Finding bursts: the routine iris_burst_check.pro


The IDL routine iris_burst_check.pro runs through an IRIS spectral data-set and identifies which pixels qualify as bursts. For each pixel, the routine checks

  • if the average intensity over the region  ± 50 km/s from line center of Si IV 1402.77 is above a threshold value
  • if the average intensity is less than x10 the median intensity in the ± 50 km/s range

The second requirement aims to prevent intense particle hits (which usually occupy only one or two spectral pixels) from being flagged. The threshold value is determined as follows:

  • A reference threshold value of 500 DN/s is taken to apply at 22-Oct-2013 21:00 UT.
  • This reference value is scaled according to the difference in IRIS sensitivity between the data-set and the reference data-set.
  • If the data have been binned in the Y-direction, then the threshold is multiplied by Y-binning factor.

Calling sequence

The routine is available in the IRIS Solarsoft distribution and it is called as:

IDL> iris_burst_check, filename [, output=, threshold=, /no_median, ixrange=, /quiet]

OUTPUT: a structure containing information about each pixel that passes the threshold.
THRESHOLD: a value that over-rides the automatically-derived threshold.
NO_MEDIAN: if set, then the median is not checked.
IXRANGE: intended for long sit-and-stare sequences, this allows the time sequence to be shortened.
QUIET: if set, then no output is printed to the screen.

Example

The data-set of Tian et al. (2016, ApJ) from 2-May-2015 02:34 UT is used as an example.

IDL> file=iris_find_file('2-may-2015 02:34')
IDL> iris_burst_check,file,output=output

File index Event Time X-ind Y-ind Int (DN/s) npix
0 1 03:01:52 177 182 936.7 9
0 2 02:58:49 157 232 735.4 9
0 3 03:02:11 179 248 726.5 6
0 4 03:01:25 174 260 704.1 3
0 5 03:05:51 203 274 678.5 2

**NOTE: threshold adjusted for calibration and pixel-binning: 465.1 DN/s

The output text displays five events, with the time, X-index, Y-index and intensity corresponding to the brightest pixel of the event. The number of pixels belonging to each event is indicated. The threshold value for the detections is displayed.


Page maintained by Dr Peter R Young.