Fan-spine topology formation through two-step reconnection driven by twisted flux emergence

We address the formation of 3D nullpoint topologies in the solar corona by combining Hinode/XRT observations of a small dynamic limb event, which occurred beside a non-erupting prominence cavity, with a 3D zero-beta MHD simulation. To this end, we model the boundary-driven kinematic emergence of a compact, intense, and uniformly twisted flux tube into a potential field arcade that overlies a weakly twisted coronal flux rope. The expansion of the emerging flux in the corona gives rise to the formation of a nullpoint at the interface of the emerging and the pre-existing fields. We unveil a two-step reconnection process at the nullpoint that eventually yields the formation of a broad 3D fan-spine configuration above the emerging bipole. The first reconnection involves emerging fields and a set of large-scale arcade field lines. It results in the launch of a torsional MHD wave that propagates along the arcades, and in the formation of a sheared loop system on one side of the emerging flux. The second reconnection occurs between these newly formed loops and remote arcade fields, and yields the formation of a second loop system on the opposite side of the emerging flux. The two loop systems collectively display an anenome pattern that is located below the fan surface. The flux that surrounds the inner spine field line of the nullpoint retains a fraction of the emerged twist, while the remaining twist is evacuated along the reconnected arcades. The nature and timing of the features which occur in the simulation do qualititatively reproduce those observed by XRT in the particular event studied in this paper. Moreover, the two-step reconnection process suggests a new consistent and generic model for the formation of anemone regions in the solar corona.Comment: Accepted for publication in ApJ, 11 pages and 5 figure

Resolving the large scale spectral variability of the luminous Seyfert 1 galaxy 1H 0419-577: Evidence for a new emission component and absorption by cold dense matter

An XMM-Newton observation of the luminous Seyfert 1 galaxy 1H 0419-577 in September 2002, when the source was in an extreme low-flux state, found a very hard X-ray spectrum at 1-10 keV with a strong soft excess below ~1 keV. Comparison with an earlier XMM-Newton observation when 1H 0419-577 was `X-ray bright' indicated the dominant spectral variability was due to a steep power law or cool Comptonised thermal emission. Four further XMM-Newton observations, with 1H 0419-577 in intermediate flux states, now support that conclusion, while we also find the variable emission component in intermediate state difference spectra to be strongly modified by absorption in low ionisation matter. The variable `soft excess' then appears to be an artefact of absorption of the underlying continuum while the `core' soft emission can be attributed to recombination in an extended region of more highly ionised gas. We note the wider implications of finding substantial cold dense matter overlying (or embedded in) the X-ray continuum source in a luminous Seyfert 1 galaxy.Comment: 34 pages, 15 figures, submitted to Ap

The XMM-Newton Iron Line Profile of NGC 3783

We report on observations of the iron K line in the nearby Seyfert 1 galaxy, NGC 3783, obtained in a long, 2 orbit (240 ks) XMM-Newton observation. The line profile obtained exhibits two strong narrow peaks at 6.4 keV and at 7.0 keV, with measured line equivalent widths of 120 and 35 eV respectively. The 6.4 keV emission is the K-alpha line from near neutral Fe, whilst the 7.0 keV feature probably originates from a blend of the neutral Fe K-beta line and the H-like line of Fe at 6.97 keV. The relatively narrow velocity width of the K-alpha line (<5000 km/s), its lack of response to the continuum emission on short timescales and the detection of a neutral Compton reflection component are all consistent with a distant origin in Compton-thick matter such as the putative molecular torus. A strong absorption line from highly ionized iron (at 6.67 keV) is detected in the time-averaged iron line profile, whilst the depth of the feature appears to vary with time, being strongest when the continuum flux is higher. The iron absorption line probably arises from the highest ionization component of the known warm absorber in NGC 3783, with an ionization of logxi=3 and column density of 5x10^{22}cm{-2} and may originate from within 0.1pc of the nucleus. A weak red-wing to the iron K line profile is also detected below 6.4 keV. However when the effect of the highly ionized warm absorber on the underlying continuum is taken into account, the requirement for a relativistic iron line component from the inner disk is reduced.Comment: 34 pages, including 11 figures. Accepted for publication in Ap

An XMM-Newton observation of the Narrow Line Seyfert 1 Galaxy, Markarian 896

XMM-Newton observations of the NLS1 Markarian 896 are presented. Over the 2-10 keV band, an iron emission line, close to 6.4 keV, is seen. The line is just resolved and has an equivalent width of ~170 eV. The broad-band spectrum is well modelled by a power law slope of gamma ~ 2.03, together with two blackbody components to fit the soft X-ray excess. Using a more physical two-temperature Comptonisation model, a good fit is obtained for an input photon distribution of kT ~ 60eV and Comptonising electron temperatures of ~0.3 and 200 keV. The soft excess cannot be explained purely through the reprocessing of a hard X-ray continuum by an ionised disc reflector.Comment: 6 pages, 4 figures, accepted by MNRA

Fe K emission and absorption features in XMM-Newton spectra of Mkn 766 - evidence for reprocessing in flare ejecta

We report on the analysis of a long XMM-Newton EPIC observation in 2001 May of the Narrow Line Seyfert 1 galaxy Mkn 766. The 3-11 keV spectrum exhibits a moderately steep power law continuum, with a broad emission line at ~6.7 keV, probably blended with a narrow line at ~6.4 keV, and a broad absorption trough above ~8.7 keV. We identify both broad spectral features with reprocessing in He-like Fe. An earlier XMM-Newton observation of Mkn 766 in 2000 May, when the source was a factor ~2 fainter, shows a similar broad emission line, but with a slightly flatter power law and absorption at a lower energy. In neither observation do we find a requirement for the previously reported broad 'red wing' to the line and hence of reflection from the innermost accretion disc. More detailed examination of the longer XMM-Newton observation reveals evidence for rapid spectral variability in the Fe K band, apparently linked with the occurrence of X-ray 'flares'. A reduction in the emission line strength and increased high energy absorption during the X-ray flaring suggests that these transient effects are due to highly ionised ejecta associated with the flares. Simple scaling from the flare avalanche model proposed for the luminous QSO PDS 456 (Reeves etal. 2002) confirms the feasibility of coherent flaring being the cause of the strong peaks seen in the X-ray light curve of \mkn.Comment: 9 pages, 11 figures, submitted to MNRA

Relativistic Iron K Emission and absorption in the Seyfert 1.9 galaxy MCG-5-23-16

We present the results of the simultaneous deep XMM and Chandra observations of the bright Seyfert 1.9 galaxy MCG-5-23-16, which is thought to have one of the best known examples of a relativistically broadened iron K-alpha line. The time averaged spectral analysis shows that the iron K-shell complex is best modeled with an unresolved narrow emission component (FWHM < 5000 km/s, EW ~ 60 eV) plus a broad component. This latter component has FWHM ~ 44000 km/s and EW ~ 50 eV. Its profile is well described by an emission line originating from an accretion disk viewed with an inclination angle ~ 40^\circ and with the emission arising from within a few tens of gravitational radii of the central black hole. The time-resolved spectral analysis of the XMM EPIC-pn spectrum shows that both the narrow and broad components of the Fe K emission line appear to be constant in time within the errors. We detected a narrow sporadic absorption line at 7.7 keV which appears to be variable on a time-scale of 20 ksec. If associated with Fe XXVI Ly-alpha this absorption is indicative of a possibly variable, high ionization, high velocity outflow. The variability of this absorption feature appears to rule out a local (z=0) origin. The analysis of the XMM RGS spectrum reveals that the soft X-ray emission of MCG-5-23-16 is likely dominated by several emission lines superimposed on an unabsorbed scattered power-law continuum. The lack of strong Fe L shell emission together with the detection of a strong forbidden line in the O VII triplet is consistent with a scenario where the soft X-ray emission lines are produced in a plasma photoionized by the nuclear emission.Comment: 45 pages, 12 figures, 4 tables, accepted for publication in Ap

Morphology Of A Hot Prominence Cavity Observed with Hinode/XRT and SDO/AIA

Prominence cavities appear as circularly shaped voids in coronal emission over polarity inversion lines where a prominence channel is straddling the solar limb. The presence of chromospheric material suspended at coronal altitudes is a common but not necessary feature within these cavities. These voids are observed to change shape as a prominence feature rotates around the limb. We use a morphological model projected in cross-sections to fit the cavity emission in Hinode/XRT passbands, and then apply temperature diagnostics to XRT and SDO/AIA data to investigate the thermal structure. We find significant evidence that the prominence cavity is hotter than the corona immediately outside the cavity boundary. This investigation follows upon "Thermal Properties of A Solar Coronal Cavity Observed with the X-ray Telescope on Hinode" by Reeves et al., 2012, ApJ, in press

Posteruptive phenomena in coronal mass ejections and substorms: Indicators of a universal process?

[1] We examine phenomena associated with eruptions in the two different regimes of the solar corona and the terrestrial magnetosphere. We find striking similarities between the speeds of shrinking magnetic field lines in the corona and dipolarization fronts traversing the magnetosphere. We also examine the similarities between supra-arcade downflows observed during solar flares and bursty bulk flows seen in the magnetotail and find that these phenomena have remarkably similar speeds, velocity profiles, and size scales. Thus we show manifest similarities in the magnetic reconfiguration in response to the ejection of coronal mass ejections in the corona and the ejection of plasmoids in the magnetotail. The subsequent return of loops to a quasi-potential state in the corona and field dipolarization in the magnetotail are physical analogs and trigger similar phenomena such as downflows, which provides key insights into the underlying drivers of the plasma dynamics