelength in Be/X-ray binaries and remains fairly constant in supergiant systems. When time scales of years are considered, a good correlation between the X-ray and optical variability is observed. The X-rays cease when optical brightness decreases. These results reflect the fact that the circumstellar disk in Be/X-ray binaries is the main source of both optical and X-ray variability. We also derive the colour excess, E(B-V), selecting data at times when the contribution of the circumstellar disk was supposed to be at minimum, and we revisit the distance estimates.
A jet model for Galactic black-hole X-ray sources: the cutoff energy-phase-lag correlation
P. Reig,N. Kylafis
Physics , 2015,
Abstract: Galactic black-hole X-ray binaries emit a compact, optically thick, mildy relativistic radio jet when they are in the hard and hard-intermediate states. In a series of papers, we have developed a jet model and have shown, through Monte Carlo simulations, that our model can explain many observational results. In this work, we investigate one more constraining relationship between the cutoff energy and the phase lag during the early stages of an X-ray outburst of the black-hole X-ray binary GX 339-4: the cutoff energy decreases while the phase lag increases during the brightening of the hard state. We demonstrate that our jet model naturally explains the above correlation, with a minor modification consisting of introducing an acceleration zone at the base of the jet. The observed correlation between the cutoff energy and the phase lag suggests that the lags are produced by the hard component. Here we show that this correlation arises naturally if Comptonization in the jet produces these two quantities.
Accreting magnetars: a new type of high-mass X-ray binaries?
P. Reig,J. M. Torrejon,P. Blay
Physics , 2012, DOI: 10.1111/j.1365-2966.2012.21509.x
Abstract: The discovery of very slow pulsations (Pspin=5560s) has solved the long-standing question of the nature of the compact object in the high-mass X-ray binary 4U 2206+54 but has posed new ones. According to spin evolutionary models in close binary systems, such slow pulsations require a neutron star magnetic field strength larger that the quantum critical value, suggesting the presence of a magnetar. We present the first XMM-Newton observations of 4U 2206+54 and investigate its spin evolution. We find that the observed spin-down rate agrees with the magnetar scenario. We analyse ISGRI/INTEGRAL observations of 4U 2206+54 to search for the previously suggested cyclotron resonance scattering feature at ~30 keV. We do not find a clear indication of the presence of the line, although certain spectra display shallow dips, not always at 30 keV. The association of these dips with a cyclotron line is very dubious because of its apparent transient nature. We also investigate the energy spectrum of 4U 2206+54 in the energy range 0.3-10 keV with unprecedented detail and report for the first time the detection of very weak 6.5 keV fluorescence iron lines. The photoelectric absorption is consistent with the interstellar value, indicating very small amount of local matter, which would explain the weakness of the florescence lines. The lack of matter locally to the source may be the consequence of the relatively large orbital separation of the two components of the binary. The wind would be too tenuous in the vicinity of the neutron star.
La vida universitaria y el plan bolonia: Retrato de dos generaciones estudiantiles
Feixa Pàmpols,Carles; Campanera Reig,Mireia;
Utopìa y Praxis Latinoamericana , 2010,
Abstract: the aim of this study is to understand the vision that students at the university of lleida (catalonia, spain) have regarding the university and the city where they spend some essential years of their lives. after a prologue that evokes the recent student movement against the so-called bologna plan, the study outlines a historical and theoretical context about studies of university youth, the methodology utilized is justified, and some data about the local context are expounded. next, the study analyzes the student condition as it is experienced by youth beginning a career (academic and vital) in the university of lleida. the main part of the study focuses on an overview of the spaces and times of their daily lives, listening to what they have to say about the university, its residential and urban areas, as well as their times for study, sociability and recreation, including an assessment of the implementation of new degrees. lastly, visions about the city and the university are approached, including those coming from local students (from lleida) as well as those from students in other catalan cities and other countries. some conclusive remarks are made comparing the university generations of 2000 and 2010.
La vida universitaria y el Plan Bolonia: retrato de dos generaciones estudiantiles
Carles Feixa Pàmpols,Mireia Campanera Reig
Utopia y Praxis Latinoamericana , 2010,
Abstract: La pretensión de este artículo es captar las visiones que los y las estudiantes de la Universidad de Lleida (Catalu a, Espa a) tienen sobre la universidad y la ciudad donde pasan unos a os primordiales en su vida. Tras un prólogo donde evocamos el recientemovimiento estudiantil contra el denominado Plan Bolonia, esbozamos un marco histórico y teórico sobre los estudios a la juventud universitaria, justificamos la metodología utilizada, y exponemos algunos datos sobre el contexto local.Acontinuación analizamos la condición estudiantil tal como es vivida por los jóvenes que inician una carrera (académica y vital) en la Universidad de Lleida. La parte central del estudio se centra en un recorrido por los espacios y los tiempos de su vida cotidiana, escuchando lo que nos dicen de los espacios universitarios, residenciales y urbanos, y de los tiempos de estudio, sociabilidad y fiesta. Al final abordamos las visiones sobre la ciudad, tanto de los estudiantes locales como de los provenientes de otras localidades catalanas y de otros países, acabando con unas reflexiones conclusivas donde comparamos dos generaciones estudiantiles: la del 2000 y la de 2010.
New insights into the Be/X-ray binary system MXB 0656-072
E. Nespoli,P. Reig,A. Zezas
Physics , 2012, DOI: 10.1051/0004-6361/201219586
Abstract: The X-ray transient MXB 0656-072 is a poorly studied member of high-mass X-ray binaries. Based on the transient nature of the X-ray emission, the detection of pulsations, and the early-type companion, it has been classified as a Be X-ray binary (Be/XRB). However, the flaring activity covering a large fraction of a giant outburst is somehow peculiar. Our goal is to investigate the multiwavelength variability of the high-mass X-ray binary MXB 0656-072. We carried out optical spectroscopy and analysed all RXTE archive data, performing a detailed X-ray-colour, spectral, and timing analysis of both normal (type-I) and giant (type-II) outbursts from MXB 0656-072 This is the first detailed analysis of the optical counterpart in the classification region (4000-5000 A). From the strength and ratio of the elements and ions, we derive an O9.5Ve spectral type, in agreement with previous classification. This confirms its Be nature. The characterisation of the Be/XRB system relies on Balmer lines in emission in the optical spectra, long-term X-ray variability, and the orbital period vs. spin period and EW(H\alpha) relation. The peculiar feature that distinguishes the type-II outburst is flaring activity, which occurs during the whole outburst peak, before a smoother decay. We interpret it in terms of magneto-hydrodynamic instability. Colour and spectral analysis reveal a hardening of the spectrum as the flux increases. We explored the aperiodic X-ray variability of the system for the first time, finding a correlation of the central frequency and rms of the main timing component with luminosity, which extends up to a "saturation" flux of 1E-8 erg/cm^2/s. A correlation between timing and spectral parameters was also found, pointing to an interconnection between the two physical regions responsible for both phenomenologies.
Aperiodic variability of low-mass X-ray binaries at very low frequencies
P. Reig,I. Papadakis,N. D. Kylafis
Physics , 2002, DOI: 10.1051/0004-6361:20021693
Abstract: We have obtained discrete Fourier power spectra of a sample of persistent low-mass neutron-star X-ray binaries using long-term light curves from the All Sky Monitor on board the Rossi X-ray Timing Explorer. Our aim is to investigate their aperiodic variability at frequencies in the range 1 x 10^{-7}-5 x 10^{-6} Hz and compare their properties with those of the black-hole source Cyg X-1. We find that the classification scheme that divides LMXBs into Z and atoll sources blurs at very low frequencies. Based on the long-term (~ years) pattern of variability and the results of power-law fits (P ~ v^{-a}) to the 1 x 10^{-7}-5 x 10^{-6} Hz power density spectra, low-mass neutron-star binaries fall into three categories. Type I includes all Z sources, except Cyg X-2, and the atoll sources GX9+1 and GX13+1. They show relatively flat power spectra (a < 0.9) and low variability (rms < 20%). Type II systems comprise 4U 1636-53, 4U 1735-44 and GX3+1. They are more variable (20% < rms < 30%) and display steeper power spectra (0.9 < a < 1.2) than Type I sources. Type III systems are the most variable (rms > 30%) and exhibit the steepest power spectra (a > 1.2). The sources 4U 1705-44, GX354-0 and 4U 1820-30 belong to this group. GX9+9 and Cyg X-2 appear as intermediate systems in between Type I and II and Type II and III sources, respectively. We speculate that the differences in these systems may be caused by the presence of different types of mass-donor companions. Other factors, like the size of the accretion disc and/or the presence of weak magnetic fields, are also expected to affect their low-frequency X-ray aperiodic varibility.
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