6 research outputs found
Observations of quasi-periodic solar X-ray emission as a result of MHD oscillations in a system of multiple flare loops
We investigate the solar flare of 20 October 2002. The flare was accompanied
by quasi-periodic pulsations (QPP) of both thermal and nonthermal hard X-ray
emissions (HXR) observed by RHESSI in the 3-50 keV energy range. Analysis of
the HXR time profiles in different energy channels made with the Lomb
periodogram indicates two statistically significant time periods of about 16
and 36 seconds. The 36-second QPP were observed only in the nonthermal HXR
emission in the impulsive phase of the flare. The 16-second QPP were more
pronounced in the thermal HXR emission and were observed both in the impulsive
and in the decay phases of the flare. Imaging analysis of the flare region, the
determined time periods of the QPP and the estimated physical parameters of
magnetic loops in the flare region allow us to interpret the observations as
follows. 1) In the impulsive phase energy was released and electrons were
accelerated by successive acts with the average time period of about 36 seconds
in different parts of two spatially separated, but interacting loop systems of
the flare region. 2) The 36-second periodicity of energy release could be
caused by the action of fast MHD oscillations in the loops connecting these
flaring sites. 3) During the first explosive acts of energy release the MHD
oscillations (most probably the sausage mode) with time period of 16 seconds
were excited in one system of the flare loops. 4) These oscillations were
maintained by the subsequent explosive acts of energy release in the impulsive
phase and were completely damped in the decay phase of the flare.Comment: 14 pages, 4 figure
Imaging Observations of Quasi-Periodic Pulsatory Non-Thermal Emission in Ribbon Solar Flares
Using RHESSI and some auxiliary observations we examine possible connections
between spatial and temporal morphology of the sources of non-thermal hard
X-ray (HXR) emission which revealed minute quasi-periodic pulsations (QPPs)
during the two-ribbon flares on 2003 May 29 and 2005 January 19. Microwave
emission also reveals the same quasi-periodicity. The sources of non-thermal
HXR emission are situated mainly inside the footpoints of the flare arcade
loops observed by the TRACE and SOHO instruments. At least one of the sources
moves systematically both during the QPP-phase and after it in each flare that
allows to examine the sources velocities and the energy release rate via the
process of magnetic reconnection. The sources move predominantly parallel to
the magnetic inversion line or the appropriate flare ribbon during the
QPP-phase whereas the movement slightly changes to more perpendicular regime
after the QPPs. Each QPP is emitted from its own position. It is also seen that
the velocity and the energy release rate don't correlate well with the flux of
the HXR emission calculated from the sources. The sources of microwaves and
thermal HXRs are situated near the apex of the loop arcade and are not
stationary either. Almost all QPPs and some spikes of HXR emission during the
post-QPP-phase reveal the soft-hard-soft spectral behavior indicating separate
acts of electrons acceleration and injection, rather than modulation of
emission flux by some kinds of magnetohydrodynamic (MHD) oscillations of
coronal loops. In all likelihood, the flare scenarios based on the successively
firing arcade loops are more preferable to interpret the observations, although
we can not conclude exactly what mechanism forces these loops to flare up.Comment: 22 pages, 10 figure
Flux-rope twist in eruptive flares and CMEs : due to zipper and main-phase reconnection
Funding: UK Science and Technology Facilities CouncilThe nature of three-dimensional reconnection when a twisted flux tube erupts during an eruptive flare or coronal mass ejection is considered. The reconnection has two phases: first of all, 3D “zipper reconnection” propagates along the initial coronal arcade, parallel to the polarity inversion line (PIL); then subsequent quasi-2D “main phase reconnection” in the low corona around a flux rope during its eruption produces coronal loops and chromospheric ribbons that propagate away from the PIL in a direction normal to it. One scenario starts with a sheared arcade: the zipper reconnection creates a twisted flux rope of roughly one turn (2π radians of twist), and then main phase reconnection builds up the bulk of the erupting flux rope with a relatively uniform twist of a few turns. A second scenario starts with a pre-existing flux rope under the arcade. Here the zipper phase can create a core with many turns that depend on the ratio of the magnetic fluxes in the newly formed flare ribbons and the new flux rope. Main phase reconnection then adds a layer of roughly uniform twist to the twisted central core. Both phases and scenarios are modeled in a simple way that assumes the initial magnetic flux is fragmented along the PIL. The model uses conservation of magnetic helicity and flux, together with equipartition of magnetic helicity, to deduce the twist of the erupting flux rope in terms the geometry of the initial configuration. Interplanetary observations show some flux ropes have a fairly uniform twist, which could be produced when the zipper phase and any pre-existing flux rope possess small or moderate twist (up to one or two turns). Other interplanetary flux ropes have highly twisted cores (up to five turns), which could be produced when there is a pre-existing flux rope and an active zipper phase that creates substantial extra twist.PostprintPublisher PDFPeer reviewe