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1.
A Chandra X-ray observation of the globular cluster Terzan 1   总被引：1，自引：0，他引：1  
We present a ∼19-ks Chandra Advanced CCD Imaging Spectrometer (ACIS)-S observation of the globular cluster Terzan 1. 14 sources are detected within 1.4 arcmin of the cluster centre with two of these sources predicted to be not associated with the cluster (background active galactic nuclei or foreground objects). The neutron star X-ray transient, X1732−304, has previously been observed in outburst within this globular cluster with the outburst seen to last for at least 12 yr. Here, we find four sources that are consistent with the ROSAT position for this transient, but none of the sources are fully consistent with the position of a radio source detected with the Very Large Array that is likely associated with the transient. The most likely candidate for the quiescent counterpart of the transient has a relatively soft spectrum and an unabsorbed 0.5–10 keV luminosity of  2.6 × 1032 erg s−1  , quite typical of other quiescent neutron stars. Assuming standard core cooling, from the quiescent flux of this source we predict long (>400 yr) quiescent episodes to allow the neutron star to cool. Alternatively, enhanced core cooling processes are needed to cool down the core. However, if we do not detect the quiescent counterpart of the transient this gives an unabsorbed 0.5–10 keV luminosity upper limit of  8 × 1031 erg s−1  . We also discuss other X-ray sources within the globular cluster. From the estimated stellar encounter rate of this cluster we find that the number of sources we detect is significantly higher than expected by the relationship of Pooley et al.  相似文献   

2.
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3.
A model of filament formation based on the condensation of coronal arches is described. The condensation results from initiating the radiative instability within an arch by superimposing a transient energy supply upon the steady state heating mechanism. The transient energy supply increases the density within the arch so that when it is removed the radiative losses are sufficient to lead to cooling below the minimum in the power loss curve.Times from the initial formation of the condensation to its temperature stabilization as a cool filament have been calculated for various initial conditions. They lie in the range 104 to 105 s with the majority of the time spent above a temperature of 1 × 106 K.Under the assumption that the condensation of a single arch forms an element of the filament, a complete filament requires the condensation of an arcade of loops. Using experimentally derived parameters, filament densities of 1011 to 1012 cm–3 can be obtained.  相似文献   

4.
We suggest that an extreme Kerr black hole with a mass ∼106 M⊙, a dimensionless angular momentum     and a marginally stable orbital radius     located in a normal galaxy may produce a γ -ray burst (GRB) by capturing and disrupting a star. During the capture period, a transient accretion disc is formed and a strong transient magnetic field ∼     lasting for     may be produced at the inner boundary of the accretion disc. A large amount of rotational energy of the black hole is extracted and released in an ultrarelativistic jet with a bulk Lorentz factor Γ larger than 103 via the Blandford–Znajek process. The relativistic jet energy can be converted into γ -radiation via an internal shock mechanism. The GRB duration should be the same as the lifetime of the strong transient magnetic field. The maximum number of sub-bursts is estimated to be     because the disc material is likely to break into pieces with a size about the thickness of the disc h at the cusp     The shortest risetime of the burst estimated from this model is ∼     The model GRB density rate is also estimated.  相似文献   

5.
Pneuman  G. W. 《Solar physics》1984,94(2):387-411
Adopting the point of view that a coronal transient is a defined magnetic structure, it must be diamagnetic with respect to the external ambient magnetic field, i.e., the external field lines cannot penetrate the structure. If this is so, an integral approach involving only external forces can be very useful for studying the conditions for acceleration and large-scale dynamical behavior of the transient.After a discussion of a suggested transient configuration based upon observations of prominences, flare loops, and transient - filament relative orientations observed by Trottet and MacQueen (1980), we demonstrate the diamagnetic approach to this problem through a particularly simplified model. Necessary conditions for upward acceleration of the transient are discussed in some detail. One such plausible initiation mechanism is shown to be a constriction of the structure near its base by the external forces. This mechanism not only can provide the upward acceleration for the transient but is also compatible with the observation of hot rising flare loops during two-ribbon flare which show evidence for magnetic reconnection.We have studied the equilibrium conditions and dynamical behavior of the transient using this mechanism for two limiting cases - that in which the gas pressure in the structure dominates over the magnetic pressure and that in which the magnetic pressure dominates. For both cases, the required equilibrium conditions are compatible with observed coronal parameters. The dynamical behavior upon inward constriction, however, resembles the observed characteristics for transients best for the magnetically dominated case. For example, in the pressure-dominated case, the required temperatures for acceleration appear somewhat high being in excess of about 1.9 × 106 K. If, in addition, the internal temperature declines adiabatically during the outward motion, the structure does not reach inifinity unless its initial temperature exceeds about 3 × 106 K but stops a some radial distance, returns to the Sun only to be accelerated outward again in the same fashion. The rather stringent requirements on internal temperature for the pressure-dominated case in addition to the expectation that pressure-dominated transients should evolve into a thin pencil shape instead of maintaining an approximately self-similar profile as observed are strong arguments in favor of the magnetically dominated case.Based upon the above results, we suggest that the reconnection process evidenced in two-ribbon flares may not necessarily be the result of the relaxation of a locally open field configuration produced by the transient as described by Kopp and Pneuman (1976) but, instead, that the acceleration of the transient and the two-ribbon flare both may be produced by a common force, namely that provided by the constricting effect of the external magnetic field displaced by the presence of the structure.The National Center for Atmospheric Research is sponsored by the National Science Foundation.  相似文献   

6.
Every two-ribbon flare observed during the Skylab period produced an observable coronal transient, provided the flare occurred close enough to the limb. The model presented here treats these two events as a combined process. Transients that occur without flares are believed to involve magnetic fields that are too weak to produce significant chromospheric emission. Adopting the hypothesis that the rising flare loop systems observed during two-ribbon flares are exhibiting magnetic reconnection, a model of a coronal transient is proposed which incorporates this reconnection process as the driving force. When two oppositely directed field lines reconnect a lower loop is created rooted to the solar surface (the flare loop) and an upper disconnected loop is produced which is free to rise. The magnetic flux of these upper loops is proposed as the driver for the transient. The force is produced by the increase in magnetic pressure under the filament and transient.A quantitative model is developed which treats the transient configuration in terms of four distinct parts- the transient itself with its magnetic field and material, the region just below the transient but above the filament, the filament with its magnetic field, and the reconnected flux beneath the filament. Two cases are considered - one in which all the prominence material rises with the transient and one in which the material is allowed to fall out of the transient. The rate of rise of the neutral line during the reconnection process is taken from the observations of the rising X-ray flare loop system during the 29 July, 1973 flare. The MHD equations for the system are reduced to four non-linear ordinary coupled differential equations which are solved using parameters believed to be realistic for solar conditions. The calculated velocity profiles, widths, etc., agree quite well with the observed properties of coronal transients as seen in white light. Since major flares are usually associated with a filament eruption about 10–15 min before the flare and since this model associates the transient with the filament eruption, we suspect that the transient is actually initiated some time before the actual flare itself.The National Center for Atmospheric Research is sponsored by the National Science Foundation.  相似文献   

7.
We discuss the detection and evolution of a complex series of transient and quasi-static solar-wind structures in the days following the well-known comet 2P/Encke tail disconnection event in April 2007. The evolution of transient solar-wind structures ranging in size from <105 km to >106 km was characterised using one-minute time resolution observation of Interplanetary Scintillation (IPS) made using the European Incoherent SCATter (EISCAT) radar system. Simultaneously, the global structure and evolution of these features was characterised by the Heliospheric Imagers (HI) on the Solar TERrestrial RElations Observatory (STEREO) spacecraft, placing the IPS observations in context. Of particular interest was the observation of one transient in the slow wind, apparently being swept up and entrained by a Stream Interaction Region (SIR). The SIR itself was later detected in-situ at Venus by the Analyser of Space Plasma and Energetic Atoms (ASPERA-4) instrument on the Venus Express (VEX) spacecraft. The availability of such diverse data sources over a range of different time resolutions enables us to develop a global picture of these complex events that would not have been possible if these instruments were used in isolation. We suggest that the range of solar-wind transients discussed here may be the interplanetary counterparts of transient structures previously reported from coronagraph observations and are likely to correspond to transient magnetic structures reported in in-situ measurements in interplanetary space. The results reported here also provide the first indication of heliocentric distances at which transients become entrained.  相似文献   

8.
Spectral calibration of scanning sky monitor on ASTROSAT   总被引：1，自引：0，他引：1  
Scanning Sky Monitor (SSM) on-board ASTROSAT is an X-ray detector in the energy range 2–10 keV to monitor the sky for transient X-ray sources. The science objective of SSM is to detect and locate these transient X-ray sources. We discuss here in this paper, the spectral calibration of SSM along with on-board calibration plans using the X-ray flux from the Crab nebula. Spectral response for SSM is derived using a routine in ftools and the inputs for deriving the response are got from the results of the experiments done on the qualification model for SSM.  相似文献   

9.
We report the result of an XMM–Newton observation of the black hole X-ray transient XTE J1650–500 in quiescence. The source was not detected, and we set upper limits on the 0.5–10 keV luminosity of  0.9–1.0 × 1031 erg s−1  (for a newly derived distance of 2.6 kpc). These limits are in line with the quiescent luminosities of black hole X-ray binaries with similar orbital periods (∼7–8 h).  相似文献   

10.
Impact structures in the crystalline rocks of the Canadian Shield range over two orders of magnitude in size and display morphologies recognized elsewhere in the solar system. This contribution draws upon new examinations of drill core from Canadian craters to reaffirm some relationships, modify others, and refine the transitions from simple to complex with central peak to peak‐ring structures. These include recognizing the hyperbolic form of transient craters, sharpening the allochthon–parautochthon distinction, and proposing new formulae for key relationships. It emphasizes the role of dynamic tensile strength and the attenuation of tensile rarefaction waves in determining the size of both transient and final crater dimensions. On Earth, depth (d) to diameter (D) ratios are not invariant at about 1:10 but change smoothly with size from 1:3 at Brent through 1:5 to 1:10 in the largest; that is, d = 0.4 D0.75. In craters in crystalline rocks, the central peak grows at about uplift = 0.175 D until, at D about 28 km, the uplift rises above the original surface then collapses to form a peak‐ring structure. These relationships demonstrate the dominant role of gravity in attenuating tensile rarefaction waves and controlling transient crater depth and overall size relative to the volume shocked.  相似文献   

11.
A large area (5×1010km2) of a coronal hole disappeared in concert with a transient brightening of a nearby high-latitude coronal arcade in the northern hemisphere on 15 May 1992. This coronal-hole disappearance took place in a time scale of half a day. It is suggested that the large-scale and quick change in coronal-hole geometry induced the eruption of originally closed coronal magnetic structure of the high-latitude arcade. An associated solar wind disturbance with the plasma speed of >700 km/sec was observed by IPS, and geomagnetic sudden commencement was reported on 18 May 1992.  相似文献   

12.
The Faraday rotation of a radio source (Pioneer 6) occulted by the solar corona has been measured by Levy et al. (1969). During the course of these measurements, three large-scale transient phenomena were observed. These events were preceded by subflares and class 1 flares. These transient events are interpreted as evidence for a coronal magnetic bottle at 10 R ⊙. The velocity of propagation for the disturbance is set at 200 km/sec; the dimension of the region, 10 R ⊙; field strength at 10 R ⊙, 0.02 G; particle density, 2.0 × 104/cm3; Alfvén speed, 320 km/sec. From the nature of the observations and the lack of related effects from similar flares on the interplanetary sector pattern observed at 1 AU, it is suggested that such coronal magnetic bottles expand to perhaps 10–30 R ⊙ and then contract to a few solar radii. Such a phenomena is evidence for an expansion of the corona with a sub-Alfvénic velocity. It is further suggested that such magnetic bottles may be important in the storage and diffusion of solar generated cosmic ray particles. NAS-NRC Postdoctoral Resident Research Associate.  相似文献   

13.
R. R. Fisher 《Solar physics》1977,55(1):135-141
On 20 April 1976 a coronal emission line transient was observed on the west limb of the Sun using a 5303 Fexiv detection system and the Sacramento Peak Observatory's 40 cm coronagraph. The transient as observed at a single sample point, and the time scale for this event was found to be about 40 min. Limb scans before and after the event are used to estimate the amount of coronal mass involved in this relatively slow event. A depletion of the inner corona of 4.4 × 1038 electrons (8.8 × 1014 G) is inferred by differencing pre- and post-event model electron density distributions.The National Center for Atmospheric Research is sponsored by the National Science Foundation.  相似文献   

14.
Many coronal transient exhibit a circular aspect, which has been interpreted up to now as a loop structure. From polarization measurements of the 10 August, 1973 transient observed by the ATM coronagraph, which allows the location of material away from the plane of the sky, we show that this particular transient is more likely to be a 3-dimensional, bubble-shaped structure, than a loop. The radial component of the speed is evaluated. A thin streamer close to the transient is displaced by its passage, both in the plane of the sky and in the direction perpendicular to it.  相似文献   

15.
The coronal transient event of 20–21 November is unusual in that its appearance is distinctly non-loop-like; rather, the transient resembles a confined ray or fan-like volume. Studies of the distribution of the coronal material with time indicate that this is a mass ejection event, involving about 1 × 1015 g of material from the lower corona. Analysis of the polarization signal of the event suggests that the event is associated with chromospheric activity in a region near longitude E68. The observed properties (distributions in brightness and polarization) of the transient are compared with the properties of a well-studied event of typical loop-like appearance, but rotated to simulate an edge-on appearance; the differences suggest that the 20–21 November event is not such an edge-on, loop-like transient, but rather is most simply described as an axisymmetric-cylindrical or conical volume, the boundaries of which remain constant over the events' lifetime. On this basis, the variation of the transient spatial density with height and the variation of density with time can be specified rather more certainly than for previously-studied coronal mass ejection events. Densities are found to range from 3 × 10–16 g cm–3 at 2.1 R heliocentric height early in the event to 1 × 10–18 g cm–3 at 4.0 R late in the event. Typical temporal variations of the ejected material (at a given heliocentric height) are found to be on the order of 10–18 g cm–3 s–1. The mass and momentum balance in the event have been estimated from the observed parameters, employing a multiparameter approach. We find that a model with modest mass flux typified by material speed u 0 50 km s–1 and a near balance between the event's pressure gradient force and gravity — with possibly a small hydromagnetic wave contribution to the total pressure — is consistent with the observations. The kinetic energy of the event, determined from the motion of the center of mass of the ejected material, is only about 1026 ergs, and thus is the smallest for any solar mass ejection studied to date.The National Center for Atmospheric Research is sponsored by the National Science Foundation.  相似文献   

16.
Multi-telescope observations of the coronal transient of 15–16 April, 1980 provide simultaneous data from the Solar Maximum Mission Coronagraph/Polarimeter, the Solwind Coronagraph, and the new Emission Line Coronagraph of the Sacramento Peak Observatory. An eruptive prominence-associated white light transient is for the first time seen as an unusual wave or brightening in Fe x gl6374 (but not in Fe xiv gl5303). Several interpretations of this fleeting enhancement are offered.The prominence shows a slowly increasing acceleration which peaks at the time of the Fe event. The white light loop transient surrounding the prominence expands at a well-documented constant speed to 10R , with an extrapolated start time at zero height coincident with the surface activity.This loop transient exemplifies those seen above 1.7R in that leading the disturbance is a bright (N e-enhanced) loop rather than dark. This is consistent with a report of the behavior of another eruptive event observed by Fisher and Poland (1981) which began as a density depletion in the lower corona, with a bright loop forming at greater altitudes. The top of the bright loop ultimately fades in the outer corona while slow radial growth continues in the legs.The National Center for Atmospheric Research is sponsored by the National Science Foundation.  相似文献   

17.
Wu  Chin-Chun  Dryer  Murray 《Solar physics》1997,173(2):391-408
A fully three-dimensional (3D), time-dependent, MHD interplanetary model has been used, for the first time, to study the relationship between one form of solar activity and transient variations of the north–south component, Bz, of the interplanetary magnetic field (IMF) at 1 AU during the active period of a representative solar cycle. Four cases of initial steady-state solar wind conditions, with different tilt angles of the heliospheric current sheet/plasma sheet (HCS/HPS) which is known to be inclined at solar maximum, are used to study the relationship between the location of solar activity and transient variations of the north–south IMF Bz component at 1 AU. We simulated the initialization of the disturbance as a density pulse at different locations near the solar surface for each case of initial steady-state condition and observed the simulated IMF evolution of B (= –Bz) at 1 AU. The results show that, for a given density pulse, the orientation of the corresponding transient variation of Bz has a strong relationship to the location of the density pulse and the initial conditions of the IMF. A recipe for prediction of the initial Bz turning direction is also presented in this study.In previous studies that used this recipe with only a flat HCS/HPS that was coincident with the solar equatorial plane, we found a prediction accuracy of 83% from a data set of 73 events during solar maximum. The present study that incorporates more realistic HCS/HPS tilt angles confirms the earlier work.Our study leads us to suggest that significant Bz values, associated with substantial post-shock temporal periods of hours at 1 AU, could be achieved if large energies (say, 10 32–10 33 erg) were released at the Sun in a flare or helmet de-stabilization process.  相似文献   

18.
The white light coronagraph on Skylab observed many loop type coronal transients. These loops travel through the coronagraph's field of view (2–6R ) over a period of a few hours, after which the legs of the loops usually remain visible for a few days. In this paper we investigate the temporal changes in density and mass per unit length measured along the legs of such loops during the several days after the initial eruption. Examination of 8 transients shows that the mass and density in the legs decrease during the few hours after the top of the loop has travelled beyond the coronagraph's field of view. The mass and density then increase slowly, during the next one half to one day, then decrease again over approximately the same period. These changes are generally shown to be too rapid to be explained by solar rotation, indicating that the transient legs have a lifetime of only a few days.The results of a detailed study of the transient of 10 August 1973 are compared with the results from theoretical calculations. For the top of the loop a one-dimensional flow problem is solved, assuming a balance between gravity, inertia, and pressure gradients. The legs are modeled by a flow in a tube of constant cross section. Models for the flow in the legs were calculated under the assumption that the mass distribution is close to hydrostatic equilibrium. Using these models we can estimate that approximately 5 × 1014 g of material flow outward through the legs of this transient. We also find that the best fit to the observed average density gradient is obtained with a temperature of 1.7 × 106 K.On leave from Max-Planck Institut für Physik und Astrophysik, Munich, Germany.The National Center for Atmospheric Research is sponsored by the National Science Foundation.  相似文献   

19.
Observations of a coronal transient event were obtained in white light by the Skylab coronagraph and at metric wavelengths by the radioheliograph and spectrograph at Culgoora and the spectrograph-interferometer at Boulder. The continuum radio burst was found to originate above the outward-moving white light loop - a region of compressed material headed by a bow wave. The computed density in the region of radio emission, based on either gyro-synchrotron or harmonic plasma radiation mechanisms, was approximately 10 times the ambient coronal density; this is compatible with the density deduced from the white light observations. The magnetic energy density derived from the radio observations was greater than 10 times the thermal energy density, marginally larger than the kinetic energy density in the fastest moving portion of the transient, and considerably larger in most other regions. The ambient medium, the white light front, the compression region, the loop, and the slower, massive flow of material behind are each examined. It is found that the plasma was magnetically controlled throughout, and that magnetic forces provided the principal mechanism for acceleration of the transient material from the Sun.Also, High Altitude Observatory, National Center for Atmospheric Research, Boulder, Colorado.Now at Los Alamos Scientific Laboratory, Los Alamos, New Mexico.The National Center for Atmospheric Research is sponsored by the National Science Foundation.On leave from Institute of Applied Physics, University of Berne, Switzerland.Also, Division of Radiophysics, CSIRO, Sydney, Australia.  相似文献   

20.
We observed the neutron star X-ray transient 2S 1803−245 in quiescence with the X-ray satellite XMM–Newton , but did not detect it. An analysis of the X-ray bursts observed during the 1998 outburst of 2S 1803−245 gives an upper limit to the distance of ≤7.3 kpc, leading to an upper limit on the quiescent 0.5–10 keV X-ray luminosity of  ≤2.8 × 1032 erg s−1  (3σ). Since the expected orbital period of 2S 1803−245 is several hours, this limit is not much higher than those observed for the quiescent black hole transients with similar orbital periods.  相似文献   

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