Matched Filter imaging - askap-craco/CELEBI GitHub Wiki

The conventional method used in CELEBI to image the FRB is inefficient due to the large window in time that is taken due to imprecise timestamping of the FRB position when detected by ASKAP. By default this window is ~11 ms wide, but this can vary. Most FRBs are 1- a few ms wide and even posses often complicated time and frequency structure.

Matched Filter imaging aims to solve these issues. The basic workflow includes:

  1. Using the HTR data to produce

    • HTR binconfig file encompassing the FRB and RFI surrounding the FRB
    • Time and frequency weights that replicate the structure of the FRB that

  2. Correlate the data using the new binconfig file to produce .difx data

  3. Apply time and freq weights to .difx data, subtract RFI visibilities from FRB visibilities and scrunch in time to produce a single bin

  4. Image FRB

Parameters for making binconfig file

params.mf_thres = 0.15 - % of peak value of FRB to use as a threshold for choosing on-pulse FRB bins
params.mf_tN = 108 - Initial bin resolution in micro-seconds
params.mf_rms_w = 0.025 - phase width of off-pulse region to estimate rms
params.mf_rms_g = 0.1 - region of data in phase units used to separate the rms off-pulse region and FRB on-pulse region \
params.mf_rfi_w = 3.0 - width of rfi off-pulse region in ms to take as bins for rfi subtraction \ params.mf_rfi_g = 1.0 - region in ms between rfi off-pulse region and FRB on-pulse region
params.mf_fw = True - Calculate frequency-dependent weights to apply to visibility data, if False, will set all frequency channel weights to 1
params.mf_tw = True - Calculate time-dependent weights to apply to visibility data, if False, will set all time bin weights to 1

NOTE: When making the binconfig file, the number of bins to correlate cannot exceed MAXBINS = 140 without substantially increasing the memory usage. Thus an algorithm is put in place to dynamically set the bin resolution given the FRB width and rfi width.

NOTE: The bin resolution should always be a multiple of 108 for optimal compatibility with DIFX.

Parameters for imaging Matched filter FRB

params.mfimagesize = 1000 size of image in pixels
params.mfpixelsize = 1 pixel resolution in arcseconds