High-cadence and high-resolution Hα imaging spectroscopy of a circular flare's remote ribbon with IBIS

Journal Article · Sat Jun 01 00:00:00 EDT 2013 · Astrophysical Journal

DOI:https://doi.org/10.1088/0004-637X/769/2/112· OSTI ID:22342073

Deng, Na; Jing, Ju; Chen, Xin; Liu, Chang; Xu, Yan; Wang, Haimin ^[1]; Tritschler, Alexandra; Reardon, Kevin ^[2]; Denker, Carsten ^[3]

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1. Space Weather Research Laboratory, New Jersey Institute of Technology, University Heights, Newark, NJ 07102-1982 (United States)
2. National Solar Observatory, Sacramento Peak, Sunspot, NM 88349-0062 (United States)
3. Leibniz-Institut für Astrophysik Potsdam, An der Sternwarte 16, D-14482 Potsdam (Germany)

We present an unprecedented high-resolution Hα imaging spectroscopic observation of a C4.1 flare taken with the Interferometric Bidimensional Spectrometer (IBIS) in conjunction with the adaptive optics system at the 76 cm Dunn Solar Telescope on 2011 October 22 in the active region NOAA 11324. Such a two-dimensional spectroscopic observation covering the entire evolution of a flare ribbon with high spatial (0.''1 pixel{sup –1} image scale), cadence (4.8 s), and spectral (0.1 Å step size) resolution is rarely reported. The flare consists of a main circular ribbon that occurred in a parasitic magnetic configuration and a remote ribbon that was observed by the IBIS. Such a circular-ribbon flare with a remote brightening is predicted in three-dimensional fan-spine reconnection but so far has been rarely studied. During the flare impulsive phase, we define 'core' and 'halo' structures in the observed ribbon based on IBIS narrowband images in the Hα line wing and line center. Examining the Hα emission spectra averaged in the flare core and halo areas, we find that only those from the flare cores show typical nonthermal electron beam heating characteristics that have been revealed by previous theoretical simulations and observations of flaring Hα line profiles. These characteristics include broad and centrally reversed emission spectra, excess emission in the red wing with regard to the blue wing (i.e., red asymmetry), and redshifted bisectors of the emission spectra. We also observe rather quick timescales for the heating (∼30 s) and cooling (∼14-33 s) in the flare core locations. Therefore, we suggest that the flare cores revealed by IBIS track the sites of electron beam precipitation with exceptional spatial and temporal resolution. The flare cores show two-stage motion (a parallel motion along the ribbon followed by an expansion motion perpendicular to the ribbon) during the two impulsive phases of the flare. Some cores jump quickly (30 km s{sup –1}) between discrete magnetic elements implying reconnection involving different flux tubes. We observe a very high temporal correlation (≳ 0.9) between the integrated Hα and hard X-rays (HXR) emission during the flare impulsive phase. A short time delay (4.6 s) is also found in the Hα emission spikes relative to HXR bursts. The ionization timescale of the cool chromosphere and the extra time taken for the electrons to travel to the remote ribbon site may contribute to this delay.

• OSTI ID: 22342073
• Journal Information: Astrophysical Journal, Vol. 769, Issue 2; Other Information: Country of input: International Atomic Energy Agency (IAEA); ISSN 0004-637X
• Country of Publication: United States
• Language: English

Related Subjects

79 ASTROPHYSICS
COSMOLOGY AND ASTRONOMY
ASYMMETRY
CHROMOSPHERE
CORRELATIONS
ELECTRON BEAMS
ELECTRONS
EMISSION
EMISSION SPECTRA
EXPANSION
GAMMA RADIATION
HARD X RADIATION
PARTICLE TRACKS
RED SHIFT
RESOLUTION
SIMULATION
SPECTROSCOPY
SUN
TELESCOPES
THREE-DIMENSIONAL CALCULATIONS
TIME DELAY
TWO-DIMENSIONAL CALCULATIONS