共查询到20条相似文献，搜索用时 15 毫秒
1.
John M. Davis 《Solar physics》1985,95(1):73-82
To study the formation and development of coronal holes, their association with X-ray bright points has been investigated. The areal density of X-ray bright points was measured within the boundaries of coronal holes and was found to increase linearly with time for each of the three, long-lived, equatorial coronal holes of the Skylab era. Analysis of the data shows that the effect is not the result of global changes in bright point number and is therefore a property of the restricted longitude region which contains the coronal hole. The bright point density at the time of the hole's formation was also measured and, although the result is more uncertain, was found to be similar to the bright point number over the solar surface. No association was found between bright points and the rate of change of coronal hole area. 相似文献
2.
X-ray images obtained during two rocket flights near the maximum of sunspot cycle 21 now allow the study of the variation of X-ray bright point number over an eleven-year period covering the maxima of the last two cycles. The new data are consistent with the earlier conclusion that the temporal variation of bright point and sunspot number are out of phase. The quantities are related through a power law with a negative exponent of 2/3. 相似文献
3.
We describe adapting a method that is used to find point sources in Chandra X-ray telescope data for use in finding solar X-ray bright points. The algorithm allows selected pixels to be excluded from the source-finding, thus excluding saturated pixels (from flares and/or active regions). For Chandra data the noise is determined by photon-counting statistics, whereas solar telescopes typically integrate a flux. Thus, the calculated signal-to-noise ratio is incorrect, but we find that we can scale the number to get reasonable results. We compare our source-finding to previous Yohkoh results and find a similar number of bright points. Finally, we analyze three sets of data from Hinode, representing different parts of the decline to minimum of the solar cycle. Although these preliminary results are based on a small sample, we see no dependence on the solar cycle. 相似文献
4.
《New Astronomy Reviews》2000,44(7-9):555-557
We present some early results on AGN from the Chandra X-ray Observatory, highlighting high resolution spectroscopy using the High Energy Transmission Grating Spectrometer (HETGS). The quasar PKS 0637–752 was found to have a very bright X-ray jet whose shape is remarkably similar to that of the radio jet on a size scale of 100 kpc, but the X-ray emission is still inexplicably bright. Two BL Lac objects, PKS 2155–304 and Mrk 421, observed with the spectrometer were found to have no strong absorption or emission features. Other radio loud AGN observed with the HETGS show simple power law spectra without obvious features. 相似文献
5.
X-ray bright points are small dynamic loop structures that are observed all over the solar corona. The high spatial and temporal
resolution of the TRACE instrument allows bright points to be studied in much greater detail than previously possible. This
paper focuses on a specific bright point which occurred for about 20 hours on 13–14 June 1998 and examines its dynamic structure
in detail. This example suggests that the mechanisms that cause bright points to form and evolve are more complex than previously
thought. In this case, reconnection probably plays a major part during the formation and brightening of the loop structure.
However, later on the foot points rotate injecting twist into the bright point which may cause an instability to occur with
dynamic results.
Supplementary material to this paper is available in electronic form at http://dx.doi.org/10.1023/A:1017907406350 相似文献
6.
Our investigation has been carried using the instruments onboard the Solar Dynamics Observatory (SDO) providing a high resolution of images (AIA photographs and HMI magnetograms). We have investigated the structure and magnetic evolution of several coronal bright points and small scale N-S polarity magnetic fluxes closely associated with them. We also compare the evolution of the magnetic polarities of elementary isolated sources of positive and negative fluxes (magnetic bipoles) and coronal bright points. Tiny (“elementary”) coronal bright points have been detected. A standard coronal bright point is shown to be a group of “elementary” coronal bright points that flare up sequentially. Our investigation shows that a change in the magnetic fluxes of opposite polarities is observed before the flare of a coronal bright point. We show that not all cases of the formation of coronal bright points are described by the magnetic reconnection model. This result has not been considered previously and has not been pointed out by other authors. 相似文献
7.
J. T. Nolte J. M. Davis M. Gerassimenko A. S. Krieger C. V. Solodyna L. Golub 《Solar physics》1978,60(1):143-153
We examine the relationship between coronal hole evolution and solar active regions during the Skylab period. We find a tendency for holes to grow or remain stable when the activity nearby, seen as calcium plages and bright regions in X-rays, is predominantly large, long-lived regions. This is consistent with results of previous studies, using somewhat different methods. We also find that there is a significantly higher number of small, short-lived active regions, as indicated by X-ray bright points, in the vicinity of decaying holes than there is near other holes. We interpret this to mean that holes disappear at least in part because they become filled with many small scale, magnetically closed, X-ray emitting features. This interpretation, together with the previously reported observation that the number of X-ray bright points was much larger near solar minimum than it was during the Skylab period, provides a possible explanation for the disappearance of the large, near-equatorial coronal holes at the time of solar minimum. 相似文献
8.
Using near-simultaneous full disk solar X-ray images and Hei 10830 spectroheliograms from three rocket flights, we compare dark points identified on the Hei maps with X-ray bright points identified on the X-ray images. We find that for the largest and most obvious features there is a strong correlation: most Hei dark points correspond to X-ray bright points. However, about two-thirds of the X-ray bright points were not identified on the basis of the helium data alone. Once an X-ray feature is identified it is almost always possible to find an underlying dark patch of enhanced Hei absorption which, however, would not a priori have been selected as a dark point. Therefore, the Hei dark points, using current selection criteria, cannot be used as a one-to-one proxy for the X-ray data. Hei dark points do, however, identify the locations of the stronger X-ray bright points.Visitor, National Solar Observatory. National Optical Astronomy Observatories operated by the Association of Universities for Research in Astronomy, Inc. under contract with the National Science Foundation. 相似文献
9.
A recent discovery from the Big Bear Solar Observatory has linked the cancellation of opposite polarity magnetic fragments in the photosphere (i.e., so-called cancelling magnetic features) to X-ray bright points and has stimulated the setting up of a converging flux model for the process. Cancelling magnetic features can occur between magnetic fragments of differing strengths in many different situations. Here, therefore, we model two opposite polarity fragments of different strengths in the photosphere by two unequal sources in an overlying uniform field. Initially in thepre-interaction phase these sources are assumed to be unconnected, but as they move closer together theinteraction phase starts with an X-type neutral point forming, initially on the photosphere, then rising up into the chromosphere and corona before lowering back down to the photosphere. Thecapture phase then follows with the sources fully connected as they move together. Finally, after they come in to contact, during thecancellation phase the weaker source is cancelled by part of the stronger source. The height of the X-type neutral point varies with the separation of the sources and the ratio of the source strengths, as do the positions of the neutral points before connection and after complete reconnection of the two sources. The neutral point is the location of magnetic reconnection and therefore energy release which is believed to power the X-ray bright point in the corona. By using a current sheet approximation, where it is assumed no reconnection takes place as the two sources move together, the total amount of energy released during reconnection may be estimated. The typical total free magnetic energy is found to be of the order of 1020–1021 J, which is as required for an X-ray bright point. It is also found that, as the ratio of the source strengths increases, the height of the X-type neutral point decreases, as do the total energy released, and the lifetime of the bright point. 相似文献
10.
We present examples of X-ray jets, observed by the Soft X-ray Telescope on board Yohkoh, which followed trajectories of transequatorial interconnecting loops (TILs). All these TILs were preexisting, seen some
time before, but were mostly invisible at the time of the onset of the jet which often made them bright along their total
length. With few exceptions, these TIL-associated jets have properties very similar to other jets ejected inside active regions
or along open field lines (footpoints in X-ray bright points, recurrence, strong collimation, average speed close to 350 km s−1), but may reach larger lengths, in our examples up to 450 000 km. Exceptions are one jet that moved slower and one that had
no brightened area at its supposed source region at the time of its origin (an X-ray bright point appeared there only 3 hours
later). It appears that quite a high number of X-ray jets may be of this TIL-associated kind.
Supplementary material to this paper is available in electronic form at http://dx.doi.org/10.1023/A:1014963812437 相似文献
11.
Ian R. Stevens David K. Strickland Karen A. Wills 《Monthly notices of the Royal Astronomical Society》1999,308(3):L23-L27
We investigate the X-ray emission from the central regions of the prototypical starburst galaxy M82. Previous observations have shown a bright central X-ray point source, with suggestions as to its nature including a low-luminosity active galactic nucleus or an X-ray binary. A new analysis of ROSAT HRI observations finds four X-ray point sources in the central kiloparsec of M82, and we identify radio counterparts for the two brightest X-ray sources. The counterparts are probably young radio supernovae (SNe) and are amongst the most luminous and youthful SNe in M82. We therefore suggest that we are seeing X-ray emission from young SNe in M82, and in particular that the brightest X-ray source is associated with the radio source 41.95+57.5. We discuss the implications of these observations for the evolution of X-ray-luminous SNe. 相似文献
12.
分析１９８５年ＥＸＯＳＡＴ卫星对银河核球Ｘ射线源ＧＸ９＋１的观测数据，发现该源存在几百秒量级的振荡现象，这一结果有助于了解小质量Ｘ射线双星Ｇｘ９＋１的吸积特性和轨道运动。 相似文献
13.
We use MDI magnetic field observations and the theory of reconnection through a separator to constrain a numerical simulation
of an X-ray bright point observed in EUV by TRACE. A gasdynamic model is employed to describe the corona and transition region
in the bright point loop. Nonlocal effects such as opacity and ambipolar diffusion are important to the transition region;
these effects are approximated locally by modification of the radiative loss and thermal conduction. A straightforward comparison
of measured light curves versus those generated by the simulation shows that the reconnection model is unable to account for
the observations.
Supplementary material to this paper is available in electronic form at http://dx.doi.org/10.1023/A:1005205807984 相似文献
14.
H. Arp 《Astrophysics and Space Science》1998,262(3):337-361
Observations of three different sized regions centered on the optical jet spiral, NGC 1097 have been made with ROSAT. The PSPC observations show a striking excess of bright and medium flux X-ray sources around this hot spot nucleus, Seyfert 1 galaxy. The brightest of these sources are catalogued quasars which suggests the fainter X-ray sources are predominantly quasars also. If so, of the order of at least 10 and possibly considerably more X-ray quasars appear to be associated with NGC 1097 within a radius of 20. There is a marked segregation, with bright X-ray sources on the side of the bright optical jets and weak X-ray sources on the side of the fainter optical jets. Some, but not all, of this asymmetry could be accounted for by absorption in the plane of the spiral being tilted towards us on the weak source side. Both optical and X-ray evidence point to strong absorption in the disk of NGC 1097 which reaches far beyond the optical limits. High resolution imaging (HRI) of regions closer to NGC 1097 reveal some fainter pairs and lines of X-ray sources aligned across the nucleus near the cones defined by the optical jets. Filaments and patches of ultraviolet emission (1500–1700Å) appear to fill in the region between the strong optical jets in the direction of the bright X-ray quasars, suggesting physical association of the ultraviolet emission with the quasars and the galaxy. Finally, ROSAT SURVEY observations have been examined over a 4 × 4 degree field centered on NGC 1097. A line of X-ray sources going through the galaxy in the direction of the strongest optical jet includes a strong X-ray quasar with its X-ray isophotes extended toward NGC 1097. In approximately the opposite direction, 1.9 degrees distant, is a strong X-ray source (.5cts s-1) which is here identified with a 16.5 mag BL Lac object. 相似文献
15.
Due to the broad wings of the point spread function of the Wolter telescopes used in the Skylab mission for taking X-ray pictures of the solar corona, the images are blurred around bright emission regions. As a result, the maps of temperature and emission measure are distorted. A procedure for the iterative deconvolution of X-ray pictures is given and applied to the images taken by the AS & E Inc. and the Aerospace Corporation instruments. 相似文献
16.
Chandreyee Sengupta † Ramesh Balasubramanyam K. S. Dwarakanath 《Monthly notices of the Royal Astronomical Society》2007,378(1):137-147
Environment plays an important role in the evolution of the gas contents of galaxies. Gas deficiency of cluster spirals and the role of the hot intracluster medium in stripping gas from these galaxies is a well-studied subject. Loose groups with diffuse X-ray emission from the intragroup medium (IGM) offer an intermediate environment between clusters and groups without a hot IGM. These X-ray bright groups have smaller velocity dispersion and lower temperature than clusters, but higher IGM density than loose groups without diffuse X-ray emission. A single-dish comparative study of loose groups with and without diffuse X-ray emission from the IGM, showed that the galaxies in X-ray bright groups have lost more gas on average than the galaxies in non X-ray bright groups. In this paper we present GMRT H i observations of 13 galaxies from four X-ray bright groups: NGC 5044, 720, 1550 and IC1459. The aim of this work is to study the morphology of H i in these galaxies and to see if the hot IGM has in any way affected their H i content or distribution. In addition to disturbed H i morphology, we find that most galaxies have shrunken H i discs compared to the field spirals. This indicates that IGM-assisted stripping processes like ram pressure may have stripped gas from the outer edges of the galaxies. 相似文献
17.
Jing Tang Wen-Fei Yu Zhen Yan Key Laboratory for Research in Galaxies Cosmology Shanghai Astronomical Observatory Shanghai China 《中国天文和天体物理学报》2011,(4)
We have studied X-ray spectral state transitions that can be seen in the longterm monitoring light curves of bright X-ray binaries from the All-Sky Monitor (ASM) onboard the Rossi X-ray Timing Explorer (RXTE) and the Burst Alert Telescope (BAT) onboard Swift during a period of five years from 2005 to 2010.We have applied a program to automatically identify the hard-to-soft (H-S) spectral state transitions in the bright X-ray binaries monitored by the ASM and the BAT.In total,we identified 128 hard-to-soft t... 相似文献
18.
Imaging microwave observations of an eruptive, partially occulted solar flare on 18 April 2001 suggest that the global structure
of the event can be described by the helical kink instability of a twisted magnetic flux rope. This model is suggested by
the inverse gamma shape of the source exhibiting crossing legs of a rising flux loop and by evidence that the legs interact
at or near the crossing point. The interaction is reflected by the location of peak brightness near the crossing point and
by the formation of superimposed compact nonthermal sources most likely at or near the crossing point. These sources propagate
upward along both legs, merge into a single, bright source at the top of the structure, and continue to rise at a velocity
>1000 km s−1. The compact sources trap accelerated electrons which radiate in the radio and hard X-ray ranges. This suggests that they
are plasmoids, although their internal structure is not revealed by the data. They exhibit variations of the radio brightness
temperature at a characteristic time scale of ∼ 40 s, anti-correlated to their area, which also support their interpretation
as plasmoids. Their propagation path differs from the standard scenario of plasmoid formation and propagation in the flare
current sheet, suggesting the helical current sheet formed by the instability instead. 相似文献
19.
Center-limb observations of line-center intensity and velocity fluctuations in the Magnesium b lines are described. Autocorrelation and power spectral analyses indicate small scale brightness structures having periodicities of 3000 km and 8000 km and large scale structures of 22000 km. Corresponding velocity structures are 6000 km and 30000 km.The relative rms fluctuation amplitude for the small scale bright features is found to be of order 12% and for the large scale features 8%. The variation of these rms values with heliocentric angle is also shown.At disk center some weak correlation is found between bright features and downward velocities in the large scale structures. Towards the limb there is a strong correlation in all three lines between line of sight motions and bright features. This indicates that the large scale bright features are closely associated with the supergranule motions.By inspecting the actual brightness and velocity fluctuation tracings it can be seen that, in some regions, the small scale structures show a significant negative correlation over a range of about 25000 km. Beyond this characteristic length, however, the correlation may decrease abruptly or even become positive for a similar distance. There is some evidence which suggests that this behaviour may also be related to the supergranule motions. 相似文献
20.
研究亮暴和暗暴的X射线余辉,发现它们的X射线和γ流量的分布基本上相同。即:从统计学的角度上讲,亮暴和暗暴没有本质不同,它们的中心机制应该是相同的,暗暴的形成应该是由环境原因引起的。 相似文献