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Non-dipolar magnetic field at the polar cap of neutron stars and the physics of pulsar radiation
Andrzej Szary
Physics , 2013,
Abstract: Despite the fact that pulsars have been observed for almost half a century, many questions have remained unanswered. We use the analysis of X-ray observations in order to study the polar cap region of radio pulsars. The size of the hot spots implies that the magnetic field configuration just above the stellar surface differs significantly from a purely dipole one. We can estimate the surface magnetic field as of the order of $10^{14}\,{\rm G}$. On the other hand, the temperature of the hot spots is about a few million Kelvins. Based on these two facts the Partially Screened Gap (PSG) model was proposed to describe the Inner Acceleration Region (IAR). The PSG model assumes that the temperature of the actual polar cap is equal to the so-called critical value, i.e. the temperature at which the outflow of thermal ions from the surface screens the gap completely. We have found that, depending on the conditions above the polar cap, the generation of high energetic photons in IAR can be caused either by Curvature Radiation (CR) or by Inverse Compton Scattering (ICS). This results in two different scenarios of breaking the acceleration gap: the so-called PSG-off mode for CR-dominated gaps and the PSG-on mode ICS-dominated gaps. The existence of two different mechanisms of gap breakdown naturally explains the mode-changing and the pulse nulling. Furthermore, the mode changes of the IAR may explain the anti-correlation of radio and X-ray emission in very recent observations of PSR B0943+10 (Hermsen et al., 2013). Simultaneous analysis of X-ray and radio properties have allowed to develop a model which explains the drifting subpulse phenomenon. According to this model the drift takes place when the charge density in IAR differs from the Goldreich-Julian co-rotational density. The proposed model allows to verify both the radio drift parameters and X-ray efficiency of the observed pulsars.
Regiones ganadoras y regiones perdedoras en el retorno de la democracia en Chile: poderes locales y desequilibrios territoriales
Szary,Anne-Laure;
EURE (Santiago) , 1997, DOI: 10.4067/S0250-71611997007000004
Abstract: abstract the author discusses the regional policies implemented in chile since the 1960's, emphasizing the practices of the last governments, where an important process of transition has occurred in regional matters (aylwin, 1990-1994; frei, 1994- ). the analysis is centered on political and economical dimensions, allowing the author to propose a new definition on the fonctionning of the region in chile, in the frame of globalization processes, introducing a critical question on the traditional territorial equilibrium which is practiced today
Regiones ganadoras y regiones perdedoras en el retorno de la democracia en Chile: poderes locales y desequilibrios territoriales
Anne-Laure Szary
EURE (Santiago) , 1997,
Abstract: The author discusses the regional policies implemented in Chile since the 1960's, emphasizing the practices of the last governments, where an important process of transition has occurred in regional matters (Aylwin, 1990-1994; Frei, 1994- ). The analysis is centered on political and economical dimensions, allowing the author to propose a new definition on the fonctionning of the region in Chile, in the frame of globalization processes, introducing a critical question on the traditional territorial equilibrium which is practiced today
Ruralité, ethnicité et montagne :
Anne-Laure Amilhat-Szary
Revue de Géographie Alpine , 2009, DOI: 10.4000/rga.913
Abstract: Dans un contexte latinoaméricain où les populations autochtones ont d attendre la fin du XXème siècle pour regagner en visibilité, l’identité andine pose question. Dans cet article, l’analyse des étapes d’une mobilisation collective à base territoriale permet de suivre la redécouverte d’un ancrage identitaire longtemps nié ou refoulé du fait des conditions socio-politiques. L’affirmation retrouvée de l’ethnicité, voire de l’ andinité s’avère très complexe, comme le cas étudié, l’alliance Aymaras sin Fronteras (Aymaras sans frontières) le révèle. Dans ce cas, le processus de territorialisation se fonde sur une interaction dialectique entre ses composantes rurale, ethnique, et montagnarde (andine). In a Latin American context where indigenous populations have had to wait until the end of the XXth century to recover a certain visibility, the definition of Andean identity is still an issue. In this paper, an analysis of the various steps in a territorially based collective movement provides insights into this identity that was for so long denied or repressed on account of socio-political conditions. The possible re-assertion of “Andeanity” is very complex, as the case study of the “Aymaras Sin Fronteras” (Aymaras without borders) movement reveals. In this movement, the territorialisation process is based on the dialectics between its rural, ethnic and mountain (Andean) components.
Rurality, ethnicity and mountain areas:
Anne-Laure Amilhat-Szary
Revue de Géographie Alpine , 2009, DOI: 10.4000/rga.933
Abstract: In a Latin American context where indigenous populations have had to wait until the end of the XXth century to recover a certain visibility, the definition of Andean identity is still an issue. In this paper, an analysis of the various steps in a territorially based collective movement provides insights into this identity that was for so long denied or repressed on account of socio-political conditions. The possible re-assertion of “Andeanity” is very complex, as the case study of the “Aymaras Sin Fronteras” (Aymaras without borders) movement reveals. In this movement, the territorialisation process is based on the dialectics between its rural, ethnic and mountain (Andean) components. Dans un contexte latinoaméricain où les populations autochtones ont d attendre la fin du XXème siècle pour regagner en visibilité, l’identité andine pose question. Dans cet article, l’analyse des étapes d’une mobilisation collective à base territoriale permet de suivre la redécouverte d’un ancrage identitaire longtemps nié ou refoulé du fait des conditions socio-politiques. L’affirmation retrouvée de l’ethnicité, voire de l’ andinité s’avère très complexe, comme le cas étudié, l’alliance Aymaras sin Fronteras (Aymaras sans frontières) le révèle. Dans ce cas, le processus de territorialisation se fonde sur une interaction dialectique entre ses composantes rurale, ethnique, et montagnarde (andine).
Vortex stabilization in magnetic trilayer dots
P. Szary,O. Petracic,H. Zabel
Physics , 2009,
Abstract: The magnetization reversal and spin structure in circular Co/insulator/Ni80Fe20 trilayer dots has been investigated numerically. The effect of dipolar coupling between a soft ferromagnetic Permalloy (Py=Ni80Fe20) layer and a hard ferromagnetic Cobalt layer inside one stack is studied. We find either a stabilization or even a triggering of the vortex state in the Py layer due to the magnetic stray field of the Co layer, while the Co magnetization remains in a single-domain state. Furthermore, for thin Py layers a 360 deg-domain wall is observed. We construct a phase diagram, where regions of vortex stabilization, triggering, and occurrence of a 360 deg domain wall are marked.
Partially Screened Gap -- general approach and observational consequences
Andrzej Szary,George I. Melikidze,Janusz Gil
Physics , 2011,
Abstract: Observations of the thermal X-ray emission from radio pulsars implicate that the size of hot spots is much smaller then the size of the polar cap that follows from the purely dipolar geometry of pulsar magnetic field. Most plausible explanation of this phenomena is an assumption that the magnetic field at the stellar surface differs essentially from the purely dipolar field. We can determine magnetic field at the surface by the conservation of the magnetic flux through the area bounded by open magnetic field lines. Then the value of the surface magnetic field can be estimated as of the order of $10^{14}$ G. On the other hand observations show that the temperature of the hot spot is about a few million Kelvins. Based on these observations the Partially Screened Gap (PSG) model was proposed which assumes that the temperature of the actual polar cap (hot spot) equals to the so called critical temperature. We discuss correlation between the temperature and corresponding area of the thermal X-ray emission for a number of pulsars. The results of our analysis show that the PSG model is suitable to explain both cases: when the hot spot is smaller and larger then conventional polar cap. We argue that in the second case structure and curvature of field lines allow pair creation in the closed field lines region thus the secondary particles can heat the stellar surface outside the actual polar cap. We have found that the Curvature Radiation (CR) plays dominant role in avalanche pair production in the PSG. We studied dependence of the PSG parameters on the pulsar period, the magnetic field strength and the curvature of field lines.
On the Origin of Radio Emission from Magnetars
Andrzej Szary,George I. Melikidze,Janusz Gil
Physics , 2014, DOI: 10.1088/0004-637X/800/1/76
Abstract: Magnetars are the most magnetized objects in the known universe. Powered by the magnetic energy, and not by the rotational energy as in the case of radio pulsars, they have long been regarded as a completely different class of neutron stars. The discovery of pulsed radio emission from a few magnetars weakened the idea of a clean separation between magnetars and normal pulsars. We use the partially screened gap (PSG) model to explain radio emission of magnetars. The PSG model requires that the temperature of the polar cap is equal to the so-called critical value, i.e., the temperature at which the thermal ions outflowing from the stellar surface screen the acceleration gap. We show that a magnetar has to fulfill the temperature, power, and visibility conditions in order to emit radio waves. First, in order to form PSG, the residual temperature of the surface has to be lower than the critical value. Second, since the radio emission is powered by the rotational energy, it has to be high enough to enable heating of the polar cap by backstreaming particles to the critical temperature. Finally, the structure of the magnetic field has to be altered by magnetospheric currents in order to widen a radio beam and increase the probability of detection. Our approach allows us to predict whether a magnetar can emit radio waves using only its rotational period, period derivative, and surface temperature in the quiescent mode.
Two Modes of Partially Screened Gap
Andrzej Szary,George Melikidze,Janusz Gil
Physics , 2014, DOI: 10.1093/mnras/stu2622
Abstract: The analysis of X-ray observations suggest an ultrastrong ($B\gtrsim 10^{14} \,{\rm G}$) surface magnetic field at the polar cap of pulsars (Szary, 2013). On the other hand, the temperature of the polar caps is about a few millions Kelvin. Based on these two facts we use the Partially Screened Gap (PSG) model to describe the Inner Acceleration Region (IAR). The PSG model assumes that the temperature of the actual polar cap is equal to the so-called critical value, i.e. the temperature at which the outflow of thermal ions from the surface screens the gap completely. We have found that, depending on the conditions above the polar cap, the generation of high energetic photons in IAR can be caused either by Curvature Radiation (CR) or by Inverse Compton Scattering (ICS). Completely different properties of both processes result in two different scenarios of breaking the acceleration gap: the so-called PSG-off mode for the gap dominated by CR and the PSG-on mode for the gap dominated by ICS. The existence of two different mechanisms of gap breakdown naturally explains the mode-changing phenomenon. Different characteristics of plasma generated in the acceleration region for both modes also explain the pulse nulling phenomenon.
Observational consequences of the Partially Screened Gap
Andrzej Szary,George Melikidze,Janusz Gil
Physics , 2012,
Abstract: Observations of the thermal X-ray emission from old radio pulsars implicate that the size of hot spots is much smaller then the size of the polar cap that follows from the purely dipolar geometry of pulsar magnetic field. Plausible explanation of this phenomena is an assumption that the magnetic field at the stellar surface differs essentially from the purely dipolar field. Using the conservation of the magnetic flux through the area bounded by open magnetic field lines we can estimate the surface magnetic field as of the order of $10^{14}$G. Based on observations that the hot spot temperature is about a few million Kelvins the Partially Screened Gap (PSG) model was proposed which assumes that the temperature of the actual polar cap equals to the so called critical temperature. We discuss correlation between the temperature and corresponding area of the thermal X-ray emission for a number of pulsars. We have found that depending on the conditions in a polar cap region the gap breakdown can be caused either by the Curvature Radiation (CR) or by the Inverse Compton Scattering (ICS). When the gap is dominated by ICS the density of secondary plasma with Lorentz factors $10^{2}-10^{3}$ is at least an order of magnitude higher then in a CR scenario. We believe that two different gap breakdown scenarios can explain the mode-changing phenomenon and in particular the pulse nulling. Measurements of the characteristic spacing between sub-pulses ($P_{2}$) and the period at which a pattern of pulses crosses the pulse window ($P_{3}$) allowed us to determine more strict conditions for avalanche pair production in the PSG.
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