EVLA Wide-Band Wide-Field Imaging: G55.7 3.4

Overview

This CASA Guide describes the imaging of the supernova remnant G55.7+3.4.. The data were taken on August 23, 2010, in the first D-configuration for which the new wide-band capabilities of the WIDAR correlator were available. The 8-hour-long observation includes all available 1 GHz of bandwidth in L-band, from 1-2 GHz in frequency.

The measurement set (MS) which provides a starting point for this Guide has been imported from the SDM file set and time-averaged to 10 seconds. Both of these options are available from the NRAO data archive, and since this operation can be relatively time-consuming, the imported, time-averaged dataset is being provided. The original data set can be found [here]; note that it is 170 GB in raw form.

Averaging to 10 seconds and the removal of some scans which are not used in this tutorial reduces the size of the data set to around 14 GB; the addition of columns for model and corrected data (known as "scratch columns") returns it to 43 GB, which is the size of the MS which will be used here.

[Instructions on locating data at the workshop... and from outside the workshop.]

Preliminary data evaluation

Start CASA by typing casapy-stable on the command line. If you have not used CASA before, some helpful tips are available on the Getting Started in CASA page.

As a first step, use listobs to have a look at the MS:

# In CASA
listobs('G55.7+3.4_10s.ms')

The logger output will look like this:

A priori calibration and flagging

Before we proceed with further processing, we should check the observation log to see if there were any issues noted during the run that need to be addressed. The log can be found at

Automatic RFI excision

Evaluating results & manual flagging

Flagging lowest edge of SPW 0 ...