Search

We succeeded in observing two large spicules simultaneously with the Atacama Large Millimeter/submillimeter Array (ALMA), the Interface Region Imaging Spectrograph (IRIS), and the Atmospheric Imaging Assembly (AIA) onboard the Solar Dynamics Observatory. One is a spicule seen in the IRIS Mg II slit-jaw images and AIA 304\AA\ images (MgII/304A spicule). The other one is a spicule seen in the 100GHz images obtained with ALMA (100GHz spicule). Although the 100GHz spicule overlapped with the MgII/304A spicule in the early phase, it did not show any corresponding structures in the IRIS Mg II and AIA 304A images after the early phase. It suggests that the spicules are individual events and do not have a physical relationship. To obtain the physical parameters of the 100GHz spicule, we estimate the optical depths as a function of temperature and density using two different methods. One is using the observed brightness temperature by assuming a filling factor, and the other is using an emission model for the optical depth. As a result of comparing them, the kinetic temperature of the plasma and the number density of ionized hydrogens in the 100GHz spicule are ~6800 K and 2.2 x 10^10 cm^-3. The estimated values can explain the absorbing structure in the 193A image, which appear as a counterpart of the 100GHz spicule. These results suggest that the 100GHz spicule presented in this paper is classified to a macrospicule without a hot sheath in former terminology., Comment: 8 pages, 4 figures, Accepted to ApJL

著者人数: 35名 (所属. 宇宙航空研究開発機構宇宙科学研究所(JAXA)(ISAS): 坂尾, 太郎; 清水, 敏文), Number of authors: 35 (Affiliation. Institute of Space and Astronautical Science, Japan Aerospace Exploration Agency(JAXA)(ISAS): Sakao, Taro; Shimizu, Toshifumi), Accepted: 2019-08-01, 資料番号: SA1190166000

資料番号: SA1004443000

The X-ray Telescope (XRT) aboard the Hinode satellite is a grazing incidence X-ray imager equipped with a 2048×2048 CCD. The XRT has 1 arcsec pixels with a wide field of view of 34×34 arcmin. It is sensitive to plasmas with a wide temperature range from < 1 to 30 MK, allowing us to obtain TRACE-like low-temperature images as well as Yohkoh/SXT-like high-temperature images. The spacecraft Mission Data Processor (MDP) controls the XRT through sequence tables with versatile autonomous functions such as exposure control, region-of-interest tracking, flare detection, and flare location identification. Data are compressed either with DPCM or JPEG, depending on the purpose. This results in higher cadence and/or wider field of view for a given telemetry bandwidth. With a focus adjust mechanism, a higher resolution of Gaussian focus may be available on-axis. This paper follows the first instrument paper for the XRT (Golub et al., Solar Phys. 243, 63, 2007) and discusses the design and measured performance of the X-ray CCD camera for the XRT and its control system with the MDP.

著者人数：15名, Accepted: 2007-09-11, 資料番号: SA1000268000

Accepted: 2007-08-17, 資料番号: SA1000267000

著者人数：25名, Accepted: 2007-07-30, 資料番号: SA1000203000

We present the H$\alpha$ observations from ARIES, Nainital of a compact and impulsive solar flare occurred on March 10, 2001 and associated with a CME. We have also analysed HXT, SXT/Yohkoh observations as well as radio observations from Nobeyama Radio Observatory to derive the energetics and dynamics of this impulsive flare. We co-align the H$\alpha$, SXR, HXR, MW and magnetogram images within the instrumental spatial resolution limit. We detect a single HXR source in this flare, which is found spatially associated with one of the H$\alpha$ bright kernel. The unusual feature of HXR and H$\alpha$ sources, observed for the first time, is the rotation during the impulsive phase in clockwise direction. We propose that the rotation may be due to asymmetric progress of the magnetic reconnection site or may be due to the change of peak point of the electric field. In MW emission we found two sources, one is main source which is at the main flare site and another is remote source located in South-West direction. It appears that the remote source is formed by the impact of accelerated energetic electrons from the main flare site. From the spatial co-relation of multi-wavelength images of th, Comment: Accepted in Solar Physics, 20 pages, 12 Figures

Coronal hard X-ray (HXR) sources were discovered by the Yohkoh HXT telescope in about two dozen limb flares: Impulsive and gradual ones. On the basis of HXT data, we investigated the spatial evolution of coronal sources. Slow ascending motions of sources are seen in several flares. In five events, it was possible to estimate the velocity of the upward motion with values between 10 and 30 km/s. We present these observational results and conclude that coronal source motions should be studied statistically using the RHESSI high-resolution HXR imaging data. We discuss the possibility that coronal HXR emission is generated as bremsstrahlung of the fast electrons accelerated in collapsing magnetic traps due to joint action of the Fermi-type first-order mechanism and betatron acceleration.

Using the Yohkoh Hard X-Ray Telescope (HXT) data, we have examined motions of the hard X-ray (HXR) sources during 72 solar flares occurred from 1991 September to 2001 December. In these flares, we have found 198 intense sources that are presumably the chromospheric footpoints (FPs) of flare loops. The average velocity V and the velocity dispersion σ were determined by a linear regression for these sources. For 80% of them, the ratio of V to 3 σ is larger than 1, strongly suggesting that the regular motions of the HXR sources dominate their chaotic motions. For 43 of 72 flares, coalignment of the HXT images with the photospheric magnetograms allows us to consider the HXR sources located on the both sides of the photospheric neutral line (NL) as the FP sources, and to distinguish between three main types of the FP motions. The type I is the motions of the HXR sources preferentially away from and nearly perpendicular to the NL. Less than 5% of the flares show this pattern of motion. In the type II, the sources move mainly along the NL in anti-parallel directions. Such motions have been found in 26% of flares. The type III involves a similar pattern of motions as the type II but all the HXR sources move in the same direction along the NL. Flares of this type constitute 30% of the flares. About 19% of flares can be described as a combination of these basic types. The remaining 20% of flares seem to be more complicated or less regular in the motion scale under consideration. An interpretation of results is suggested.

We present the results of a detailed analysis of multi-wavelength observations of a very impulsive solar flare 1B/M6.7, which occurred on 10 March, 2001 in NOAA AR 9368 (N27 W42). The observations show that the flare is very impulsive with very hard spectrum in HXR that reveal non-thermal emission was most dominant. On the other hand this flare also produced type II radio burst and coronal mass ejections (CME), which are not general characteristics for impulsive flares. In H$\alpha$ we observed the bright mass ejecta (BME) followed by drak mass ejecta (DME). Based on the consistence of the onset times and direction of BME and CME, we conclude that these two phenomena are closely associated. It is inferred that the energy build-up took place due to photospheric reconnection between emerging positive parasitic polarity and predominant negative polarity, which resulted as a consequence of flux cancellation. The shear increased to $>80^o$ due to further emergence of positive parasitic polarity causing strongly enhanced cancellation of flux. It appears that such enhanced magnetic flux cancellation in a strongly sheared region triggered the impulsive flare., Comment: 14 pages, 8 Figures, Accepted for the publication in Solar Physics

The tip-tilt mirror (TTM) system was developed for the extreme ultraviolet (XUV) Cassegrain telescope aboard the Institute of Space and Astronautical Science sounding rocket. The spatial resolution of the telescope is about 5 arcsec, whereas the rocket pointing is only controlled to be within ±0.5 deg of the target (sun) without additional stability control. To stabilize the XUV image within about 5 arcsec on the focal plane, the TTM system controls the tilt of the secondary mirror with two-axis fixed-coil magnetic actuators. The TTM system has a wide tilt angle and can drive the large secondary mirror at high frequency. The two position-sensitive detectors, one placed in the telescope and the other in the TTM mechanical structure, are used for closed-loop control of the TTM. The closed-loop control system, which has command and telemetry, is executed by the flight software on the digital signal processor. The TTM has a launch-lock mechanism to protect against launch vibrations up to about 16G. The sounding rocket was launched from the Kagoshima Space Center on 31 January 1998. The TTM worked perfectly during the flight and achieved better than the expected 5-arcsec stability on the focal plane during CCD charge-coupled device exposures.

A suite of images from the XUV Doppler Telescope (XDT), the Yohkoh Soft X-ray Telescope (SXT), and the Extreme-Ultraviolet Imaging Telescope (EIT) on the Solar and Heliospheric Observatory (SOHO) allow us to see the whole (T > 1 MK) temperature evolution of coronal loops. The detailed morphological comparison of an active region shows that hot loops seen in SXT (T > 3 MK) and cool loops seen in the the EIT 195 A band (T ~ 1.5 MK) are located in almost alternating manner. The anticoincidence of the hot and the cool loops is conserved for a duration much longer than the estimated cooling timescale. However, both hot and cool loops have counterparts in the intermediate-temperature images. The cross-correlation coefficients are higher for neighboring temperature pairs and lower for pairs with larger temperature differences. These results suggest that loops are not isothermal but rather have a differential emission measure distribution of modest but finite width that peaks at different temperatures for different loops.

On the basis of Yohkoh Hard X-Ray Telescope data and the magnetograms taken by the SOHO Michelson Doppler Imager and the Solar Magnetic Field Telescope at Huairou Solar Observing Station, we suggest an interpretation of the well-observed "Bastille Day 2000" flare. The large-scale structure and dynamics of the flare, as seen in hard X-rays, can be explained in terms of the three-dimensional reconnection at a separator in the corona. More specifically, we suggest that before occurrence of two-ribbon flares with significant decrease of a distance between the hard X-ray (HXR) footpoints, like the Bastille Day flare, the bases of magnetic field separatrices are moved by the large-scale photospheric flows of two types. First, the shear flows, which are parallel to the photospheric neutral line, increase the length of field lines in the corona and produce an excess of magnetic energy. Second, the converging flows, i.e., the flows directed to the neutral line, create the preflare current layers in the corona and provide an excess of energy sufficient to produce a large flare. During the flare, both excesses of magnetic energy are released completely or partially. In the Bastille Day flare, the model describes two kinds of apparent motions of the HXR kernels. One is an increase of a distance between the flare ribbons in which the HXR kernels appear. The effect results from fast reconnection in a coronal current layer. The second effect is a decrease of the distance between the kernels moving to each other as a result of relaxation of magnetic tensions generated by the photospheric shear flows.

The Yohkoh data on the site and mechanism of magnetic energy transformation into kinetic and thermal energies of a superhot plasma at the Sun require new models of reconnection under conditions of highlyanomalous resistivity, which are similar to that one observed in toroidal devices performed to study turbulent heating of a collisionless plasma, and its anomalous heat-conductive cooling. The models make intelligible the observed properties of the three-dimensional reconnection in solar flares.

Particle acceleration is one of the most significant features that are ubiquitous among space and cosmic plasmas. It is most prominent during flares in the case of the Sun, with which huge amount of electromagnetic radiation and high-energy particles are expelled into the interplanetary space through acceleration of plasma particles in the corona. Though it has been well understood that energies of flares are supplied by the mechanism called magnetic reconnection based on the observations in X-rays and EUV with space telescopes, where and how in the flaring magnetic field plasmas are accelerated has remained unknown due to the low plasma density in the flaring corona. We here report the first observational identification of the energetic non-thermal electrons around the point of the ongoing magnetic reconnection (X-point); with the location of the X-point identified by soft X-ray imagery and the localized presence of non-thermal electrons identified from imaging-spectroscopic data at two microwave frequencies. Considering the existence of the reconnection outflows that carries both plasma particles and magnetic fields out from the X-point, our identified non-thermal microwave emissions around the X-point indicate that the electrons are accelerated around the reconnection X-point. Additionally, the plasma around the X-point was also thermally heated up to 10 MK. The estimated reconnection rate of this event is ~0.017., 24 pages, 8 figures, accepted for publication in The Astrophysical Journal

It is observed in impulsive flares with the Hard X-ray Telescope (HXT) onboard Yohkoh that a hard X-ray source is located above the apex of a soft X-ray flaring loop in addition to double footpoint sources (Masuda et al. 1994, 1995). This observation suggests that the flare energy-release, probably magnetic reconnection, takes place not in the soft X-ray loop, but above the loop. It is important to derive the hard X-ray spectrum of this source accurately in order to understand how electrons are energized there. Using an improved image-synthesis technique with new modulation patterns (Sato 1997), we obtained hard X-ray images of the 13 January 1992 flare in the four HXT energy bands with a common photon-accumulation time. The spectrum of the above-the-looptop source in the energy range of 14–93 keV seems to be well fit by emission from an isothermal plasma whose temperature is about 100 MK, rather than by a non-thermal, single power-law spectrum. Although this is consistent with the observational result that the density of the ambient plasma is not high enough to stop high energy electrons, we need to study other events, especially intense events from which more accurate spectra can be derived, in order to confirm this result.

We present hard X-ray imaging observations of impulsive solar flares with Yohkoh HXT, focusing on the evolution of hard X-ray double footpoint sources seen in the energy range above 30 keV. In 7 out of the 14 events studied, the separation between the double sources increases (at the 3σ confidence level) as the flare progresses, with the double sources moving nearly anti-parallel to each other in most cases. Implications of these results to the global magnetic field structure responsible for solar flare energy release / particle acceleration are discussed.

New results concerning magnetic reconnection in the solar corona are reviewed. We apply the collisionless 3D reconnection theory — more exactly, the model of a high-temperature turbulent-current non-neutral current sheet — to the coronal conditions derived from the observations with the HXT and SXT onboard Yohkoh . New interpretations are discussed of the Yohkoh data on the site and mechanism of magnetic energy transformation into kinetic and thermal energies of superhot plasmas and accelerated high-energy particles. Open issues are the focus of our attention.

We analyze the footpoint separation d and flux asymmetry A of magnetically conjugate double footpoint sources in hard X-ray images from the Yohkoh Hard X-Ray Telescope (HXT). The data set of 54 solar flares includes all events simultaneously observed with the Compton Gamma Ray Observatory (CGRO) in high time resolution mode. From the CGRO data we deconvolved the direct-precipitation and trap-precipitation components previously (in Paper II). Using the combined measurements from CGRO and HXT, we develop an asymmetric trap model that allows us to quantify the relative fractions of four different electron components, i.e., the ratios of direct-precipitating (qP1, qP2) and trap-precipitating electrons (qT1, qT2) at both magnetically conjugate footpoints. We find mean ratios of qP1=0.14 ± 0.06, qP2=0.26 ± 0.10, and qT=qT1+qT2=0.60 ± 0.13. We assume an isotropic pitch-angle distribution at the acceleration site and double-sided trap precipitation (qT2/qT1=qP2/qP1) to determine the conjugate loss-cone angles (α1=42° ± 11° and α2=52° ± 10°) and magnetic mirror ratiosat both footpoints (R1=1.6,...,4.0 and R2=1.3,...,2.5). From the relative displacement of footpoint sources we also measure altitude differences of hard X-ray emission at different energies, which are found to decrease systematically with higher energies, with a statistical height difference of hLo-hM1=980 ± 250 km and hM1-hM2=310 ± 300 km between the three lower HXT energy channels (Lo, M1, M2).

We present an overview and instrumental details of the solar XUV Doppler Telescope (XDT) launched in January 1998 with the S520CN-22 sounding rocket of the Institute of Space and Astronautical Science. The XDT observes nearly single-temperature solar corona at 1.8 MK with angular resolution of ≈ 5′′ pixel size, together with the ability to detect the coronal velocity field with a full-Sun field of view. By use of normal incidence optics whose primary and secondary mirrors are coated with multilayer materials in two sectors, the XDT takes images of the Sun in a set of shorter and longer wavelength bands around the Fe xiv 211.3 A emission line. Summation of a pair of images in the two bands provides an image of the 1.8 MK-corona while the difference between the two provides velocity images of the Fe xiv-emitting plasma. A brief description on the observation sequence together with the flight result is also given.

Two subclasses of impulsive solar flares, observed with the Hard X-Ray Telescope (HXT) onboard Yohkoh, have been discovered by Sakao et al. The two subclasses can be characterized as more impulsive (MI) and less impulsive (LI) flares, the former having a shorter total duration of the impulsive phase in the hard X-ray emission than the latter. We assume that in both subclasses, the collisionless three-dimensional reconnection process occurs at the separator with a longitudinal magnetic field. The high-temperature turbulent-current sheet (HTTCS), located along the separator, generates accelerated particles and fast outflows of "superhot" (T ≥ 30 MK) plasma. Powerful anomalous heat-conductive fluxes along the reconnected field lines maintain a high temperature in the superhot plasma. The difference between the LI and MI flares presumably appears because the footpoint separation (the distance between two brightest hard X-ray sources) increases in time in the LI flares, but decreases in the MI flares. According to our model, in the LI flares the three-dimensional reconnection process accompanies an increase in the longitudinal magnetic field at the separator. In contrast, in the MI flares the reconnection proceeds with a decrease of the longitudinal field; hence, the reconnection rate is higher in the MI flares. Since reconnection in the MI flares proceeds with a decrease of the longitudinal field, the reconnected field lines become shorter in this process. As the reconnected lines become shorter, accelerated electron beams arrive at the upper chromosphere faster. So, in the MI flares chromospheric evaporation begins earlier than in the LI flares. The evaporation process driven by accelerated electron beams generates upflows of "warm" (T ≤ 10 MK) plasma that interacts with downflows of superhot plasma and can switch off the accumulation of superhot plasma in the MI flares during the impulsive phase. In the LI flares, however, an observable amount of superhot plasma is accumulated even during the impulsive phase. Moreover, since the cooling timescales increase with the length of the reconnected field lines, our argument for the association of superhot plasma with longer lines may remain valid to a reasonable extent even if the chromospheric evaporated plasma mixes with the reconnected outflow and superhot temperatures are reached in this mixture. Further analysis of the Yohkoh data obtained simultaneously with the Hard and Soft X-Ray Telescopes and the bent crystal spectrometer (BCS) is necessary to distinguish the superhot components of chromospheric and coronal origins in different classes of flares as well as at different phases of their development.

Imaging observations of solar flare hard X-ray sources with the Hard X-ray Telescope (HXT) aboard the Yohkoh satellite have revealed that hard X-ray emissions (greater than 30 ke V) originate most frequently from double sources. The double sources are located on both sides of the magnetic neutral line, suggesting that the bulk of hard X-rays is emitted from footpoints of flaring magnetic loops. We also found that hard X-rays from the double sources are emitted simultaneously within a fraction of second and that the weaker source tends to be located in the stronger magnetic field region, showing a softer spectrum. Physcial implications on the observed characteristics of the hard X-ray double sources are discussed.

Particle acceleration is intrinsic to the primary energy release in the impulsive phase of solar flares, and we cannot understand flares without understanding acceleration. New observations in soft and hard X-rays, γ-rays and coherent radio emissions are presented, suggesting flare fragmentation in time and space. X-ray and radio measurements exhibit at least five different time scales in flares. In addition, some new observations of delayed acceleration signatures are also presented. The theory of acceleration by parallel electric fields is used to model the spectral shape and evolution of hard X-rays. The possibility of the appearance of double layers is further investigated.

Yohkoh observations of an impulsive solar flare which occurred on 16 December, 1991 are presented. This flare was a GOES M2.7 class event with a simple morphology indicative of a single flaring loop. X-ray images were taken with the Hard X-ray Telescope (HXT) and soft X-ray spectra were obtained with the Bragg Crystal Spectrometer (BCS) on board the satellite. The spectrometer observations were made at high sensivity from the earliest stages of the flare, are continued throughout the rise and decay phases, and indicate extremely strong blueshifts, which account for the majority of emission in Caxix during the initial phase of the flare. The data are compared with observations from other space and ground-based instruments. A balance calculation is performed which indicates that the energy contained in non-thermal electrons is sufficient to explain the high temperature plasma which fills the loop. The cooling of this plasma by thermal conduction is independently verified in a manner which indicates that the loop filling factor is close to 100%. The production of ‘superhot’ plasma in impulsive events is shown to differ in detail from the morphology and mechanisms appropriate for more gradual events.

Ginga observations of the contact binary VW Cep are presented. The observed X-ray luminosity is 1.1×10 30 erg/s in the energy range of 2-10 keV, assuming a distance of 31 pc. No evidence for X-ray orbital modulation or for flare events was seen. The observed X-ray spectrum is very hard, and can be represented well either by a thermal bremsstrahlung model with a temperature of 11.2 keV or a power-law model with photon index of Γ = 1.90. These observational results are interpreted in terms of thermal emission from hot coronal plasma extending beyond the stellar size. However the observed upper limit on the iron K-line intensity is considerably below the theoretical prediction

Ginga observations of the old nova GK Persei in quiescence are reported, as well as a brief scanning observation during an outburst. The X-ray spectrum in quiescence is well fitted by thermal bremsstrahlung emission of very high temperature, plus an iron emission line. In contrast, the outburst spectrum is complex and comprises two continua with different column densities. The 351-s spin modulation of GK Per was clearly detected in the quiescence observation, which confirms the results of previous EXOSAT observations. The folded light curve shows two peaks that are not separated by 180° in phase, which is indeed quite different from the EXOSAT outburst data. It is, however, similar to the EXOSAT observation at a similar flux level

著者人数：12名, 資料番号: SA1001982000

Ginga observations of the X-ray binary pulsar GX301-2 are analysed for their temporal and spectral properties. The unambiguous detection of aperiodic intensity variations of 7-10 per cent rms relative amplitude over time-scales covering ∼16 to 0.1 s is reported. These variations are self-similar, being well fitted by a power law in power spectral density versus frequency space. The pulse period measured is 689.80 s, the shortest yet measured for this source. The fraction of X-rays which is pulsed is energy dependent, being greater at higher energies

著者人数：11名, Accepted: 1991-04-25, 資料番号: SA1001933000

著者人数：12名, 資料番号: SA1001977000

The formation of the slow solar wind has been debated for many years. In this Letter we show evidence of persistent outflow at the edges of an active region as measured by the EUV Imaging Spectrometer on board Hinode. The Doppler velocity ranged between 20 and 50 km s^-1 and was consistent with a steady flow seen in the X-Ray Telescope. The latter showed steady, pulsing outflowing material and some transverse motions of theloops. We analyze the magnetic field around the active region and produce a coronal magnetic field model. We determine from the latter that the outflow speeds adjusted for line-of-sight effects can reach over 100 km s^-1. We can interpret this outflow as expansion of loops that lie over the active region, which may either reconnect with neighboring large-scale loops or are likely to open to the interplanetary space. This material constitutes atleast part of the slow solar wind. Fil: Harra, L. K.. Mullard Space Science Laboratory; Reino Unido Fil: Sakao, T.. Institute of Space and Astronautical Science; Japón Fil: Mandrini, Cristina Hemilse. Consejo Nacional de Investigaciónes Científicas y Técnicas. Oficina de Coordinación Administrativa Ciudad Universitaria. Instituto de Astronomía y Física del Espacio. - Universidad de Buenos Aires. Facultad de Ciencias Exactas y Naturales. Instituto de Astronomía y Física del Espacio; Argentina Fil: Hara, H.. National Astronomical Observatory of Japan; Japón Fil: Imada, S.. National Astronomical Observatory of Japan; Japón Fil: Young, P. R.. Rutherford Appleton Laboratory; Reino Unido Fil: van Driel Gesztelyi, Lidia. Centre National de la Recherche Scientifique. Observatoire de Paris; Francia Fil: Baker, D.. Mullard Space Science Laboratory; Reino Unido

We present a detailed examination of strongly blueshifted emission lines observed with the EUV Imaging Spectrometer on board the {\it Hinode} satellite. We found two kinds of blueshifted phenomenon associated with the X3.4 flare that occurred on 2006 December 13. One was related to a plasmoid ejection seen in soft X-rays. It was very bright in all the lines used for the observations. The other was associated with the faint arc-shaped ejection seen in soft X-rays. The soft X-ray ejection is thought to be an MHD fast-mode shock wave. This is therefore the first spectroscopic observation of an MHD fast-mode shock wave associated with a flare., Comment: 18 pages, 1 table, 6 figures. ApJ, accepted

著者人数：29名, Accepted: 2007-03-08, 資料番号: SA1000202000

ERRATUM: “OUTFLOWS AT THE EDGES OF ACTIVE REGIONS: CONTRIBUTION TO SOLAR WIND FORMATION?”(ApJ, 676, L147 [2008])L. K. Harra, T. Sakao, C. H. Mandrini, H. Hara, S. Imada, P. R. Young, L. van Driel–Gesztelyi, and D. BakerThrough an oversight, an incorrect figure was submitted for publication. Here is the correct Figure 3.

We analyze simultaneous H(alpha) images and spectra (from Mees Solar Observatory), and soft and hard X-ray images and spectra (from YOHKOH) during the early phase of an X1.5/3B flare. We investigate the morphological relationship between chromospheric downflows, coronal upflows, and particle precipitation sites, and the energetic relationship between conductive heating, nonthermal particle heating, and the chromospheric response. We find that the observations consistently fit the chromospheric evaporation model. In particular, we demonstrate that the observed upflowing coronal and downflowing chromospheric plasma components originate in the same locations, and we show that our unique set of optical and X-ray observations can clearly distinguish between conductively driven and electron beam driven evaporation.

The Yohkoh soft X-ray telescope has observed impulsive, thermal, soft X-ray emission at the footpoints of magnetic loops during solar flares. The soft X-ray (thermal) time profiles at the footpoints closely match the hard X-ray (nonthermal) time profiles, directly demonstrating the heating of the lower solar atmosphere on short timescales during the interval of nonthermal energy release. This phenomenon is the rule, rather than the exception, occurring in the majority of flares that we have examined with the Yohkoh data. We illustrate the impulsive behavior with data from the major flare of 1992 January 26. For this flare, the soft X-ray peak times matched the hard X-ray peak times within the time resolution of the soft X-ray measurements (about 10 s), and the soft and hard X-ray locations match within the resolution of the hard X-ray imager. The impulsive soft X-ray emission clearly has a thermal spectral signature, but not at the high temperature of a 'superhot' source. We conclude that the impulsive soft X-ray emission comes from material heated by precipitating electrons at loop footpoints and evaporating from the deeper atmosphere into the flaring flux tube.

A remarkable absorption feature at 28.5 keV, attributable to electron cyclotron resonance, has been discovered in the 1.9-60-keV X-ray spectrum of the recurrent transient X-ray pulsar X0331 + 53. The observed resonance energy implies a neutron star surface magnetic field of 2.5(1 + z) x 10 to the 12th G, where z is the gravitational redshift. The detection was made with the Ginga observatory in October 1989, during an outburst of this transient with a flux level of about 0.3 Crab. The feature is very deep and has been resolved with excellent statistics. This is the fourth unambiguous detection of cyclotron resonant scattering features from X-ray pulsars, suggesting that these features are a common phenomenon among these objects. An empirical relation found between the cyclotron resonance energy and the spectral cutoff energy suggests that the magnetic field strengths of the known X-ray pulsars are clustered in a range (1-4) x 10 to the 12th G. 30 refs.

A cyclotron absorption line near 20 keV has been found in the spectrum of the massive eclipsing binary X-ray pulsar 4U 1538 - 52 in observations with the Ginga observatory. The line is detected throughout the 529 s pulse cycle with a variable equivalent width that has its maximum value during the smaller peak of the two-peak pulse profile. It is found that the profile of the pulse and the phase-dependence of the cyclotron line can be explained qualitatively by a pulsar model based on recent theoretical results on the properties of pencil beams emitted by accretion-heated slabs of magnetized plasma at the magnetic poles of a neutron star. The indicated field at the surface of the neutron star is 1.7 (1 + z) x 10 to the 12th G, where z is the gravitational redshift.

We obtained temperature structures in faint coronal features above and near the solar limb with the X-Ray Telescope aboard the Hinode satellite by accurately correcting the scattered X-rays from surrounding bright regions with occulted images during the solar eclipses. Our analysis yields a polar coronal hole temperature of about 1.0 MK and an emission measure in the range of 10 25:5 –10 26:0 cm � 5 . In addition, our methods allow us to measure the temperature and emission measure of two distinct quiet-Sun structures: radial (plume-like) structures near the boundary of the coronal-hole and diffuse quiet Sun regions at mid-latitudes. The radial structures appear to have increasing temperature with height during the first 100 Mm, and constant temperatures above 100 Mm. For the diffuse quiet-Sun region the temperatures are the highest just above the limb, and appear to decrease with height. These differences may be due to different magnetic configurations.

著者人数：14名, Accepted: 2007-08-26, 資料番号: SA1000271000