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/___/____\____/|__/|__/    SPOTLIGHT Lag Of Wavefronts

SPOTLIGHT Lag Of Wavefronts

Estimating the burst arrival time offset between SPOTLIGHT’s Beam data and Visibility data

Repository for details of burst ToA offset estimation experiment.
Check the Final Report here
~ Raghav Wani, August 2025

Essential Scripts:

• make_pc_beam.py
  Python script developed by Arpan to make PC beam from visibility raw data. It stores PC beam data in dat file.
  Usage:

   python3 make_pc_beam.py -f Visi-R*.raw \
   	--freq-start 550e6 --freq-end 750e6 \
   	--channels 4096 --output 30ant.dat \
   	--antmask 0x738ffff --no-bandpass --no-baseline
  

• dat_to_beam.py
  Python script to convert dat file generated by make_pc_beam.py into a filterbank file.
  Usage:
  python dat_to_beam.py then enter input details

• presto_timeseries.py
  Python script to plot de-dispersed timeseries from dat file and estimate burst toa offset, for comparing visibility and beam data.
  Usage:
  python presto_timeseries.py then enter input details

• gwb_vs_splt_presto_timeseries.py Python script to plot de-dispersed timeseries from dat file and estimate burst toa offset, mainly for comparing burst profiles from GWB with SPOTLIGHT beam data.
  Usage:
  python gwb_vs_splt_presto_timeseries.py then enter input details

File structure of .dat file made from raw visibility data

Header (44 bytes):

• 5 doubles → (freq_start, freq_end, channel_width, integration_time, processing_timestamp)
• 1 integer → channels

Data Records:

• 8-byte timestamp (double, Unix time with μs precision)
• 4096 × 4-byte floats → beam power data
• Each record = 1.31072 ms integrated beam data (550–750 MHz, 4096 channels).

Supporting Tools

• Raw data from filterbank file

   dd if=BM24.fil of=BM24.hdr bs=1 count=345 # Makes header file 
   dd if=BM24.fil of=BM24.raw bs=1M skip=345 iflag=skip_bytes # Makes raw file
  

• Re-scaling the raw data:

   ./read_PAbeam.8bit.PC_beam.noscale.offset <input data file name> \
     <output file name> <observation duration in seconds> \
     <Frequency channel> <input time resolution in sec> \
     <integration factor for PA beam> <scaling factor>
   

Example: ./read_PAbeam.8bit.PC_beam.noscale.offset BM7.raw BM7_offset64.raw 550 4096 0.00131072 1 64

• Making filterbank after re-scaling

   cat BM7.hdr BM7_offset64.raw > BM7_offset64.fil