DG Notes on 20170904 Event

Purpose

There are various scripts for doing the imaging and self calibration, but they require explanation on how to use them. This page is meant to provide step-by-step explanation on analyzing one event, the M5.5 flare that occurred on 2017-Sep-04. I earlier did an initial study of this event, but in a hurried fashion in order to use the results for a proposal (which was successful, by the way!). I would like to do a more careful job with the initial calibration and analysis, and then continue with a second round of self calibration.

Initial Preparation

The data begin as raw data in Miriad format, recorded to disk by the pipeline system, in the form of IDB files. These files each contain 10-min of data, with several such files together representing a scan. The easiest way to identify the time period of interest is to examine the overview spectral plots on the RHESSI Browser and check "EOVSA Radio Data" on the upper left. Use the time you identified to find the corresponding IDB file(s) under /data1/eovsa/fits/IDB/yyyymmdd/ (also accessible from the EOVSA web site. The scan containing this flare is a quite long one, starting 18:53:33 UT and continuing to 21:30:00 UT or so.

To know the exact time of interest takes some iteration, especially for such a long flare with several peaks and smaller events. After some checking, I settled on the three 10-min files starting at 20:23:33, 20:33:33, and 20:43:33 UT. Undoubtedly an additional one or two 10-min intervals after the end time of 20:53:33 would be useful for following the decay of the event, but in the interests of time analysis of these will be postponed.

Applying Corrections to IDB Files

The first step is to apply two corrections to the IDB files: 1) Correct for differential feed rotation among the different types of antenna mounts, and 2) correct for attenuation changes during the burst. For this event, the following python commands do this

In [1]: import glob
In [2]: files = glob.glob('/data1/eovsa/fits/IDB/20170904/IDB*20?3*')
In [3]: files.sort()
In [4]: files
Out[4]:
 ['/data1/eovsa/fits/IDB/20170904/IDB20170904200333',
 '/data1/eovsa/fits/IDB/20170904/IDB20170904201333',
 '/data1/eovsa/fits/IDB/20170904/IDB20170904202333',
 '/data1/eovsa/fits/IDB/20170904/IDB20170904203333',
 '/data1/eovsa/fits/IDB/20170904/IDB20170904204333',
 '/data1/eovsa/fits/IDB/20170904/IDB20170904205333']
In [5]: import pipeline_cal as pc
In [6]: for file in files[2:5]:
   ...:     pc.udb_corr([file])
   ...:

This will result in the three files, IDB20170904202333, IDB20170904203333, and IDB20170904204333 being corrected and written to the current directory. Each file takes roughly 2 minutes to process.