Hot Thermal Plasma Research Articles

Diagnostics of hot thermal plasma in flare-associated X-ray ejections

This is the first analysis of the soft X-ray spectra of flare-associated X-ray ejections. For this aim, the Yohkoh Bragg Crystal Spectrometer data recorded before two behind-the-limb flares were selected. These flares came into view from behind the solar limb but their occurrence was preceded by an X-ray ejection which expanded faster. In consequence, for several minutes the X-ray ejection was seen alone, without the presence of the brighter flare. Parameters of the plasma obtained from a fitting of synthetic spectra to observed spectra are presented and compared to images from the Yohkoh Soft X-ray Telescope. The presence of a minor fraction of the very hot (∼30 MK) thermal plasma in X-ray ejections is confirmed. High values of the non-thermal line broadening are caused by a large extension of X-ray ejections.

Energetic electrons in solar flares as viewed in X-rays

Hard X-ray observations provide the most direct diagnostic we have of the suprathermal electrons and the hottest thermal plasma present in solar flares. The Ramaty High Energy Solar Spectroscopic Imager (RHESSI) is obtaining the most comprehensive observations of individual solar flares ever available in hard X-rays. For the first time, high-resolution spectra are available for a large number of flares that accurately display the spectral shape and its evolution and, in many cases, allow us to identify the transition from the bremsstrahlung X-rays produced by suprathermal electrons to the bremsstrahlung at lower energies emitted by thermal plasma. Also, for the first time, images can be produced in arbitrary energy bands above 3–4 keV, and spectra of distinct imaged components can be obtained. I review what we have learned from RHESSI observations about flare suprathermal electron distributions and their evolution. Next, I present computations of the energy deposited by these suprathermal electrons in individual flares and compare this with the energy contained in the hot thermal plasma. I point out unsolved problems in deducing both suprathermal electron distributions and the energy content of the thermal plasma, and discuss possible solutions. Finally, I present evidence that electron acceleration is associated with magnetic reconnection in the corona.

Chandra X-ray Observations of Dwarf Starburst Galaxies

We obtained X-ray observations for a sample of eight nearby dwarf starburst galaxies from the Chandra X-ray Observatory. Five galaxies of our sample show extended (size: 1-10 kpc), diffuse X-ray emission which can be attributed to a hot thermal plasma. This phase of the interstellar medium purportedly drives the expansion of supergiant shells. A comparison of the derived gas parameters with theoretical models reveals that the hot gas in principle is capable to escape from the gravitational potential of the host galaxy. However, the outflows appear to be contained in those cases where an extended envelope or massive tidal features of neutral gas exist.

An XMM-Newton hard X-ray survey of ultraluminous infrared galaxies

XMM-Newton observations of 10 ultraluminous infrared galaxies (ULIRGs) from a 200-ks mini-survey programme are reported. The aim is to investigate in hard X-rays a complete ULIRG sample selected from the bright IRAS 60-μm catalogue. All sources are detected in X-rays, five of which for the first time. These observations confirm that ULIRGs are intrinsically faint X-ray sources, their observed X-ray luminosities being typically L 2 - 1 0 k e V ≤ 10 4 2 -10 4 3 erg s - 1 , whereas their bolometric (mostly infrared) luminosities are L b o l > 10 4 5 erg s - 1 . In all sources we find evidence for thermal emission from hot plasma with a rather constant temperature kT ≃ 0.7 keV, dominating the X-ray spectra below 1 keV, and probably associated with a nuclear or circumnuclear starburst. This thermal emission appears uncorrelated with the far-infrared luminosity, suggesting that, in addition to the ongoing rate of star formation, other parameters may also affect it. The soft X-ray emission appears to be extended on a scale of ∼30 kpc for Mrk 231 and IRAS 19254-7245, possible evidence of galactic superwinds. In these two sources, IRAS 20551-4250 and 23128-5919, we find evidence for the presence of hidden active galactic nuclei (AGNs), while a minor AGN contribution may be suspected also in IRAS 20100-4156. In particular, we have detected a strong (EW ∼ 2 keV) Fe K line at 6.4 keV in the spectrum of IRAS 19254-7245 and a weaker one in Mrk 231, suggestive of deeply buried AGNs. For the other sources, the X-ray luminosities and spectral shapes are consistent with hot thermal plasma and X-ray binary emissions of mainly starburst origin. We find that the 2-10 keV luminosities in these sources, most probably due to high-mass X-ray binaries, are correlated with L F I R : both luminosities are good indicators of the current global star formation rate in the Galaxy. The composite nature of ULIRGs is then confirmed, with hints for a predominance of the starburst over the AGN phenomenon in these objects even when observed in hard X-rays.

Dwarf Galaxies: The Interstellar‐Intergalactic Medium Connection

Starburst-driven superwinds in galaxies have the potential to transport interstellar material (ISM) to the intergalactic medium (IGM). The mechanism is expected to be a function of the gravitational potential of the host galaxy, low-mass galaxies being more likely to lose mass in an outflow. In order to investigate the possibility of dwarf galaxies shedding enriched, hot material into the IGM, we selected, in addition to data directly obtained by us, archival data on a sample of nearby dwarf starburst galaxies that were observed with the Chandra X-Ray Observatory (employing the ACIS-S3 CCD). The sample comprises eight objects: I Zw 18, VII Zw 403, IC 2574 (actually a nonstarburst galaxy but containing a bright starburst region), NGC 1569, NGC 3077, NGC 4449, NGC 5253, and He 2-10. Toward each of the targets we detected unresolved X-ray sources (at the 1 .1 resolution of Chandra), which are thought to be related to the galaxies. They are in general located in the vicinity of bright H ii regions or on the rims of supergiant shells. This, plus their spectral properties, points at high-mass stars being ultimately responsible. Diffuse X-ray emission, attributed to the emission from a hot thermal plasma, was detected in NGC 1569, NGC 3077, NGC 4449, NGC 5253, and He 2-10. The size of the diffuse component varies between 1 and 10 kpc. Averaged over the entire galaxy, we derive X-ray luminosities of the hot gas in the range of 10–10 ergs s , temperatures of ∼ K, 1 6 3 # 10 and densities of ∼0.02 cm (MeKaL models; is the 0.5 3 f f v v volume filling factor). The pressures were found to be P/k ≈ K cm . This is an order of magnitude higher than 5 0.5 3 10 fv typical pressures of the ISM in the Milky Way, hence the hot gas must be expanding. The values quoted critically depend on the plasma models used for the fits; a disconcerting result is that equally good “best” fits can be obtained that vary by up to an order of magnitude in their unabsorbed X-ray luminosities. One of the galaxies, NGC 3077, is studied in depth in this thesis. In this galaxy, the hot gas is found to be confined to expanding Ha superbubbles. As in the other galaxies with extended emission, the energy provided by the starburst is high enough, in principle, for the hot gas to escape from the gravitational potential of the respective host. However, additional work is needed to overcome an extended gaseous environment. We argue that in NGC 3077, at least some of the gas is lost toward the north but not toward the south. The situation is similar in NGC 4449, where the hot gas extends beyond the optical disk but seems to be confined by a large H i ring of tidal origin. In NGC 1569 and NGC 5253, the X-ray emission resembles a freely flowing wind. This picture is supported by steeper volume density profiles of the hot gas as compared to NGC 3077 and NGC 4449. Normalized, azimuthally averaged surface brightness profiles of the Ha and the diffuse X-ray emission are very similar, suggesting a common origin. A comparison of the hot-gas masses derived on the basis of the X-ray data with estimates of stellar mass loss reveals that, except for NGC 3077, additional material (of up to a factor of 100) must have become entrained in the expanding X-ray plasma (mass loading). If diffuse, hot gas exists in I Zw 18, VII Zw 403, or IC 2574 with similar properties as that in the other objects, the low metallicity of these galaxies can explain the fact that they remained below the detection threshold. However, alternative explanations such as larger than predicted internal absorption, substantially lower or higher temperatures of the plasma, or loss of the coronal gas through blowout cannot be excluded at present.

Understanding the Long‐Term Spectral Variability of Cygnus X‐1 with Burst and Transient Source Experiment and All‐Sky Monitor Observations

We present an analysis of all observations of Cygnus X-1 by the BATSE (20-300 keV) and by ASM (1.5-12 keV) until 2002 June, including 1200 days of simultaneous data. We find a number of correlations between fluxes and hardnesses in different energy bands. In the hard state, the variability can be explained by softening the overall spectrum with a pivot at 50 keV and another, independent variability pattern where the spectral shape does not change when the luminosity changes. In the soft state, the variability is caused by a variable hard tail of a constant shape superimposed on a constant soft component. These variability patterns are in agreement with the energy-dependent rms variability in the two states. We also study in detail recent soft states in 2000-02. The last of them has lasted so far for >200 days. Their spectra are harder in the 1.5-5 keV band but similar or in the 3-12 keV band than those of the 1996 soft state whereas the rms variability is stronger in all the ASM bands. On the other hand, the 1994 soft state transition observed by BATSE appears very similar to the 1996 one. We interpret the variability patterns by theoretical Comptonization models. In the hard state, the variability appears to be driven mostly by changing flux in seed photons Comptonized in a hot thermal plasma cloud with an approximately constant power supply. In the soft state, the variability is consistent with flares of hybrid, thermal/nonthermal, plasma with variable power above a stable cold disk. The spectral and timing differences between the 1996 and 2000-02 soft states are explained by a decrease of the color disk temperature. Also, based on broad-band pointed observations, we find the intrinsic bolometric luminosity increases by a factor of 3-4 from the hard state to the soft one.

The X-Ray Spectra of VY Sculptoris Stars Are Not Blackbodies

Using ASCA data, we find, contrary to other researchers using ROSAT data, that the X-ray spectra of the VY Sculptoris stars TT Arietis and KR Aurigae are poorly fitted by an absorbed blackbody model but are well fitted by an absorbed thermal plasma model. The different conclusions about the nature of the X-ray spectrum of KR Aur may be due to differences in the accretion rate since this star was in a high optical state during the ROSAT observation but in an intermediate optical state during the ASCA observation. TT Ari, on the other hand, was in a high optical state during both observations and so directly contradicts the hypothesis that the X-ray spectra of VY Scl stars in their high optical states are blackbodies. Instead, based on theoretical expectations and the ASCA, Chandra, and XMM spectra of other nonmagnetic cataclysmic variables, we believe that the X-ray spectra of VY Scl stars in their low and high optical states are due to hot thermal plasma in the boundary layer between the accretion disk and the surface of the white dwarf, and we appeal to the acquisition of Chandra and XMM grating spectra to test this prediction.

Sites of hot thermal plasma in solar flares

The time evolution of the emission measure derived from the Bragg Crystal Spectrometer (Fe xxv channel) and from the Soft X-ray Telescope images for 27 limb flares well-observed by Yohkoh has been compared. The ratio q of these two emission measures has been used as an estimation of relative contribution of hot thermal plasma. It has been confirmed that hot plasma is situated mainly inside the bright loop-top kernels, where it co-exists with cooler plasma. The maximal relative contribution q max of hot plasma in kernels is larger for lower-situated events, which suggests a dependence on the amount of released energy. A method checking how well the bright loop-top kernel represents the site of hot thermal plasma has been proposed.

A quasi-spherical inner accretion flow in Seyfert galaxies?

We study a phenomenological model for the continuum emission of Seyfert galaxies. In this quasi-spherical accretion scenario, the central X-ray source is constituted by a hot spherical plasma region surrounded by spherically distributed cold dense clouds. The cold material is radiatively coupled with the hot thermal plasma. Assuming energy balance, we compute the hard X-ray spectral slope Gamma and reflection amplitude R. This simple model enables to reproduce both the range of observed hard X-ray spectral slopes, and reflection amplitude R. It also predicts a correlation between R and Gamma which is very close to what is observed. Most of the observed spectral variations from source to source, would be due to differences in the cloud covering fraction. If some internal dissipation process is active in the cold clouds, darkening effects may provide a simple explanation for the observed distributions of reflection amplitudes, spectral slopes, and UV to X-ray flux ratios.

Charge conservation in electromagnetic PIC codes; spectral comparison of Boris/DADI and Langdon-Marder methods

Non-charge conserving current collection algorithms for electromagnetic PIC plasma simulations may cause errors in Gauss's law. These errors arise from violations of the charge continuity equation, ∇ · J = −ϵπ/ϵt, which is turn cause errors in the irrotational part of E. Two techniques for reducing these errors are examined and compared: a modified Marder correction which corrects electric fields locally and primarily affects short wavelengths, and a Boris divergence correction, which solves Poisson's equation to correct the electric fields so that Gauss's law is enforced globally. The effect of each method on the spectrum of the error is examined. Computational efficiency and accuracy of the two techniques are compared: neither method is clearly superior. Cases examined include corrections in electromagnetic relativistic beam simulations, and a hot thermal plasma. In addition, the spectral comparison provides insight into the behavior of the schemes applied.

Evidence for a Pulsar Jet Producing a Hot Nebula in the Supernova Remnant MSH 15—52

We have discovered direct evidence for a pulsar jet from the young X-ray and radio pulsar PSR 1509–58 in the supernova remnant MSH 15–52 with the X-ray astronomy satellite ASCA. With its high-energy resolution combined with its imaging capability over a wide energy band, ASCA has studied the two morphologically and spectroscopically different components in this supernova remnant: a non-thermal nebula powered by the pulsar with a jet-like structure, and a hot thermal plasma cloud located at the end of the “jet”. We propose that the jet is a stream of relativistic electrons generated by the pulsar, and that the thermal nebula is created by the collision of the jet with interstellar matter. This scenario can explain the peculiar X-ray morphology and the energy budget of MSH 15–52 consistently.

Anisotropic Comptonization in thermal plasmas - Spectral distribution in plane-parallel geometry

view Abstract Citations (97) References (28) Co-Reads Similar Papers Volume Content Graphics Metrics Export Citation NASA/ADS Anisotropic Comptonization in Thermal Plasmas: Spectral Distribution in Plane-Parallel Geometry Haardt, Francesco Abstract We present a semi-analytical formulation of the problem of inverse Compton scattering of low-frequency radiation in a hot thermal plasma. The scattering medium is assumed to have a plan-parallel geometry, and an input radiation field is localized on one side of the slab. The angular and energy distributions of the emitted radiation are computed taking into account the effects due to the anisotropy of the input photons. We show how the Comptonized spectrum depends on three parameters, namely the optical depth of the medium, the temperature of thermal electrons, and the viewing angle. The spectral shape is approximately, but not exactly, a broken power law. Our method allows to compute angle-dependent Compton spectra for a broad range of input parameters with a modest computational effort. Publication: The Astrophysical Journal Pub Date: August 1993 DOI: 10.1086/173036 Bibcode: 1993ApJ...413..680H Keywords: Anisotropy; Compton Effect; Electron Scattering; Photons; Thermal Plasmas; Electron Distribution; Iteration; Probability Density Functions; Plasma Physics; RADIATION MECHANISMS: MISCELLANEOUS; RADIATIVE TRANSFER full text sources ADS |

Impact line linear polarization as a diagnostic of 100 keV proton acceleration in solar flares

view Abstract Citations (84) References (24) Co-Reads Similar Papers Volume Content Graphics Metrics Export Citation NASA/ADS Impact Line Linear Polarization as a Diagnostic of 100 keV Proton Acceleration in Solar Flares Henoux, J. C. ; Chambe, G. ; Smith, D. ; Tamres, D. ; Feautrier, N. ; Rovira, M. ; Sahal-Brechot, S. Abstract The use of impact linear polarization of chromospheric lines as a diagnostic of 100 keV protons is proposed. Observations of hard X-ray emission are examined, noting the possibility that 100 keV proton beams bombarding the atmosphere could create a hot thermal plasma at the origin of X-ray emission. The application of impact linear line polarization as a diagnostic of the existence of energetic particles with anisotropic velocity distribution functions is described. The mechanisms leading to an anisotropic proton distribution in the solar chromosphere are discussed and the required initial energy and energy flux for accelerated protons in the corona are derived. It is suggested that it is possible to infer the original proton anisotropy in the corona and the effect of this anisotropy on the proton energy and proton energy flux required to reach the H-alpha-forming layers. Publication: The Astrophysical Journal Supplement Series Pub Date: June 1990 DOI: 10.1086/191466 Bibcode: 1990ApJS...73..303H Keywords: Linear Polarization; Particle Acceleration; Solar Flares; Solar Protons; Chromosphere; Emission Spectra; Proton Beams; Solar Atmosphere; Solar Spectra; Solar X-Rays; Solar Physics; PARTICLE ACCELERATION; POLARIZATION; SUN: FLARES; SUN: PARTICLE EMISSION; SUN: X-RAYS full text sources ADS |

The influence of centrifugal forces on the B field structure of an axially symmetric equilibrium magnetosphere

We investigate a stationary model of a rotating, axially symmetric “pole‐on” magnetosphere in MHD force balance. In this model both the planet's rotational and dipole axes are aligned with the magnetotail axis, which is the axis of symmetry in a cylindrical (r, ϕ, z) coordinate system. For mathematical convenience the magnetosphere is confined on the nightside by a cylindrical magnetopause with constant radius. On the sunward side, the magnetosphere is closed by an appropriate image dipole. Inside the magnetospheric cavity we assume isotropic thermal plasma pressure. We assume further that, in general, planetary rotation leads to differentially rotating magnetotail field lines causing field‐aligned Birkeland currents and a corresponding toroidal magnetic Bϕ component which leads to twisted magnetotail field lines. We calculate the deformation of magnetotail field lines under the influence of both thermal plasma pressure and centrifugal forces. We present “linear” (analytic) solutions to the Grad‐Shafranov equation which include the centrifugal force term. In the linear model, two free physical parameters, k and ω, measure the plasma thermal pressure and the ratio between plasma rotational and thermal energy densities, respectively. Low ω and high k values indicate the plasma‐dominated case. Conversely, low k and high ω values indicate the rotation‐dominated case. One limiting case, k = ω = 0, generates a simple vacuum magnetic field of a dipole confined within the magnetospheric cavity. The nonrotational magnetosphere with hot thermal plasma leads to a field configuration without a toroidal Bϕ component and without field‐aligned Birkeland currents. The other extreme, namely, a rapidly rotating magnetosphere with cold plasma, leads to a configuration in which the plasma must be confined within a thin disk in a plane where the radial magnetic field component Br vanishes locally. Utmost stretched magnetotail configurations can be achieved by increasing either the plasma thermal pressure or the rotation frequency of the magnetosphere, or both. In the rotation‐dominated case we found the plasma sheet thinner and located closer to the magnetopause than in the purely plasma‐dominated case. This implies that hypothetical polar aurorae, under the influence of magnetospheric rotation, appear at higher magnetic latitudes on both the dayside and the nightside. This also implies that the size of the polar oval shrinks under the influence of magnetospheric rotation. A “pole‐on” magnetosphere can be expected at Uranus in the year 2014 twice during a Uranian day.

Hard X-ray imaging observations of solar hot thermal flares with the HINOTORI spacecraft

Two solar hard X-ray bursts of a new type (hot thermal flare) were observed with hard X-ray imaging telescopes and other instruments on Japanese spacecraft Hinotori. The flares have no clear impulsive phase below 40 keV and emit intense hard X-rays (10--50 keV) with extremely steep spectra from a small region with size (FWHM) of 10''--20''. This source contains a hot thermal plasma of (3--3.5) x 10/sup 7/ K with an emission measure of the order of 10/sup 49/ cm/sup -3/. One of the flares occurred just on the limb, and the centroid of the hard X-ray (14-38 keV) source was located at (6 +- 3) x 10/sup 3/ km above the photosphere. It is concluded that the energy continuously released goes into heating rather than acceleration almost throughout the flare. Typical impulsive flares may usually have a similar nature in the later phase (gradual phase) of the flare evolution. The number density of the hard X-ray emitting region was higher than (6-10) x 10/sup 10/ cm/sup -3/ even in the initial phase of the flare, probably due to its low altitude. We infer that this high density made acceleration difficult, and therefore unusually intense heating occurred from the startmore » of the flare.« less

He D3 as a diagnostic for the hard and soft X-rays from solar flares

The time comparison of He D3 and X-ray emission has been studied in a number of medium-sized flares. In most cases there is a good agreement between the time histories of the He D3 emission and the high-temperature (about 2 keV) thermal source. The most intense He D3 emission comes from two small regions on either side of the neutral line, which are identified with the footpoints of magnetic structures in which a hot (2.3 x 10 to the 7th K) thermal plasma is formed. The impulsive X-ray event is marked by the transient brightening of a number of (usually weaker) He D3 sources. The two types of sources are well displaced from each other, which is an indication that they are produced in two different volumes. In some cases a long-lived third He D3 source is seen.

Interpretation of the soft X-ray spectra from Hinotori

We present analyses of the soft X-ray iron line spectra of flares obtained from the Bragg Spectrometer on Hinotori. We first present a case of strong Kα emission at the impulsive phase of the hard X-ray burst, and assess net Kα emission due to the electron impact by eliminating the fluorescence contribution. Second we discuss on the differences in the electron temperatures and emission measures derived respectively from FeXXVI and FeXXV spectra. A pilot two-temperatures model which can explain the two spectra is presented. Finally, we compare the temporal relations between the soft X-ray and hard X-ray intensities and show two extreme classes of flares, one characterized by the efficient formation of a hot thermal plasma above 30 million degree, and the other characterized by the spiky hard X-ray component. Energetical relation of the thermal plasma to the electron beam is discussed for the two classes.

Thermal evolution of flare plasma

The evolution of hot thermal plasma in solar flares is analyzed by a single-temperature model applied to continuum emission in the 5 keV < E < 13 keV spectral range. The general trend that the thermal plasma observed in soft X-rays is heated by the non-thermal electrons that emit as the hard X-ray bursts is confirmed by the observation of an electron temperature increase at the time interval of hard X-ray spikes and a quantitative comparison between thermal energy content and hard X-ray energy input. Non-thermal electrons of 10 keV < E < 30 keV energy may play an important role in pre- and post-burst phases.

Emission mechanism and source distances of γ-ray bursts

The reported continuum spectra (∼20 keV–2 MeV) of most γ-ray bursts resemble a simple exponential1–4. Hence, the conventional view is that they are the optically thin free–free (bremstralung) emission of a hot thermal plasma (kT ≳ 100 keV with the exception of a few soft events, notably the 5 March 1979 event). I show here that: (1) independent of the source distance, there is an inherent difficulty with the free–free interpretation if the sources are indeed neutron stars with magnetic field B ≳ 1012 G, because the synchrotron emissivity of these hot thermal electrons would greatly exceed then free–free emissivity for any reasonable electron density consistent with τes ≪ 1 required by observations; (2) the spectral data can be fitted equally well, if not better, by optically thin thermal synchrotron spectra of mildly relativistic (kT ∼ mc2) electrons; (3) the absence of observable low-energy turnover due to synchrotron self-absorption (or high energy Compton distortion) puts interesting upper limits to the source of luminosity and distance. Most sources are noncosmological (<10 kpc–1 Mpc) but not necessarily as nearby as some authors have suggested using the free–free spectral interpretation (see, for example, ref. 2).

Filter method and silicon detectors to measure the temperature of a hot dense thermal deuterium plasma from its quantum bremsstrahlung

The filter method, used to measure the temperature of a hot (T&amp;gt; 1 keV) deuterium plasma through its bremsstrahlung emission, is studied taking into account two new features: (i) the bremsstrahlung emission (accounted for, up until now, by its classical approximation) is described by its quantum expression, (ii) real solid-state silicon detectors are considered, instead of ideal ones. Deductions are made concerning the best choice of the detector and the corresponding adequate filter for different temperature ranges; the limits of the temperature ranges are established considering the minimum number of points necessary to identify the shape of the spectrum curve, as well as the loss of efficiency of the detectors at high energies. An upper bound is set to the measurable temperature. Neutron radiation damages to the Si detectors, at current and foreseen levels, are considered and shown to impose no serious limitation to the practical applicability of the method.