Search for Microflaring Activity in the Magnetic Network

摘要

We analyze the temporal behavior of network bright points (NBPs) searching for low-atmosphere signatures of flares occurring on the magnetic network. We make use of a set of data acquired during coordinated observations between ground-based observatories (NSO/Sacramento Peak) and the MDI instrument on board SOHO. Light curves in chromospheric spectral lines show only small-amplitude temporal variations, without any sudden intensity enhancement that could suggest the presence of a transient phenomenon such as a (micro)flare. Only one NBP shows spikes of downward velocity, of the order of 2–4 km s−1, considered as signals of compression associated with a (micro)flare occurrence. For this same NBP, we also find a peculiar relationship between the magnetic and velocity fields fluctuations, as measured by MDI. Only for this point the B−V fluctuations are well correlated, suggesting the presence of magneto-acoustic waves propagating along the magnetic structure. This correlation is lost during the compression episodes and resumes afterward. An A6 GOES soft X-ray burst is temporally associated with the downward velocity episodes, suggesting that this NBP is the footpoint of a flaring loop. This event has a total thermal energy content of about 1028 erg, and, hence, belongs to the microflare class.