Astronomy and Astrophysics – Astronomy
Scientific paper
May 2010
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2010aas...21640418b&link_type=abstract
American Astronomical Society, AAS Meeting #216, #404.18; Bulletin of the American Astronomical Society, Vol. 41, p.902
Astronomy and Astrophysics
Astronomy
Scientific paper
A GOES B1.8 microflare was observed with RHESSI and SOHO's CDS between about 16:25 and 17:00 UT on 2009 July 5. The event occurred in NOAA AR 11024, the only active region on the solar disk at the time. With CDS we obtained rapid cadence (7 s) stare spectra within a narrow field of view toward the center of the region. Spectra contain emission lines from ions that cover a wide range of temperature, including He I (0.01 MK), O V (0.25 MK), Si XII (2 MK), and Fe XIX (8 MK). The start of a burst in He I and O V line emission preceded the emergence of Fe XIX line emission by about 1 minute, and the emergence of 3-12 keV X-ray emission by about 4 minutes. Thus the onset of the flare is observed in upper chromospheric (He I) and transition region (O V) line emission before it is detected in high temperature flare plasma emission. This may indicate the presence of a nonthermal particle beam early during the microflare. Similarly, in subsequent bursts the O V and He I intensities increase before emissions from the hot flare plasma. In intervals lasting up to about 3 minutes during several bursts, the He I and O V emission line profiles show secondary, highly blueshifted ( 200 km/s) components; during intervals lasting nearly 1 minute the velocities of the primary and secondary components are oppositely directed, suggesting explosive chromospheric evaporation. This work is supported by NASA through SR&T grant NNX07AI09G.
Brosius Jeffrey W.
Holman Gordon D.
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