X-ray Jet Research Articles

X-ray jets and magnetic flux emergence in the Sun

AbstractMagnetized plasma is emerging continually from the solar interior into the atmosphere. Magnetic flux emergence events and their consequences in the solar atmosphere are being observed with high space, time and spectral resolution by a large number of space missions in operation at present (e.g. SOHO, Hinode, Stereo, Rhessi). The collision of an emerging and a preexisting magnetic flux system in the solar atmosphere leads to the formation of current sheets and to field line reconnection. Reconnection under solar coronal conditions is an energetic event; for the field strengths, densities and speeds involved in the collision of emerging flux systems, the reconnection outflows lead to launching of high-speed (hundreds of km/s), high-temperature (107 K) plasma jets. Such jets are being observed with the X-Ray and EUV detectors of ongoing satellite missions. On the other hand, the spectacular increase in computational power in recent years permits to carry out three-dimensional numerical experiments of the time evolution of flux emerging systems and the launching of jets with a remarkable degree of detail.In this review, observation and modeling of the solar X-Ray jets are discussed. A two-decade long computational effort to model the magnetic flux emergence events by different teams has led to numerical experiments which explain, even quantitatively, many of the observed features of the X-ray jets. The review points out that, although alternative mechanisms must be considered, flux emergence is a prime candidate to explain the launching of the solar jets.

A new interesting source in Chandra field: a pulsar wind nebula?

Abstract We report the detection of a point source CXO J172337.5−373442 in a Chandra field with a high significance (26.7σ), and the discovery (4σ) of a 48 arcsec long X-ray tail emanating from the point source. The X-ray spectra of both the point source and the tail are well described with a single absorbed power law, and the tail is harder (power-law index Γ= 0.14+0.59−0.68) than the point source (Γ= 1.78+0.13−0.11). From this first detailed spatial, spectral and timing X-ray analysis of CXO J172337.5−373442, and from a plausible optical counterpart found from the archives, we conclude that this source is either a Galactic high-mass X-ray binary with an X-ray jet or a Galactic pulsar with its ‘pulsar wind nebula’ seen as the X-ray tail. Although the currently available data are not enough to distinguish between these two candidates with certainty, a detailed comparison of their known properties with those of CXO J172337.5−373442 favours the latter type. If this identification is correct, then the pulsar should be middle-aged or old, that has escaped from its supernova remnant, and the X-ray tail should originate from the synchrotron emission from either of the following locations: (i) a shocked region or (ii) a jet emanating from the pulsar's magnetosphere.

ChandraReveals Twin X‐Ray Jets in the Powerful FR II Radio Galaxy 3C 353

We report X-ray imaging of the powerful FR II radio galaxy 3C 353 using the Chandra X-Ray Observatory. Due to 3C 353's two -->4' ' wide and -->2' long jets we are able to study in detail the internal structure of the large-scale relativistic outflows at both radio and X-ray photon energies with the subarcsecond spatial resolution provided by the VLA and Chandra instruments. In a 90 ks Chandra observation, we have detected X-ray emission from most radio structures in 3C 353, including the nucleus, the jet and the counterjet, the terminal jet regions (hot spots), and one radio lobe. We show that the detection of the X-ray emission associated with the radio knots and counterknots, which is most likely nonthermal in origin, puts several crucial constraints on the X-ray emission mechanisms in powerful large-scale jets of quasars and FR II sources. In particular, we show that this detection is inconsistent with the inverse-Compton model proposed in the literature and instead implies a synchrotron origin of the X-ray jet photons. We also find that the width of the X-ray counterjet is possibly narrower than that measured in radio bands, that the radio to X-ray flux ratio decreases systematically downstream along the jets, and that there are substantial (kpc-scale) offsets between the positions of the X-ray and radio intensity maxima within each knot, whose magnitudes increase away from the nucleus. We discuss all these findings in the wider context of the physics of extragalactic jets, proposing some particular although not definitive solutions or interpretations for each problem. In general, we find that the synchrotron X-ray emission of extragalactic large-scale jets is not only shaped by the global hydrodynamical configuration of the outflows, but is also likely to be very sensitive to the microscopic parameters of the jet plasma. A complete, self-consistent model for the X-ray emission of extragalactic jets still remains elusive.

Magnetic flux cancellation associated with a recurring solar jet observed withHinode,RHESSI, andSTEREO/EUVI

Aims. We study the physical properties of a recurring solar active region jet observed in X-rays and extreme-ultraviolet (EUV).Methods. Multi-wavelength data from all three instruments on board Hinode were analysed. X-ray imaging and spectroscopy of the microflaring emission associated with the jets was performed with the Reuven Ramaty High Energy Spectroscopic Imager (RHESSI ). Associated EUV jets were observed with the Sun Earth Connection Coronal and Heliospheric Investigation (SECCHI)/Extreme Ultraviolet Imager (EUVI) on board STEREO .Results. We found a correlation between recurring magnetic flux cancellation close to a pore, the X-ray jet emission, and associated Ca II H ribbon brightenings. We estimated the lower limit for the decrease in magnetic energy associated with the X-ray jet emission at 3 1029 erg. The recurring plasma ejection was observed simultaneously at EUV and X-ray temperatures, associated with type III radio bursts and microflaring activity at the jet footpoint.Conclusions. The recurring jet (EUV and X-ray) emissions can be attributed to chromospheric evaporation flows due to recurring coronal magnetic reconnection. In this process, the estimated minimum loss in the magnetic energy is sufficient to account for the total energy required to launch the jet.

A Kiloparsec‐Scale X‐Ray Jet in the BL Lac Source S5 2007+777

X-ray jets in AGNs are commonly observed in FR II and FR I radio galaxies, but rarely in BL Lac objects, most probably due to their orientation close to the line of sight and the ensuing foreshortening effects. Only three BL Lac objects are known so far to contain a kpc-scale X-ray jet. In this paper we present the evidence for the existence of a fourth extended X-ray jet in the classical radio-selected source S5 2007+777, which for its hybrid FR I and FR II radio morphology has been classified as a HYMOR (HYbrid MOrphology Radio source). Our Chandra ACIS-S observations of this source revealed an X-ray counterpart to the 19'' long radio jet. Interestingly, the X-ray properties of the kpc-scale jet in S5 2007+777 are very similar to those observed in FR II jets. First, the X-ray morphology closely mirrors the radio one, with the X-rays being concentrated in the discrete radio knots. Second, the X-ray continuum of the jet/brightest knot is described by a very hard power law, with photon index ΓX ~ 1, although the uncertainties are large. Third, the optical upper limit from archival HST data implies a concave radio-to-X-ray SED. If the X-ray emission is attributed to IC/CMB with equipartition, strong beaming (δ = 13) is required, implying a very large scale (Mpc) jet. The beaming requirement can be somewhat relaxed assuming a magnetic field lower than equipartition. Alternatively, synchrotron emission from a second population of very high-energy electrons is viable. Comparison to other HYMOR jets detected with Chandra is discussed, as well as general implications for the origin of the FR I/FR II division.

X‐Ray Properties of the Gigahertz Peaked and Compact Steep Spectrum Sources

We present Chandra X-ray Observatory observations of gigahertz peaked-spectrum (GPS) and compact steep spectrum (CSS) radio sources. The Chandra sample contains 13 quasars and 3 galaxies, with measured 2-10 keV X-ray luminosities within 1042-1046 erg s−1. We detect all of the sources, five of which are observed in X-rays for the first time. We study the X-ray spectral properties of the sample. The measured absorption columns in the quasars are different from those in the galaxies in that the quasars show no absorption (with limits ~1021 cm−2), while the galaxies have large absorption columns (>1022 cm−2) consistent with previous findings. The median photon index of the sources with a high signal-to-noise ratio is Γ = 1.84 ± 0.24, which is larger than the typical index of radio-loud quasars. The arcsec resolution of the Chandra telescope allows us to investigate extended X-ray emission and to look for diffuse components and X-ray jets. We found X-ray jets in two quasars (PKS 1127–145 and B2 0738+32), and an X-ray cluster surrounding a CSS quasar (3C 186; z = 1.1). We detected a possible binary structure in galaxy 0941–080 and an extended diffuse emission in galaxy PKS B1345+125. We discuss our results in the context of X-ray emission processes and radio source evolution. We conclude that the X-ray emission in these sources is most likely unrelated to a relativistic jet, although the sources' radio loudness may suggest a high radiative efficiency for the jet power in these sources.

SSC SCENARIO FOR TEV EMISSION FROM NON-BLAZAR AGNs

M 87 is the first extragalactic source detected in the TeV γ-ray domain that is not a blazar, its large scale jet not being aligned to the line of sight. We present here a multi-blob synchrotron self-Compton model accounting explicitly for large viewing angles and moderate Lorentz factors as inferred from magnetohydrodynamic simulations of jet formation, motivated by the detection of M 87 at very high energies (VHE; E > 100 GeV ). Predictions are presented for the very high-energy emission of active galactic nuclei with extended optical or X-ray jet, which could be misaligned blazars but still show some moderate beaming. We include predictions for 3C 273, Cen A and PKS 0521–36.

Formation of single pinched plasma point in the cathode plasma jet of a multipicosecond laser-triggered vacuum discharge

Characteristics of cathode plasma jet pinching and x-ray emission from a multipicosecond laser-triggered vacuum discharge are presented. Discharge was created in between a planar Al cathode and a conical point-tip Ti anode (separation: 2-15 mm, circuit inductance of approximately 0.53 microH, peak discharge current of approximately 3 kA, and rise time of approximately 400 ns). For anode-cathode separation of approximately 13.5 mm, only a single pinched plasma point was formed in the cathode plasma jet at a distance of approximately 9.5 mm from the cathode. Quantitative analysis of the x-ray signals recorded using a pin diode with different filters and viewing different regions of the discharge, shows soft ( approximately keV photon energy) x-ray emission from the plasma point with a flux of approximately (3-5)x10(10) photons/sr, and multi-keV x-ray emission from the Ti anode with Kalpha ( approximately 4.51 keV) photon flux of approximately 10(10) photons/sr.

DETECTION OF A RELIC X-RAY JET IN CYGNUS A

We present a 200 ks Chandra ACIS-I image of Cygnus A, and discuss a long linear feature seen in its counterlobe. This feature has a nonthermal spectrum and lies on the line connecting the brighter hotspot on the approaching side and the nucleus. We therefore conclude that this feature is (or was) a jet. However, the outer part of this X-ray jet does not trace the current counterjet observed in radio. No X-ray counterpart is observed on the jet side. Using light-travel time effects we conclude that this X-ray 50 kpc linear feature is a relic jet that contains enough low-energy plasma (γ ~ 103) to inverse-Compton scatter cosmic microwave background photons, producing emission in the X-rays.

Aligned Molecular Clouds towards SS 433 and L = 348${\rlap{\hskip.75pt{^\circ}}\hskip.75pt.\hskip1pt}$5: Possible Evidence for a Galactic “Vapor Trail” Created by a Relativistic Jet

Abstract We carried out a detailed analysis of the NANTEN $^{12}$CO ($J=$ 1–0) dataset in two large areas towards SS 433 ($l \sim$ 40$^\circ$) and $l \sim$ 348${\rlap{\hskip.75pt{^\circ}}\hskip.75pt.\hskip1pt}$5. In SS 433, we detected ten clouds, which are well aligned nearly along the axis of an X-ray jet emanating from SS 433 at $V_{\rm LSR}$ = 42–56 km s$^{-1}$. The total length of the feature is $\sim\;$300 pc, three-times longer than that of the X-ray jet, at 3 kpc. Towards $l \sim$348${\rlap{\hskip.75pt{^\circ}}\hskip.75pt.\hskip1pt}$5, we detected four aligned clouds at $V_{\rm LSR}$ = $-$80–$-$100 km s$^{-1}$, nearly perpendicular to the Galactic plane. The total length of the feature is $\sim\;$400 pc at 6 kpc. In both cases, the CO clouds are distributed at $\mid{b}\mid\;\sim$ 1${}^\circ$–5${}^\circ$ and their alignments and coincidence in velocity should be rare, suggesting that they are physically associated. We present a scenario to explain these aligned clouds in which the interaction between a relativistic jet and the interstellar medium induced molecular cloud formation over the last $\sim\;$10$^{5\hbox{--}6}$yr. It is suggested that the timescale of the relativistic jet may be considerably larger, on the order of 10$^{5\hbox{--}6}$yr, than previously thought in SS 433. The driving engine of the jet is obviously SS 433, itself, in SS 433, although the engine is not yet identified in $l \sim$348${\rlap{\hskip.75pt{^\circ}}\hskip.75pt.\hskip1pt}$5 among possible several candidates detected in X-rays and TeV gamma rays.

The nature of the soft X-ray source in DG Tauri

The classical T Tauri star DG Tau shows all typical signatures of X-ray activity and, in particular, harbors a resolved X-ray jet. DG Tau’s jet is one of the most well studied jets of young stellar objects, having been observed for more than 25 years by a variety of instruments. We demonstrate that its soft and hard X-ray components are separated spatially by approximately 0.2 arcsec by deriving the spatial offset between both components from the event centroids of the soft and hard photons utilizing the intrinsic energyresolution of the Chandra ACIS-S detector. We also demonstrate that this offset is physical and cannot be attributed to an instrumental origin or to low counting statistics. Furthermore, the location of the derived soft X-ray emission peak coincides with emission peaks observed for optical emission lines, suggesting that both soft X-rays and optical emission have the same physical origin.

Evidence for Polar Jets as Precursors of Polar Plume Formation

Observations from the Hinode/XRT telescope and STEREO/SECCHI/EUVI are utilized to study polar coronal jets and plumes. The study focuses on the temporal evolution of both structures and their relationship. The data sample, spanning 2007 April 7-8, shows that over 90% of the 28 observed jet events are associated with polar plumes. EUV images (STEREO/SECCHI) show plume haze rising from the location of approximately 70% of the polar X-ray (Hinode/XRT) and EUV jets, with the plume haze appearing minutes to hours after the jet was observed. The remaining jets occurred in areas where plume material previously existed, causing a brightness enhancement of the latter after the jet event. Short-lived, jetlike events and small transient bright points are seen (one at a time) at different locations within the base of preexisting long-lived plumes. X-ray images also show instances (at least two events) of collimated thin jets rapidly evolving into significantly wider plumelike structures that are followed by the delayed appearance of plume haze in the EUV. These observations provide evidence that X-ray jets are precursors of polar plumes and in some cases cause brightenings of plumes. Possible mechanisms to explain the observed jet and plume relationship are discussed.

ChandraObservation of Cir X‐1 near the Periastron Passage: Evidence for an X‐Ray Jet?

We present the results of a 25 ks long Chandra observation of the peculiar source Cir X-1 near the periastron passage. We report precise X-ray coordinates of the source, which were compatible with the optical and radio counterpart coordinates. We focus on the study of the detected emission features using the High Energy Transmission Grating Spectrometer on board the Chandra satellite. We detect emission lines associated with Mg XII, Si XIII, Si XIV, S XV, S XVI, Ar XVII, Ar XVIII, Ca XIX, Ca XX, Fe XXV, and Fe XXVI, showing an average redshift of 470 km s−1. The most intense emission features can be fitted with two lines; this is more evident for the 6.6 keV emission feature, which shows a double-peaked structure. We propose that the redshifted and blueshifted lines of Mg XII, Si XIV, S XVI, and Fe XXV can be interpreted as emission from a blue and red beam of an X-ray jet, finding that the angle between the line of sight and the jet direction is 92° and the jet velocity is 0.08c.

An active region jet observed with Hinode

Aims. We study the physical properties of an active region (AR) jet in order to probe the mechanisms responsible for it. Methods. We report 2007 January 15/16 observations of a recurring jet situated on the west side of NOAA AR 10938. Multiwavelength data from all three instruments onboard Hinode were analysed. This paper focuses on one instance of a jet observed with the Hinode/EUV Imaging Spectrometer (EIS). Using EIS raster data we measured the temperatures, Doppler shifts, density, and filling factor. Results. A strong blue-shifted component and an indication of a weak red-shifted component at the base of the jet was observed around Log Te = 6.2. The up-flow velocities exceeded 150 km s −1 . The jet component was seen over a range of temperatures between 5.4 and 6.4 in Log Te .U sing Fexii λ186 and λ195 line ratios, we measured densities above Log Ne = 11 for the high-velocity up-flow component. We found that the density of the high-velocity up-flow increases with velocity. We estimate the filling factor in the jet upflow to be <0.03. With the Hinode/Solar Optical Telescope (SOT), we observed recurrent (quasi periodic) magnetic flux cancelations just before the recurrent jet emission was seen in images taken with the X-ray Telescope (XRT). Conclusions. The high-velocity up-flows, together with the density dependence on velocity, support an evaporation scenario for the acceleration of this jet. The high density and small filling factor, coupled with the high Doppler velocities are strongly suggestive of multiple small-scale magnetic reconnection events being responsible for the production of both EUV and X-ray jets.

Discovery of a bipolar X-ray jet from the T Tauri star DG Tauri

Aims. We have obtained and analyzed Chandra ACIS-S observations of the strongly accreting classical T Tauri star DG Tau. Our principal goals are to map the immediate environment of the star to characterize possible extended X-rays formed in the jet, and to re-visit the anomalous, doubly absorbed X-ray spectrum of DG Tau itself. Methods. We combine our new ACIS-S data with a data set obtained previously. The data are superimposed to obtain flux and hardness images. Separate X-ray spectra are extracted for DG Tau and areas outside its point spread function. Results. We detect a prominent X-ray jet at a position angle of PA ≈ 225 deg (tentatively suggested by Gudel et al. 2005, ApJ, 626, L53), coincident with the optical jet axis. We also identify a counter jet at PA = 45 deg. The X-ray jets are detected out to a distance of ≈5 �� from the star, their sources being extended at the ACIS-S resolution. The jet spectra are soft, with a best-fit electron temperature of 3.4 MK. We find evidence for excess absorption of the counter jet. The spectrum of the DG Tau point source shows two components with largely different temperatures and absorption column densities. Conclusions. The similar temperatures and small absorbing gas columns of the jet sources and the soft component of the “stellar” source suggest that these sources are related, produced either by shocks or by magnetic heating in the jets. Cooling estimates suggest that the pressure in the hot gas contributes to jet expansion. The hard “stellar” component, on the other hand, is associated with a stellar corona or magnetosphere. The excessive photoelectric absorption of this component suggests the presence of dust-depleted accretion streams above coronal magnetic fields.

Evidence for Alfvén Waves in Solar X-ray Jets

Coronal magnetic fields are dynamic, and field lines may misalign, reassemble, and release energy by means of magnetic reconnection. Giant releases may generate solar flares and coronal mass ejections and, on a smaller scale, produce x-ray jets. Hinode observations of polar coronal holes reveal that x-ray jets have two distinct velocities: one near the Alfvén speed ( approximately 800 kilometers per second) and another near the sound speed (200 kilometers per second). Many more jets were seen than have been reported previously; we detected an average of 10 events per hour up to these speeds, whereas previous observations documented only a handful per day with lower average speeds of 200 kilometers per second. The x-ray jets are about 2 x 10(3) to 2 x 10(4) kilometers wide and 1 x 10(5) kilometers long and last from 100 to 2500 seconds. The large number of events, coupled with the high velocities of the apparent outflows, indicates that the jets may contribute to the high-speed solar wind.

Fine Structures of Solar X-Ray Jets Observed with the X-Ray Telescope aboard Hinode

Abstract The X-Ray Telescope (XRT) aboard Hinode has revealed the fine structure of solar X-ray jets. One of the fine structures observed by XRT is an expanding loop. The loop appeared near the footpoint of the jet when footpoint brightening was observed. Additionally, we have found that the X-ray jets began just after the expanding loop “breaks”. Other fine structures discovered by XRT are thread-like features along the axis of the jets. XRT has shown that these thread structures compose the cross-section of jets. The fine structures and their motions strongly support an X-ray jet model based on magnetic reconnection, and also suggest that we must consider the three-dimensional configuration of the magnetic field to understand the jet phenomenon. We also investigated the reverse jet associated with the X-ray jet in the quiet Sun, and propose that the reverse jet is produced by heat conduction, or a MHD wave subsequent to the main jet.

Small-Scale X-Ray/EUV Jets Seen in Hinode XRT and TRACE

Abstract We present the morphological and kinematic characteristics of three small-scale X-ray/EUV jets simultaneously observed by the Hinode XRT and the TRACE. For this, we examined all XRT movies with a thin Al/Poly filter from 2006 October 20 to 2007 April 8, and then found 34 small-scale eruptions. We next took a look at the corresponding TRACE 171/195 Å images associated with the eruptions. As a result, we found three simultaneous X-ray and EUV jets. For two different bands, they have similar characteristics in terms of the projected speed (90–310 km s$^{-1}$), lifetime (100–2000 s), and size (1.1–5$\times$10$^5$km). These characteristics are similar to the previous results by the Yohkoh SXT, but are quite different from EUV jets associated with H$\alpha$ surges. From the EUV Imaging Spectrometer, four spectral lines for the last event, we found blueshift (up to $-$64 km s$^{-1}$) and redshift (up to 20 km s$^{-1}$) motions as well as nonthermal velocities ranging from 57 to 106 km s$^{-1}$ at the jet footpoint. We note a tendency: the hotter the maximum ionization temperature is, the smaller the area of blueshift region is. These characteristics are consistent with a typical jet model that includes the magnetic reconnection between open coronal fields and emerging magnetic fields.

A Study of Polar Jet Parameters Based on Hinode XRT Observations

Abstract Hinode/SOHO campaign 7197 is the most extensive study of polar jet formation and evolution from within both the north and south polar coronal holes so far. For the first time, this study showed that the appearance of X-ray jets in the solar coronal holes occurs at very high frequency–about 60 jets d$^{-1}$ on average. Using observations collected by the X-Ray Telescope on Hinode, a number of physical parameters from a large sample of jets were statistically studied. We measured the apparent outward velocity, the height, the width and the lifetime of the jets. In our sample, all of these parameters show peaked distributions with maxima at 160 km s$^{-1}$ for the outward velocity, 5$\times$10$^4$km for the height, 8$\times$10$^3$km for the width, and about 10 min for the lifetime of the jets. We also present the first statistical study of jet transverse motions, which obtained transverse velocities of 0–35 km s$^{-1}$. These values were obtained on the basis of a larger (in terms of frequency) and better sampled set of events than what was previously statistically studied (Shimojo et al. 1996, PASJ, 48, 123). The results were made possible by the unique characteristics of XRT. We describe the methods used to determine the characteristics and set some future goals. We also show that despite some possible selection effects, jets preferably occur inside the polar coronal holes.

Echo Emission from Dust Scattering and X‐Ray Afterglows of Gamma‐Ray Bursts

We investigate the effect of X-ray echo emission in gamma-ray bursts (GRBs). We find that the echo emission can provide an alternative way of understanding X-ray shallow decays and jet breaks. In particular, a shallow decay followed by a "normal" decay and a further rapid decay of X-ray afterglows can be together explained as being due to the echo from prompt X-ray emission scattered by dust grains in a massive wind bubble around a GRB progenitor. We also introduce an extra temporal break in the X-ray echo emission. By fitting the afterglow light curves, we can measure the locations of the massive wind bubbles, which will bring us closer to finding the mass loss rate, wind velocity, and the age of the progenitors prior to the GRB explosions.