A survey of radio jets with Chandra and HST

Relativistic jets are a common property of radio-loud Active Galactic Nuclei (AGN). Understanding jet physical properties is an essential precursor to understanding the mechanisms of energy transport, and ultimately, how energy is extracted from the central black hole. In this paper, I highlight recent developments from Chandra and HST observations of kpc-scale jets in AGN, with particular emphasis on our survey of 17 radio jets in a sample of FRII radio galaxies. These observations show that (1) X-ray and optical emission is common from kpc-scale jets, (2) a large fraction of the bolometric luminosity is emitted at X-rays, and (3) in most sources, a candidate emission process for the X-rays is inverse Compton scattering of the Cosmic Microwave Background off the relativistic electrons in the jet. If the latter scenario holds, the implication is that jets are still relativistic on kpc scales.     

The nature of nonthermal X-ray filaments near the galactic center

Recent Chandra and XMM-Newton observations reported evidence of two X-ray filaments G359.88−0.08 (SgrA-E) and G359.54+0.18 (the ripple filament) near the Galactic center. The X-ray emission from these filaments has a nonthermal spectrum and coincides with synchrotron emitting radio sources. Here, we report the detection of a new X-ray feature coincident with a radio filament G359.90−0.06 (SgrA-F) and show more detailed VLA, Chandra and BIMA observations of the radio and X-ray filaments. In particular, we show that radio emission from the nonthermal filaments G359.90−0.06 (SgrA-F) and G359.54+0.18 (the ripple) has a steep spectrum whereas G359.88−0.08 (SgrA-E) has a flat spectrum. The X-ray emission from both these sources could be due to synchrotron radiation. However, given that the 20 km s⁻¹ molecular cloud, with its intense 1.2 mm dust emission, lies in the vicinity of SgrA-F, it is possible that the X-rays could be produced by inverse Compton scattering of far-infrared photons from dust by the relativistic electrons responsible for the radio synchrotron emission. The production of X-ray emission from ICS allows an estimate of the magnetic field strength of 0.08 mG within the nonthermal filament. This should be an important parameter for any models of the Galactic center nonthermal filaments.     

Radiation from relativistic shocks in turbulent magnetic fields

Using our new 3-D relativistic particle-in-cell (PIC) code parallelized with MPI, we investigated long-term particle acceleration associated with a relativistic electron–positron jet propagating in an unmagnetized ambient electron–positron plasma. The simulations were performed using a much longer simulation system than our previous simulations in order to investigate the full nonlinear stage of the Weibel instability and its particle acceleration mechanism. Cold jet electrons are thermalized and ambient electrons are accelerated in the resulting shocks. Acceleration of ambient electrons leads to a maximum ambient electron density three times larger than the original value as predicted by hydrodynamic shock compression. In the jet (reverse) shock behind the bow (forward) shock the strongest electromagnetic fields are generated. These fields may lead to time dependent afterglow emission. In order to calculate radiation from first principles that goes beyond the standard synchrotron model used in astrophysical objects we have used PIC simulations. Initially we calculated radiation from electrons propagating in a uniform parallel magnetic field to verify the technique. We then used the technique to calculate emission from electrons in a small simulation system. From these simulations we obtained spectra which are consistent with those generated from electrons propagating in turbulent magnetic fields with red noise. This turbulent magnetic field is similar to the magnetic field generated at an early nonlinear stage of the Weibel instability. A fully developed shock within a larger simulation system may generate a jitter/synchrotron spectrum.     

X-ray, γ-emission and energetic particles in near-Earth space as measured by CORONAS-F satellite: From maximum to minimum of the last solar cycle

The Russian solar observatory CORONAS-F was launched into a circular orbit on July 31, 2001 and operated until December 12, 2005. Two main aims of this experiment were: (1) simultaneous study of solar hard X-ray and γ-ray emission and charged solar energetic particles, (2) detailed investigation of how solar energetic particles influence the near-Earth space environment. The CORONAS-F satellite orbit allows one to measure both solar energetic particle dynamics and variations of the solar particle boundary penetration as well as relativistic electrons of the Earth’s outer radiation belt during and after magnetic storms. We have found that significant enhancements of relativistic electron flux in the outer radiation belt were observed not only during strong magnetic storms near solar maximum but also after weak storms caused by high speed solar wind streams. Relativistic electrons of the Earth’s outer radiation belt cause volumetric ionization in the microcircuits of spacecraft causing them to malfunction, and solar energetic particles form an important source of radiation damage in near-Earth space. Therefore, the present results and future research in relativistic electron flux dynamics are very important.     

Summary of the workshop on gamma-ray burst afterglows at the 34th COSPAR meeting

A summary is given of the presentations at the COSPAR workshop on γ-ray bursts with some personal commentary on the contributions, the SN/GRB connection, and on the role of magnetic fields in γ-ray bursts and their afterglows. Of special interest were the accumulated arguments for strong collimation and associated reduction in the total required energy for γ-ray bursts. Significant discussion was also devoted to the issues associated with iron and metal lines in X-ray spectra. It is important to note that some of the afterglows seem to require ambient densities 1 g cm⁻³, rather incompatible with a massive star environment. Of associated difficulty is the fact that few, if any, afterglows seem consistent with the r⁻² wind expected for a massive star model. There are reasons to think that if γ-ray bursts are associated with supernovae they are of Type Ic. This suggests that any wind present might be rich in carbon and oxygen, not hydrogen or helium. If γ-ray bursts are narrowly collimated, then the burst is only probing a small portion of any wind, perhaps just that time-dependent and isotropic structure directly along the rotation axis. The characteristics of “hypernovae” may be the result of orientation effects in a mildly inhomogeneous set of progenitors, rather than requiring an excessive total energy or luminosity. The recent event GRB 021004 provided a rich photometric and spectroscopic record and perhaps the most direct evidence yet for the association of a specific γ-ray burst with a massive star progenitor. If the magnetic field plays a significant role in launching a relativistic γ-ray burst jet from within a collapsing star, then the magnetic field may also play a role in the propagation, collimation, and stability of that jet within and beyond the star. The magneto-rotational instability (MRI) can operate under conditions of moderate rotation. This means that the MRI will be at work generating strong fields exponentially rapidly even as the disk of material begins to form and makes a transition from a non-Keplerian to quasi-Keplerian flow in the collapsar and related models.     

Spectra and time variability of black-hole binaries in the low/hard state

We propose a jet model for the low/hard state of galactic black-hole X-ray sources which explains the energy spectra from radio to X-rays and a number of timing properties in the X-ray domain such as the time lag spectra, the hardening of the power density spectra and the narrowing of the autocorrelation function with increasing photon energy. The model assumes that (i) there is a magnetic field along the axis of the jet, (ii) the electron density in the jet drops inversely proportional to distance, (iii) the jet is “hotter” near its center than at its periphery, and (iv) the electrons in the jet follow a power-law distribution function. We have performed Monte Carlo simulations of Compton upscattering of soft photons from the accretion disk and have found power-law high-energy spectra with photon-number index in the range 1.5–2 and cutoff at a few hundred keV, power-law time lags versus Fourier frequency with index 0.8, and an increase of the rms amplitude of variability and a narrowing of the autocorrelation function with increasing photon energy as they have been observed in Cygnus X-1. The spectrum at long wavelengths (radio, infrared, optical) is modeled to come from synchrotron radiation of the energetic electrons in the jet. We find flat to inverted radio spectra that extend from the radio up to about the optical band. For magnetic field strengths of the order 10⁵–10⁶ G at the base of the jet, the calculated spectra agree well in slope and flux with the observations.     

COMPTEL results on the 1.809 MeV gamma-ray line from the Galactic-center region

The COMPTEL experiment on the Compton Gamma-Ray Observatory is designed to image celestial gamma radiation in the energy range from 0.75–30 MeV within a field of view of 1 steradian. It can locate stronger point sources with an accuracy better than 0.5° and is capable of mapping diffuse emission as well. The Galactic-center region was observed by COMPTEL for several 2-week periods in 1991/1992. These observations show evidence for 1.8 MeV line emission along the Galactic disk (attributed to radioactive ²⁶Al), extending over at least 40 degrees in longitude.     

Modeling the (upper) solar atmosphere including the magnetic field

The atmosphere of the Sun is highly structured and dynamic in nature. From the photosphere and chromosphere into the transition region and the corona plasma-β changes from above to below one, i.e., while in the lower atmosphere the energy density of the plasma dominates, in the upper atmosphere the magnetic field plays the governing role – one might speak of a “magnetic transition”. Therefore the dynamics of the overshooting convection in the photosphere, the granulation, is shuffling the magnetic field around in the photosphere. This leads not only to a (re-)structuring of the magnetic field in the upper atmosphere, but induces also the dynamic reaction of the coronal plasma, e.g., due to reconnection events. Therefore the (complex) structure and the interaction of various magnetic patches is crucial to understand the structure, dynamics and heating of coronal plasma as well as its acceleration into the solar wind.

The present article will emphasize the need for three-dimensional modeling accounting for the complexity of the solar atmosphere to understand these processes. Some advances on 3D modeling of the upper solar atmosphere in magnetically closed as well as open regions will be presented together with diagnostic tools to compare these models to observations. This highlights the recent success of these models which in many respects closely match the observations.     

Increase in relativistic electron flux in the inner magnetosphere: ULF wave mode structure

Pc 5 ULF waves are seen concurrently with the rise in radiation belt fluxes associated with CME magnetic cloud events. A 3D global MHD simulation of the 10–11 January, 1997 event has been analyzed for mode structure and shown to contain field line resonance components, both toroidal and poloidal, with peak power on the nightside during southward IMF conditions. A mechanism for inward radial transport and first-invariant conserving acceleration of relativistic electrons is assessed in the context of ULF mode structure analysis, and compared with groundbased and satellite observations.     

Energetic particle fluxes data base of “CORONAS-I” satellite observations

The data base DB SCR uses data obtained by the SCR instrument package on the CORONAS-I satellite. DB SCR contains information about fluxes of relativistic electrons (0.5–124 MeV), protons (1–300 MeV), nuclei (1–19 MeV/nucl) and γ-radiation (0.1–7 MeV) in the low altitude region (500 km). The time resolution of the data is 2.5 s. Magnetic field parameters (B, magnetic latitude and longitude), L-shell and local times (LT and MLT) are included in DB SCR. Since all parameters are equivalents it is possible to perform the multidimensional analysis for any set of DB SCR parameters. The additional DB SCR software packages may be used to develop different semi-empirical models.     

A unified accretion–ejection paradigm for Black Hole X-ray binaries

We present a unified accretion–ejection picture that explains the different spectral state of Black Hole X-ray binaries (BHXrB) from radio to X/γ-rays. In this view, the central region of BHXrB has a multi-flow configuration which consists in (1) an outer standard accretion disc, (2) an inner magnetized accretion disc driving, (3) a self-collimated electron–proton MHD jet, surrounding and (4) a relativistic electron–positron beam when adequate conditions are met. This picture provides a simple and unified explanation to the various canonical spectral states of BH X-ray binaries, by varying the transition radius r_J between the inner disc driving jets and the outer standard disc. In this framework, large r_J correspond to Quiescent and Hard states while small r_J correspond to Thermal Dominant ones. In between these two extremes, r_J can reach values that switches on the pair cascade process giving birth to a relativistic electron–positron beam. This would correspond to the bright intermediate state.     

Kuafu and the studies of CME initiation

We first briefly review the current trend in the studies of coronal mass ejections (CMEs), then summarize some recent efforts in understanding the CME initiation. Emphasis has been put on the studies of Earth-directed CMEs whose associated surface activity and large scale magnetic source have been well identified. The data analysis by combining the MDI full disc magnetograms, vector magnetograms of active regions, EUV waves and dimmings, non-thermal radio sources, and the SOHO LASCO observations has shed new light in understanding the CME magnetism. However, the current studies seem to invoke new observations in a few aspects: (1) The observations which enable us to trace CMEs from the earliest associated surface activity to its initial acceleration and key development in the low corona in the height of 1–3 R; (2) The imaging spectroscopic observations which can be used to diagnose the early plasma outflow and the line-of-sight velocity in understanding the kinematics of CMEs; (3) The accurate timing from primary magnetic energy release, manifested by chromospheric activity, non-thermal radio bursts, and EUV, X-ray and γ-ray emissions, to the CME initiation, early acceleration and propagation, and the consequences in the interplanetary space and magnetosphere. The Kuafu Mission will meet the basic requirement for the new observations in CME initiation studies and serve as a monitor of space weather of the Sun–Earth system.     

High energy radiation from the direction of the galactic black hole Sgr A

X-ray observations indicate that the Galactic black hole Sgr A^∗ is inactive now, however, we suggest that Sgr A^∗ can become active when a captured star is tidally disrupted and matter is accreted into the black hole. Consequently the Galactic black hole could be a powerful source of relativistic protons with a characteristic energy ∼10⁵² erg per capture. The diffuse GeV and TeV γ-rays emitted in the direction of the Galactic Center (GC) are the direct consequences of p–p collisions of such relativistic protons ejected by very recent capture events occurred ?10⁵ yr ago. On the other hand, the extended electron-positron annihilation line emission observed from GC is a phenomenon related to a large population of thermalized positrons, which are produced, cooled down and accumulated through hundreds of past capture events during a period of ∼10⁷ yr. In addition to explaining GeV, TeV and 511 keV annihilation emissions we also estimate the photon flux of several MeV resulting from in-flight annihilation process.     

冕洞网络的大气模型

本文采用非径向磁流管位形的假设,计算了太阳冕洞网络部分的色球-日冕过渡区的能量平衡模型。所考虑的能量流包括辐射、传导、对流和机械波加热（如阿尔芬波）,计算结果表明在冕洞网络部分的过渡区中,电子温度T和密度N分别比宁静太阳中的值低60%和2倍,而其过渡区的厚度比宁静太阳中的大4倍。这种大气模型可满意地解释T≥105K范围的远紫外观测发射量度的分布。另外我们也发现在冕洞大气的过渡区中,阿尔芬波加热似乎不能忽略,尤其是在冕洞的过渡区底部,它的加热作用可能会超过热传导。在冕洞大气中,由于波动量的淀积而产生的对流能损耗也是重要的,在过渡区底部650km以上,对流能损耗逐渐超过辐射损耗。      

Broad band X-ray properties of GRO J1948+32/KS 1947+300

We present here results obtained from three BeppoSAX observations of the transient X-ray pulsar GRO J1948+32 carried out during the declining phase of its 2000 November–2001 June outburst. Timing analysis of the data clearly shows a 18.7 s pulsation in the X-ray light curves in 0.1–100 keV energy band. The pulse profile of GRO 1948+32 is characterized by a broad peak with a sharp rise followed by a narrow dip. The dip in the pulse profile shows very strong energy dependence. Phase-averaged spectroscopy obtained with three of the BeppoSAX instruments shows that the 0.1–100 keV energy spectrum is described by a Comptonized component, a weak blackbody component (7% of the total emission) for soft X-rays, a narrow and weak iron emission line at 6.7 keV and low column density of material in the line of sight. The results obtained from the analysis are discussed in this paper.     

Diagnosing the storm-time ring current and other magnetospheric plasma domains using relativistic electron data

Ring current ions and relativistic electrons simultaneously measured on board MOLNIYA-1 are analyzed in comparison with the ground-based magnetometer data for the period of a strong magnetic storm (|D_st|max≈230 nT). Injection of >500 keV electrons into the slot region (L≈3) near equatorial plane is occurred on time scale ≈1 hour, when, during the magnetic storm maximum, the extreme low-latitude position of auroral electrojets is reached and ring current becomes more symmetrical. Positions of both the ring current maximum and electron intensity maximum (L_max) are consistent to our previous result: |D_st|_max = 2.75 • 10⁴/L⁴_max. An extreme storm-time low-latitude position of the west electrojet center (for amplitudes of |D_st|_max up to 600 nT) is shown to be in a good consistence with this empirical dependence. It is supposed the trapped radiation boundary collapses down to L≈L_max in the course of the storm main phase.     

Long-term dynamics of the inner Jovian electron radiation belts

Long-term variations of total Jovian synchrotron emission are well known to vary slowly in time. Several hypotheses have been proposed to explain these variations, they can be solar wind driven and/or induced by the geometrical effect of the declination of the Earth in the jovicentric coordinates, D_E. However, until now, not any of them have been definitely proved. We propose here to investigate, this long-term dynamics based on appropriate simulation from a 3D model, Salammbô-3D. This model has been developed to study spatial distribution of electrons in the inner Jovian radiation belts. We will carry out two different approaches, the first one being based on synchrotron simulation from the Salammbô code and the second one being based on GALILEO EPD measurements. Two-dimensional images of Jupiter synchrotron emission can be obtained from our model, for any geometrical configuration (λ_III(CML), D_E). Comparisons show a good agreement between modeling results and VLA observations. With Salammbô-3D, we can also study long-term variations of total Jovian synchrotron emission. The role of the two geometrical factors, λ_III(CML) and D_E, will be analyzed. First, we will present beaming curves (evolution of Jovian synchrotron emission in terms of λ_III(CML)), resulting from the simulation to validate the geometry of the system in the code. Then, the evolution of the non-thermal flux density of synchrotron emission, in terms of D_E, joviographic declination of the Earth, will be studied. With the help of simulations resulting from Salammbô-3D, we will try to discriminate between geometrical induced variations and natural dynamics. On the other hand we will investigate on GALILEO EPD measurements from 1995 until now, restricted to 5–10 Rj, to find out any similarity with the long-term variations of non-thermal flux density of synchrotron emission.     

X-ray synchrotron emission from supernova remnants

X-ray synchrotron emission tells us of the highest energy reached by accelerated electrons. In a few supernova remnants (SN 1006, G347.3-0.5) this is the dominant form of X-ray radiation, but in most it is superposed to the dominant thermal emission. Thanks to the spectro-imaging capability of Chandra and XMM-Newton, X-ray synchrotron emission has now been unambiguously detected in most young supernova remnants (Cas A, Tycho, Kepler). It arises in a very thin shell (a few arcsecs) at the blast wave. The thinness of that shell (much broader in the radio domain) implies that the high energy electrons cool down very fast behind the shock. The magnetic field that one deduces from that constraint is more than 100 μG behind the shock.     

X-ray broad line emission in Seyfert galaxies: Mrk 766 and NGC 4051

Long (>100 ks) observations of the bright Seyfert galaxies Mrk 766 and NGC 4051 have been obtained using XMM-Newton. The RGS 5–38 Å spectra reveal evidence of broad features. These can be modelled with relativistic emission lines coming from the immediate vicinity of a massive rotating black hole. Lines of OVIII, NVII and CVI are required to reproduce the spectrum of Mrk 766, whereas the spectrum of NGC 4051 can be modelled using a single, even broader OVIII line. Both Seyferts also exhibit broad iron line emission in the 2–8 keV range, and the data available thus far suggest that the strength of the low-energy emission lines and the strength of the iron line may be correlated.     

XMM-Newton observations of low luminosity Be/X-ray candidates

A small number of early Be stars exhibit X-ray luminosities intermediate between those typical of early type stars and those radiated by Be/X-ray binaries in the quiescent state. We report on XMM-Newton observations of two such Be stars, HD 161103 and SAO 49725 which were originally discovered in a systematic cross-correlation between the ROSAT all-sky survey and SIMBAD. The new observations confirm the X-ray luminosity detected by ROSAT (L_X  10³² erg s⁻¹) and the hardness of their X-ray spectra (thin thermal with kT  8–10 keV or power law with photon index of 1.7) which are both unusual for normal early type stars. We discuss the possible origin of this excess X-ray emission in the light of the models proposed for γ-Cas, magnetic disc-star interaction or accretion onto a compact companion object, neutron star or white dwarf, and compare the properties of these two sources with those of the new massive systems discovered in the XMM- Newton/SSC survey of the Galactic plane.