Adiabatic Losses Research Articles

Evolution of and High‐Energy Emission from GHz‐Peaked Spectrum Sources

Here we discuss evolution and broad-band emission of compact (< kpc) lobes in young radio sources. We propose a simple dynamical description for these objects, consisting of a relativistic jet propagating into a uniform gaseous medium in the central parts of an elliptical host. In the framework of the proposed model, we follow the evolution of ultrarelativistic electrons injected from a terminal hotspot of a jet to expanding lobes, taking into account their adiabatic energy losses as well as radiative cooling. This allows us to discuss the broad-band lobe emission of young radio sources. In particular, we argue that the observed spectral turnover in the radio synchrotron spectra of these objects cannot originate from the synchrotron self-absorption process but is most likely due to free-free absorption effects connected with neutral clouds of interstellar medium engulfed by the expanding lobes and photoionized by active centers. We also find a relatively strong and complex high-energy emission component produced by inverse-Compton up-scattering of various surrounding photon fields by the lobes electrons. We argue that such high energy radiation is strong enough to account for several observed properties of GHz-peaked-spectrum (GPS) radio galaxies at UV and X-ray frequencies. In addition, this emission is expected more » to extend up to GeV (or possibly even TeV) photon energies and can thus be probed by several modern {gamma}-ray instruments. In particular, we suggest that GPS radio galaxies should constitute a relatively numerous class of extragalactic sources detected by GLAST. « less

Supernova SN2006gy as a first ever Quark Nova?

The most luminous Supernova SN2006gy (more than a 100 times brighter than a typical supernova) has been a challenge to explain by standard models. For example, pair instability supernovae which are luminous enough seem to have too slow a rise, and core collapse supernovae do not seem to be luminous enough. We present an alternative scenario involving the quark-nova phenomenon (an explosive transition of the newly born neutron star to a quark star) in which a second explosion (delayed) occurs inside the ejecta of a normal supernova. The reheated supernova ejecta can radiate at higher levels for longer periods of time primarily due to reduced adiabatic expansion losses, unlike the standard supernova case. We find an encouraging match between the resulting lightcurve and that observed in the case of SN2006gy suggesting that we might have at hand the first ever signature of a quark-nova. Successful application of our model to SN2005gj and SN2005ap is also presented.

Modelling interaction of relativistic and non-relativistic winds in binary system PSR B1259−63/SS2883 – I. Hydrodynamical limit

In this paper, we present a detailed hydrodynamical study of the properties of the flow produced by the collision of a pulsar wind with the surrounding in a binary system. This work is the first attempt to simulate interaction of the ultrarelativistic flow (pulsar wind) with the non-relativistic stellar wind. Obtained results show that the wind collision could result in the formation of an 'unclosed' (at spatial scales comparable to the binary system size) pulsar wind termination shock even when the stellar wind ram pressure exceeds significantly the pulsar wind kinetic pressure. Moreover, the post-shock flow propagates in a rather narrow region, with very high bulk Lorentz factor (y ∼ 100). This flow acceleration is related to adiabatic losses which are purely hydrodynamical effects. Interestingly, in this particular case, no magnetic field is required for formation of the ultrarelativistic bulk outflow. The obtained results provide a new interpretation for the orbital variability of radio, X-ray and gamma-ray signals detected from binary pulsar system PSR B1259-63/SS2883.

Non-thermal emission from relativistic MHD simulations of pulsar wind nebulae: from synchrotron to inverse Compton

Aims. The goal of this paper is twofold. In the first place we complet e the set of diagnostic tools for synchrotron emitting sourc es presented by Del Zanna et al. (Astron. Astrophys. 453, 621, 2006 ) with the computation of inverse Compton radiation from the same relativistic particles. Moreover we investigate, for the fi rst time, the gamma-ray emission properties of Pulsar Wind Nebulae in the light of the axisymmetric jet-torus scenario. Methods. The proposed method consists in evolving the relativistic MHD equations and the maximum energy of the emitting particles including adiabatic and synchrotron losses along streamlines. The particle energy distribution function is split in t wo components: one corresponding to the radio emitting electrons interpreted as a relic population born at the outburst of the supernova and the other associated with the wind population continuously accelerated at the termination shock and emitting up to the gamma-ray band. The inverse Compton emissivity is calculated using the general Klein-Nishina differential cross-section and three different photon targets for the relativistic particles are considered: the nebular synchrotron photons, photons associated with the far-infrared thermal excess and the cosmic microwave background. Results. When the method is applied to the simulations that better reproduce the optical and X-ray morphology of the Crab Nebula, the overall synchrotron spectrum can only be fitted assuming an excess of injected particles and a steeper power law (E −2.7 ) with respect to previous models. The resulting TeV emission has then the correct shape but is in excess of the data. This is rela ted to the magnetic field structure in the nebula as obtained by the simu lations, in particular the field is strongly compressed near the termination shock but with a lower than expected volume average. The jet-torus structure is found to be clearly visible in high-resolution gammaray synthetic maps too. We also present a preliminary exploration of time variability in the X and gamma-ray bands. We find variations with time-scales of about 2 years in both bands. The variability observed originates from the strongly time-dependent MHD motions inside the nebula.

Adiabatic quenches through an extended quantum critical region

By gradually changing the degree of the anisotropy in an $XXZ$ chain, we study the defect formation in a quantum system that crosses an extended critical region. We discuss two qualitatively different cases of quenches, from the antiferromagnetic to the ferromagnetic phase and from the critical to the antiferromagnetic phase. By means of time-dependent density matrix renormalization group simulations, we calculate the residual energy at the end of the quench as a characteristic quantity gauging the loss of adiabaticity. We find the dynamical scalings of the residual energy for both types of quenches, and compare them to the predictions of the Kibble-Zurek and Landau-Zener theories.

Design and construction of a Stirling engine prototype

In this work an external combustion engine is presented, which was designed through principles of energetic similarity and scaling, combined with adiabatic simulation, pressure loss and heat exchange characteristics analysis. These type of engines have the great advantage of having the heat source applied from outside, therefore resulting in very versatile machines which can be utilized with hydrogen, concentrated solar energy, biomass or fossil fuels. Details of the construction carried out mostly with conventional machine parts produced in Argentina are given. Finally, the results of the preliminary tests with the constructed prototype are shown.

Shell-shocked Diffusion Model for the Light Curve of SN 2006gy

We explore a simple model for the high luminosity of SN 2006gy involving photon diffusion of shock-deposited thermal energy. The distinguishing property of the model is that the large “stellar” radius of ∼160 AU required to prevent adiabatic losses is not the true stellar radius, but rather, it is the radius of an opaque, unbound circumstellar envelope, created when ∼10 M, was ejected in the decade before the supernova in an eruption analogous to that of h Carinae. The supernova light is produced primarily by diffusion of thermal energy following the passage of the blast wave through this shell. This model differs from traditional models of supernova debris interacting with an external circumstellar medium (CSM) in that here the shell is optically thick and the escape of radiation is delayed. We show that any model attempting to account for SN 2006gy’s huge luminosity with radiation emitted by ongoing CSM interaction fails for the following basic reason: the CSM density required to achieve the observed luminosity makes the same circumstellar envelope opaque ( ), forcing a thermal t 300 diffusion solution. In our model, the weaker CSM interaction giving rise to SN 2006gy’s characteristic Type IIn spectrum and soft X-rays is not linked to the power source of the visual continuum; instead, it arises after the blast wave breaks free from the opaque shell into the surrounding wind. While a simple diffusion model can explain the gross properties of the early light curve of SN 2006gy, it predicts that the light curve must plummet rapidly at late times, unless an additional power source is present. Subject headings: circumstellar matter — stars: evolution — supernovae: individual (SN 2006gy)

Hybrid cross-linkable polymer/sol-gel waveguide modulators with 0.65V half wave voltage at 1550nm

The authors report on a hybrid cross-linked electro-optic (EO) polymer/sol-gel Mach-Zehnder waveguide modulator with a half wave voltage (Vπ) of 0.65V at 1550nm. The low Vπ was achieved by a design that (1) combines both physical vertical tapers in the sol-gel core and photobleached index tapers in the EO polymer and (2) reduces the thickness of the device to 8μm. These combined physical and index tapers result in improved optical mode confinement in the EO polymer with low adiabatic optical transition loss. The reduced thickness results in a larger field across the EO polymer for the same voltage, enabling a lower Vπ.

AChandraStudy of the Lobe/Interstellar Medium Interactions around the Inner Radio Lobes of Centaurus A: Constraints on the Temperature Structure and Transport Processes

We present results from deeper Chandra observations of the southwest radio lobe of Centaurus A, first described by Kraft and coworkers. We find that the sharp X-ray surface brightness discontinuity extends around ~75% of the periphery of the radio lobe and detect significant temperature jumps in the brightest regions of this discontinuity nearest to the nucleus. This demonstrates that this discontinuity is indeed a strong shock that is the result of an overpressure that has built up in the entire lobe over time. In addition, we demonstrate that if the mean free path for ions to transfer energy and momentum to the electrons behind the shock is as large as the Spitzer value, the electron and proton temperatures will not have equilibrated along the southwest boundary of the radio lobe where the shock is strongest. Thus, the proton temperature of the shocked gas could be considerably larger than the observed electron temperature, and the total energy of the outburst correspondingly larger as well. We investigate this using a simple one-dimensional shock model for a two-fluid (proton/electron) plasma. We find that for the thermodynamic parameters of the Cen A shock the electron temperature rises rapidly from ~0.29 keV (the temperature of the ambient ISM) to ~3.5 keV, at which point heating from the protons is balanced by adiabatic losses. The proton and electron temperatures do not equilibrate in a timescale less than the age of the lobe. We note that the measured electron temperature of similar features in other nearby powerful radio galaxies in poor environments may considerably underestimate the strength and velocity of the shock.

TeV light curve of PSR B1259-63/SS2883

The inverse Compton (IC) scattering of ultrarelativistic electrons accelerated at the pulsar wind termination shock is generally believed to be responsible for TeV gamma-ray signal recently reported from the binary system PSR B1259-63/SS2883. While this process can explain the energy spectrum of the observed TeV emission, the gamma-ray fluxes detected by the Array of Imaging Atmospheric Cherenkov Telescopes (HESS) at different epochs do not agree with the published theoretical predictions of the TeV light curve. The main objective of this paper is to show that the HESS results can be explained, under certain reasonable assumptions concerning the cooling of relativistic electrons, by IC scenarios of gamma-ray production in PSR B1259-63. In this paper we study evolution of the energy spectra of relativistic electrons under different assumptions about the acceleration and energy-loss rates of electrons, and the impact of these processes on the light curve of IC gamma-rays. We demonstrate that the observed TeV light curve can be explained (i) by adiabatic losses which dominate over the entire trajectory of the pulsar with a significant increase towards the periastron or (ii) by the 'early' (sub-TeV) cut-offs in the energy spectra of electrons due to the enhanced rate of Compton losses close to the periastron. The first four data points obtained just after periastron comprise an exception - possibly due to interaction with the Be star disc, which introduces additional physics not included in the presented model. The calculated spectral and temporal characteristics of the TeV radiation provide conclusive tests to distinguish between these two working hypotheses. The Compton deceleration of the electron-positron pulsar wind contributes to the decrease of the non-thermal power released in the accelerated electrons after the wind termination, and thus to the reduction of the IC and synchrotron components of radiation close to the periastron. Although this effect alone cannot explain the observed TeV and X-ray light curves, the Comptonization of the cold ultrarelativistic wind leads to the formation of gamma-radiation with a specific line-type energy spectrum. While the HESS data already constrain the Lorentz factor of the wind, Γ ≤ 10 6 (for the most likely orbit inclination angle i = 35°, and assuming an isotropic pulsar wind), future observations of this object with GLAST should allow a deep probe of the wind Lorentz factor in the range between 10 4 and 10 6 .

Relativistic proton production at the Sun in the 20 January 2005 solar event

Based on the concept of multiple acceleration of solar energetic particles (SEP) we analyzed the super-event of 20 January 2005 by the data of ground level, balloon and spacecraft observations. The main characteristics of relativistic solar protons (energy spectra, anisotropy directions and pitch-angle distributions) are derived and their dynamics during the event is studied. It is shown that the flux of relativistic solar protons may consist of two distinct components, the so-called prompt and delayed ones. Within a two-source model of particle generation, one of which is associated with an expanding magnetic loop, we solved the transport equation in energy phase space, including adiabatic losses simultaneously with the stochastic acceleration process, and calculate the expected spectra of the delayed component at the source. The confrontation of experimental spectra with theoretical ones shows that the delayed component may be correctly described by stochastic acceleration, but not the prompt component. The required acceleration efficiencies turned out to be rather high, so that, for this particular event, adiabatic cooling is practically negligible. Our results provide a new support to the existence of two populations of relativistic solar protons in some SEP events.

A dip in the UHECR spectrum and the transition from galactic to extragalactic cosmic rays

The dip is a feature in the diffuse spectrum of ultra-high energy (UHE) protons in the energy range 1 × 10 18–4 × 10 19 eV, which is caused by electron–positron pair production on the cosmic microwave background (CMB) radiation. For a power-law generation spectrum E −2.7, the calculated position and shape of the dip is confirmed with high accuracy by the spectra observed by the Akeno-AGASA, HiRes, Yakutsk and Fly’s Eye detectors. When the particle energies, measured in these detectors, are calibrated by the dip, their fluxes agree with a remarkable accuracy. The predicted shape of the dip is quite robust: it is modified very weakly when the discreteness and inhomogeneities in the source distribution are taken into account, and for different regimes of propagation (from rectilinear to diffusive). The cosmological evolution of the sources, with parameters inspired by observations of Active Galactic Nuclei (AGN), also results in the same shape of the dip. The dip is modified strongly when the fraction of nuclei heavier than protons is high at injection, which imposes some restrictions on the mechanisms of acceleration operating in UHECR sources. The existence of the dip, confirmed by observations, implies that the transition from galactic to extragalactic cosmic rays occurs at E ≲ 1 × 10 18 eV. We show that at energies lower than a characteristic value E cr ≈ 1 × 10 18 eV, determined by the equality between the rate of energy losses due to pair production and adiabatic losses, the spectrum of extragalactic cosmic rays flattens in all cases of interest, and it provides a natural transition to a steeper galactic cosmic ray spectrum. This transition occurs at some energy below E cr, corresponding to the position of the so-called second knee. We discuss extensively the constraints on this model imposed by current knowledge of acceleration processes and sources of UHECR and compare it with the traditional model of transition at the ankle.

On transiton from galactic to extragalactic cosmic rays

The dip is a feature in the diffuse spectrum of UHE protons in energy range 1 × 1018 − 4 × 1019 eV, which is caused by electron-positron pair production on CMB photons. Calculated for power-law generation spectrum with index γg = 2.7, the shape of the dip is confirmed with high accuracy by data of Akeno - AGASA, HiRes, Yakutsk and Fly's Eye detectors. The predicted shape of the dip is robust: it is valid for the rectilinear and diffusive propagation, for different discretenesses in the source distribution, for local source overdensity and deficit, for source inhomogeneities on scale∼l100 Mpc etc. Below the characteristic energy Ec ≈ 1 × 1018 eV the spectrum of the dip flattens for both diffusive and rectilinear propagation, and more steep galactic spectrum becomes dominant at E < Ec. The energy of transition Etr < Ec approximately coincides with the position of the second knee E2kn observed in the cosmic ray spectrum. The critical energy Ec is determined by the energy Eeq = 2.3 × 1018 eV, where adiabatic and pair-production energy losses are equal. Thus, position of the second knee is explained by proton energy losses on CMB photons. The transition from galactic to extragalactic cosmic rays is quantitatively described by the AGN model for UHECR.

Effect of adiabatic cooling on the fitted parallel mean free path of solar energetic particles

The focused transport equation without adiabatic energy loss is widely used to model solar energetic particles' (SEP) interplanetary propagation by fitting spacecraft data. We incorporate the adiabatic energy loss effect, provided by the divergence of the solar wind flows, into the focused transport equation. The equation is then solved numerically using a time‐backward stochastic integration method. We show the comparison between solutions of focused transport equations with and without energy loss. We found the effect of adiabatic cooling is significant on the time profile of the intensity of SEPs. It is also shown that without energy loss, for gradual events, we can only fit the initial phase of SEP events. However, with energy loss, we can fit the entire (initial and decaying) phases. In addition, the values of the mean free path obtained by fitting the SEP events with energy loss is always smaller than that without. The results suggest that including adiabatic cooling effect is another way to partially fix the solar energetic particle mean free paths' “too small” problem discussed by Bieber et al. (1994), i.e., the mean free paths obtained by fitting transport equation to observation data are much larger than the quasi‐linear theory results.

Simulated synchrotron emission from pulsar wind nebulae

Aims. A complete set of diagnostic tools aimed at producing synthetic synchrotron emissivity, polarization, and spectral index maps from relativistic MHD simulations is presented. As a first application we consider here the case of the emission from Pulsar Wind Nebulae (PWNe). Methods. The proposed method is based on the addition, on top of the basic set of MHD equations, of an extra equation describing the evolution of the maximum energy of the emitting particles. This equation takes into account adiabatic and synchrotron losses along streamlines for the distribution of emitting particles and its formulation is such that it is easily implemented in any numerical scheme for relativistic MHD. Results. Application to the axisymmetric simulations of PWNe, analogous to those described by Del Zanna et al. (2004), allows direct comparison between the numerical results and observations of the inner structure of the Crab Nebula, and similar objects, in the optical and X-ray bands. We are able to match most of the observed features typical of PWNe, like the equatorial torus and the polar jets, with velocities in the correct range, as well as finer emission details, like arcs, rings and the bright knot, that turn out to arise mainly from Doppler boosting effects. Spectral properties appear to be well reproduced too: detailed spectral index maps are produced for the first time and show softening towards the PWN outer borders, whereas spectral breaks appear in integrated spectra. The emission details are found to strongly depend on both the average wind magnetization, here σeff ≈ 0.02, and on the magnetic field shape. Conclusions. Our method, in spite of its simplicity, provides a realistic modeling of synchrotron emission properties, and twodimensional axisymmetric relativistic MHD simulations appear to be well suited to explain the main observational features of PWNe.

Cosmic ray energy changes in the heliosphere: Effects of the termination shock and heliosheath

Adiabatic energy losses form a well‐understood part of cosmic ray modulation in the heliosphere. However, shock acceleration at the solar wind termination shock and the modulation in the heliosheath beyond this shock alter the net cosmic ray energy change from that in standard no–shock modulation models. This paper compares cosmic ray energy changes in several versions of the modulation process, from the simplest Force‐Field model to one with a shock and heliosheath included. Implications for observations and their interpretation are noted. In particular, the shock acceleration mechanism seems to provide a sensitive probe of interstellar spectra at low energies (≤100 MeV/n) that was not previously appreciated. The consequence of this effect on the low‐energy ratio of secondary to primary cosmic rays will be investigated in a subsequent paper.

Spectral energy distribution of the γ-ray microquasar LS 5039

The microquasar LS 5039 has recently been detected as a source of very high energy (VHE) γ -rays. This detection, that confirms the previously proposed association of LS 5039 with the EGRET source 3EG J1824-1514, makes of LS 5039 a special system with observational data covering nearly all the electromagnetic spectrum. In order to reproduce the observed spectrum of LS 5039, from radio to VHE γ -rays, we have applied a cold matter dominated jet model that takes into account accretion variability, the jet magnetic field, particle acceleration, adiabatic and radiative losses, microscopic energy conservation in the jet, and pair creation and absorption due to the external photon fields, as well as the emission from the first generation of secondaries. The radiative processes taken into account are synchrotron, relativistic Bremsstrahlung and inverse Compton (IC). The model is based on a scenario that has been characterized with recent observational results, concerning the orbital parameters, the orbital variability at X-rays and the nature of the compact object. The computed spectral energy distribution (SED) shows a good agreement with the available observational data.

Mean-field dynamics of a Bose-Einstein condensate in a time-dependent triple-well trap: Nonlinear eigenstates, Landau-Zener models, and stimulated Raman adiabatic passage

We investigate the dynamics of a Bose-Einstein condensate in a triple-well trap in a three-level approximation. The interatomic interactions are taken into account in a mean-field approximation (Gross-Pitaevskii equation), leading to a nonlinear three-level model. Additional eigenstates emerge due to the nonlinearity, depending on the system parameters. Adiabaticity breaks down if such a nonlinear eigenstate disappears when the parameters are varied. The dynamical implications of this loss of adiabaticity are analyzed for two important special cases: A three-level Landau-Zener model and the stimulated Raman adiabatic passage (STIRAP) scheme. We discuss the emergence of looped levels for an equal-slope Landau-Zener model. The Zener tunneling probability does not tend to zero in the adiabatic limit and shows pronounced oscillations as a function of the velocity of the parameter variation. Furthermore we generalize the STIRAP scheme for adiabatic coherent population transfer between atomic states to the nonlinear case. It is shown that STIRAP breaks down if the nonlinearity exceeds the detuning.

Performance analysis and parametric optimum criteria of an irreversible Atkinson heat-engine

Multi-irreversibilities, mainly resulting from the adiabatic processes, finite-time processes and heat loss through the cylinder wall, are considered in the cycle model of an Atkinson heat engine. The power output and efficiency of the cycle are derived by introducing the pressure ratio and the compression and expansion efficiencies. The performance characteristic curves of the cycle are presented. The bounds of the power output and efficiency are determined. The optimum criteria of some important parameters, such as the power output, efficiency and pressure ratio are given. The influences of the various design parameters on the performance of the cycle are analyzed in detail. The results obtained may provide a theoretical basis for both the optimal design and operation of real Atkinson heat engines.

Cool Customers in the Stellar Graveyard. III. Limits to Substellar Objects around nearby White Dwarfs using the Canada-France-Hawaii Telescope

Results from a ground-based high-contrast imaging survey of 13 nearby white dwarfs for substellar objects are presented. We place strict upper limits on the type of substellar objects present, ruling out the presence of anything larger than ~14MJ for eight of the white dwarfs at separations >19 AU and corresponding to primordial separations of ~3–6 AU assuming adiabatic mass loss without tidal interactions. With these results we place the first upper limit on the number of intermediate-mass stars with brown dwarfs at separations >13 AU. We combine these results with previous work to place upper limits on the number of massive Jovian (>10MJ) planets in orbit around white dwarfs whose progenitors spanned a mass range of 1–7 M⊙.