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We present the analysis of an XMM-Newton observation of the Seyfert galaxy NGC 2992. The source was found in its highest level of X-ray activity yet detected, a factor ~23.5 higher in the 2-10?keV flux than the historical minimum. NGC 2992 is known to exhibit X-ray flaring activity on timescales of days to weeks, and the XMM-Newton data provide at least a factor of ~3 better spectral resolution in the Fe K band than any previously measured flaring X-ray state. We find that there is a broad feature in the ~5-7?keV band that could be interpreted as a relativistic Fe K? emission line. Its flux appears to have increased in tandem with the 2-10?keV continuum when compared to a previous Suzaku observation when the continuum was a factor of ~8 lower than that during the XMM-Newton observation. The XMM-Newton data are consistent with the general picture that increased X-ray activity and corresponding changes in the Fe K? line emission occur in the innermost regions of the putative accretion disk. This behavior contrasts with the behavior of other active galactic nuclei in which the Fe K? line does not respond to variability in the X-ray.

We extend the study of the core of the Fe K$\alpha$ emission line at \sim 6.4 keV in Seyfert galaxies reported in Yaqoob & Padmanabhan (2004) using a larger sample observed by the Chandra High Energy Grating (HEG). Whilst heavily obscured active galactic nuclei (AGNs) are excluded from the sample, these data offer some of the highest precision measurements of the peak energy of the Fe K$\alpha$ line, and the highest spectral resolution measurements of the width of the core of the line in unobscured and moderately obscured ($N_{H}, Comment: 54 pages, 7 figures, and 4 tables, to appear in ApJ Supplement Series

We propose a flux-rope model for the initiation of flare-associated CMEs. The model triggers the eruption with a catastrophic loss of MHD equilibrium and then requires magnetic reconnection to sustain the eruption's acceleration. We carry out 2.5-dimensional time-dependent resistive MHD simulations, choosing the initial state such that a flux rope embedded in a quadrupole field is attached to the solar surface; we then increase the magnetic flux of the rope by two different amounts, thus obtaining two cases. One exhibits a gradual acceleration of the flux rope, whereas the other produces an immediate acceleration. In both cases, the maximum speed of the flux rope is representative of a fast CME. Thus, we conclude that the flux-rope dynamics depends on the intensity of the emergent magnetic flux. Our model does reproduce the three-component structure of CMEs.

We describe a clear case of the initiation of a propagating bright arc and a CME on 2002 December 28, which were associated with an eruptive prominence. In EIT 304 and 195 8 images, a very long filament showed evidence of severe twisting in one of its fragments, which appeared as a prominence on December 26; then, the prominence showed the conversion of its twist into writhe. Two days later, the prominence displayed a slow rising motion for hours. Internal twisting and mass motion took place before the rapid acceleration and final eruption. The propagating bright arc and the following CME corresponded to the early rising and the subsequently eruptive phases of the prominence, respectively. Signatures of magnetic reconnection, i.e., a cusp structure and postflare loops in EUV wave bands and hard X-ray sources in the corona, were observed after the prominence eruption. It appears that the kink instability and the mass drainage in the prominence played key roles in triggering the initiation of the CME. However, the rather impulsive acceleration of the CME resulted from magnetic reconnection beneath the filament.

Using a relaxation method based on time-dependent ideal magnetohydrodynamic simulations, we find 2.5-dimensional force-free field solutions in spherical geometry, which are associated with an isolated flux rope embedded in a quadrupolar background magnetic field. The background field is of Antiochos type, consisting of a dipolar and an octopolar component with a neutral point somewhere in the equatorial plane. The flux rope is characterized by its magnetic fluxes, including the annular flux Φp and the axial magnetic flux Φ, and its geometric features described by the height of the rope axis and the length of the vertical current sheet below the rope. It is found that for a given Φp, the force-free field exhibits a complex catastrophic behavior with respect to increasing Φ. There exist two catastrophic points, and the catastrophic amplitude, measured by the jump in the height of the rope axis, is finite for both catastrophes. As a result, the flux rope may levitate stably in the corona after catastrophe, with a transverse current sheet above and a vertical current sheet below. The magnetic energy threshold for the two successive catastrophes are found to be larger than the corresponding partly open field energy. We argue that it is the transverse current sheet formed above the flux rope that provides a downward Lorentz force on the flux rope and thus keeps the rope levitating stably in the corona.

A possible explanation is proposed for the double-power-law energy spectrum of electrons from solar 3He-rich events. According to the two-stage acceleration model that was developed by Zhang for the heating and acceleration of ions and electrons in solar 3He-rich events, the energy spectrum of electrons in the thermal to power law energy range is derived. It is shown that the electron flux generally includes a thermal component at low energies and a nonthermal component with a power-law spectrum at high energies. To have the double-power-law energy spectrum of electrons at the high energies, three empirical models are proposed in terms of the dependences of the spectral power index, the electron temperature, and the threshold energy on the electron energy. The numerical result obtained by this study for the energy spectrum of electrons at energies ~1-200 keV fits very well with the double-power-law spectrum measurement given by Reames, von Rosenvinge, & Lin.

Preferential heating and abundance enhancements of carbon (C), nitrogen (N), and oxygen (O) in solar 3He-rich energetic particles are investigated in terms of the two-stage acceleration model proposed by Zhang. It is shown that C+5, N+6, and O+7 are preferentially heated by H-cyclotron waves with a frequency close to twice the 3He-cyclotron frequency through the third harmonic resonance. If the initial electron temperature of the solar corona is in the range of ~2-3.2 MK, the abundance of N in high-energy particles due to the second-stage acceleration is enhanced by a factor of ~4-12 relative to C and O. The abundance pattern of C, N, and O obtained from the two-stage acceleration model is consistent with recent measurements (Mason, Mazur, & Dwyer). In addition, harmonic resonances of neon, silicon, magnesium, sulfur, calcium, and iron with the H-cyclotron waves are discussed.

We present the first set of examples of the shrinkage of large-scale nonflare loops in the solar corona, observed by the Yohkoh Soft X-Ray Telescope in 1993 February. A large and isolated active region exhibited an unusual south-north asymmetry in coronal dynamics and heating. The northern part, referred to the main magnetic axis, showed episodic expansion and heating. In contrast, the southern part displayed obvious shrinking and cooling. This asymmetry was correlated with a severe asymmetry in the surface magnetic activity revealed by Huairou vector magnetograms. Observations suggest that this shrinkage is not an apparent motion, but a real contraction of coronal loops that brighten as a result of heating at footpoints followed by gradual cooling.

Based on combined observations from the Interface Region Imaging Spectrograph (IRIS) spectrometer with the coronal emission line of Fe xxi at 1354.08 A and SDO/AIA images in multiple passbands, we report the finding of the precursor activity manifested as the transverse oscillation of a sigmoid, which is likely a pre-existing magnetic flux rope (MFR), that led to the onset of an X class flare and a fast halo coronal mass ejection (CME) on 2014 September 10. The IRIS slit is situated at a fixed position that is almost vertical to the main axis of the sigmoid structure that has a length of about 1.8 × 105 km. This precursor oscillation lasts for about 13 minutes in the MFR and has velocities in the range of [−9, 11] km s−1 and a period of ~280 s. Our analysis, which is based on the temperature, density, length, and magnetic field strength of the observed sigmoid, indicates that the nature of the oscillation is a standing wave of fast magnetoacoustic kink mode. We further find that the precursor oscillation is excited by the energy released through an external magnetic reconnection between the unstable MFR and the ambient magnetic field. It is proposed that this precursor activity leads to the dynamic formation of a current sheet underneath the MFR that subsequently reconnects to trigger the onset of the main phase of the flare and the CME.

With the unique data set from full-disk observations provided by Michelson Doppler Imager on board the Solar and Heliospheric Observatory in the interval embodying solar cycle 23, we have found that the cyclic variations of numbers and total flux of these small-scale magnetic elements covering fluxes of (2.9-32.0) Multiplication-Sign 10{sup 18} Mx and (4.27-38.01) Multiplication-Sign 10{sup 19} Mx show anticorrelation and correlation with sunspots, respectively. In this study, the time-latitude distributions of these anticorrelated and correlated elements are analyzed. The following results are disclosed: (1) for the correlated elements, the cyclic variations of the total flux in low-latitude and middle-latitude regions show a longer duration of cyclic maximum phase than that of an active region (AR) in the corresponding latitude region; the total flux of these elements shows the accordant south-north asymmetry with that of AR; the time-latitude distribution of their number displays a similar butterfly diagram but with a latitude distribution that is twice as wide as that of sunspots. (2) For the anticorrelated elements, the time-latitude distribution of number shows a solar cycle variation different from the sunspot butterfly diagram; in each latitude, the distribution of anticorrelated elements always shows the anticorrelated variation with that of sunspots; duringmore » solar cycle 23, the average speed of the peak latitudinal migration for anticorrelated elements reaches 7.5 deg year{sup -1}, almost three times that for sunspots. These results seem to imply that the correlated elements are the debris of decayed sunspots, and the anticorrelated elements have a different source but are affected or modulated by sunspot magnetic field.« less

With the unique database from Michelson Doppler Imager aboard the Solar and Heliospheric Observatory in an interval embodying solar cycle 23, the cyclic behavior of solar small-scale magnetic elements is studied. More than 13 million small-scale magnetic elements are selected, and the following results are unclosed. (1) The quiet regions dominated the Sun's magnetic flux for about 8 years in the 12.25 year duration of Cycle 23. They contributed (0.94 - 1.44) $\times 10^{23}$ Mx flux to the Sun from the solar minimum to maximum. The monthly average magnetic flux of the quiet regions is 1.12 times that of active regions in the cycle. (2) The ratio of quiet region flux to that of the total Sun equally characterizes the course of a solar cycle. The 6-month running-average flux ratio of quiet region had been larger than 90.0% for 28 continuous months from July 2007 to October 2009, which characterizes very well the grand solar minima of Cycles 23-24. (3) From the small to large end of the flux spectrum, the variations of numbers and total flux of the network elements show no-correlation, anti-correlation, and correlation with sunspots, respectively. The anti-correlated elements, covering the flux of (2.9 - 32.0)$\times 10^{18}$ Mx, occupies 77.2% of total element number and 37.4% of quiet Sun flux. These results provide insight into reason for anti-correlated variations of small-scale magnetic activity during the solar cycle., Comment: 21 pages, 6 figures, Accepted by ApJ