Investigating datasets with high IRIS burst prevalence

Abstract

Context. Approximately 0.01% of all Si IV 1394 Å spectra sampled in 2013 and 2014 by the Interface Region Imaging Spectrograph (IRIS) have IRIS burst profiles. However, these events are not evenly distributed across datasets with 19.31% of these spectra being identified in only six (of more than 3500) rasters. Aims. Here, we investigate five of these six datasets, with the aim of understanding why they contain so many IRIS burst profiles. This research will help guide future targeted analyses of IRIS bursts. Methods. We analyse five datasets sampled by the IRIS satellite, studying both Si IV 1394 Å spectra and 1400 Å filter slit-jaw imager (SJI) data. IRIS burst profiles are identified through the use of an automated algorithm. Additionally, we study co-spatial line-of-sight photospheric magnetic field maps sampled by the Solar Dynamics Observatory’s Helioseismic and Magnetic Imager (SDO/HMI) instrument. Results. The majority of identified IRIS burst profiles (12 401 out of 13 904) found in the five datasets analysed here were localised to seven small regions in the time-distance domain (temporal durations of < 4 h and spatial lengths of < 12″ along the slit). The SJI data co-spatial to these regions contained long-lived or repetitive compact brightenings, matching the defined properties of UV bursts, which remained close to the IRIS slit throughout their evolutions. The IRIS burst profiles were not limited to the brightest pixels in the fields of view (FOVs) nor did they comprise the majority of bright (> 500 DN/s) pixels. These IRIS burst profiles occurred co-spatial to evolving (e.g., cancelling) opposite polarity magnetic fields where magnetic reconnection is thought to be possible. Conclusions. More than 10% of the IRIS burst profiles identified during the entirety of 2013 and 2014 are contained in just seven small regions in the time-distance domain where long-lived (lifetimes > 10 min) or repetitive UV bursts occurred along the axis of the IRIS slit.