IRIS burst properties in active regions

Abstract

Context. Interface Region Imaging Spectrograph (IRIS) bursts are localised features thought to be driven by magnetic reconnection. Although these events are well-studied, it remains unknown whether their properties vary as their host active regions (ARs) evolve. Aims. In this article, we aim to understand whether the measurable properties (e.g. frequency, area, location, spectral characteristics) of IRIS bursts are consistent during the evolution of their host ARs. Methods. We study 42 dense 400-step rasters sampled by IRIS. These rasters each covered one of seven ARs, with each AR being sampled at least four times over a minimum of 48 h. An automated IRIS burst detection algorithm is used to identify IRIS burst profiles in this work. Data from the Solar Dynamics Observatory’s Helioseismic and Magnetic Imager are also used to provide context about the co-spatial line-of-sight magnetic field. Results. Of the rasters studied, 36 (86%) were found to contain IRIS burst profiles. Five ARs (11850, 11909, 11916, 12104, and 12139) contained IRIS burst profiles in each raster that sampled them whilst one AR (11871) was found to contain no IRIS burst profiles at any time. A total of 4019 IRIS burst profiles belonging to 752 connected objects, which we define as parent IRIS bursts, were studied. IRIS burst profiles were only detected within compact regions in each raster, with these regions appearing to increase in size as the host ARs aged. No systematic changes in the frequency of IRIS burst profiles or the spectral characteristic of IRIS burst profiles through time were found for these ARs. Finally, 93% of parent IRIS bursts with areas between 1 arcsec2 and 4 arcsec2 were observed to occur co-spatial to bi-poles in the photosphere. Conclusions. IRIS bursts are small-scale brightenings which have remarkably consistent spectral and spatial properties throughout the evolution of ARs. These events predominantly form within the cores of larger and more complex ARs, with the regions containing these events appearing to increase in size as the host region itself evolves.