What is the true nature of blinkers?

S. Subramanian, M. S. Madjarska, J. G. Doyle and D. Bewsher

Fig 10: he coronal bright point jet B1 Fig. 8) showing expansion and eruption of loop structures as observed in XRT Al poly and EUVI 171 Å images. The bottom panel shows the light-curves of the blinker event B1 peaking simultaneously in XRT (grey line) and EUVI 171 Å (black line).

Aims. The aim of this work is to identify the true nature of the transient EUV brightenings, called blinkers.

Methods Co-spatial and co-temporal multi-instrument data, including imaging (EUVI/STEREO, XRT and SOT/Hinode), spectro- scopic (CDS/SoHO and EIS/Hinode) and magnetogram (SOT/Hinode) data, of an isolated equatorial coronal hole were used. An automatic program for identifying transient brightenings in CDS O V 629 Å and EUVI 171 Å was applied.

Results. We identified 28 blinker groups in the CDS O V 629 Å raster images. All CDS O V 629 Å blinkers showed counterparts in EUVI 171 Å and 304 Å images. We classified these blinkers into two categories, one associated with coronal counterparts and other with no coronal counterparts as seen in XRT images and EIS Fe XII 195.12 Å raster images. Around two-thirds of the blinkers show coronal counterparts and correspond to various events like EUV/X-ray jets, brightenings in coronal bright points or foot-point bright- enings of larger loops. These brightenings occur repetitively and have a lifetime of around 40 min at transition region temperatures. The remaining blinker groups with no coronal counterpart in XRT and EIS Fe XII 195.12 Å appear as point-like brightenings and have chromospheric/transition region origin. They take place only once and have a lifetime of around 20 minutes. In general, lifetimes of blinkers are different at different wavelengths, i.e. different temperatures, decreasing from the chromosphere to the corona. Conclusions. This work shows that the term blinker covers a range of phenomena. Blinkers are the EUV response of various transient events originating at coronal, transition region and chromospheric heights. Hence, events associated with blinkers contribute to the formation and maintenance of the temperature gradient in the transition region and the corona.

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Last Revised: 2011 November 7th