Statistical Analysis of Small Ellerman Bomb Events
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The properties of Ellerman bombs (EBs), small-scale brightenings in the Hα line wings, have proved difficult to establish because their size is close to the spatial resolution of even the most advanced telescopes. Here, we aim to infer the size and lifetime of EBs using high-resolution data of an emerging active region collected using the Interferometric BIdimensional Spectrometer (IBIS) and Rapid Oscillations of the Solar Atmosphere (ROSA) instruments as well as the Helioseismic and Magnetic Imager (HMI) onboard the Solar Dynamics Observatory (SDO). We develop an algorithm to track EBs through their evolution, finding that EBs can often be much smaller (around 0.3″) and shorter-lived (less than one minute) than previous estimates. A correlation between G-band magnetic bright points and EBs is also found. Combining SDO/HMI and G-band data gives a good proxy of the polarity for the vertical magnetic field. It is found that EBs often occur both over regions of opposite polarity flux and strong unipolar fields, possibly hinting at magnetic reconnection as a driver of these events.The energetics of EB events is found to follow a power-law distribution in the range of a nanoflare (1022−25 ergs).
KeywordsActive regions Magnetic fields Photosphere-sunspots Penumbra
Research at the Armagh Observatory is grant-aided by the N. Ireland Dept. of Culture, Arts and Leisure. We thank the National Solar Observatory/Sacramento Peak for their hospitality and in particular Doug Gilliam for his excellent help during the observations. We thank the UK Science and Technology Facilities Council for the studentships (CJN and SJM), PATT and support, plus support from grant ST/J001082/1. RE is thankful to the NSF, Hungary (OTKA, Ref. No. K83133) and acknowledges M. Kéray for patient encouragement. We thank Friedrich Wöger for his Image Reconstruction code and S.B. Nicholson for the connected-objects algorithm adapted for this study. The research leading to these results has received funding from the European Commission’s Seventh Framework Programme (FP7/2007-2013) under the grant agreement eHeroes (project no. 284461, http://www.eheroes.eu ). MM would like to thank the Air Force Office of Scientific Research, Air Force Material Command, USAF for sponsorship under grant number FA8655-09-13085. HMI data courtesy SDO (NASA) and the HMI consortium.