WORKSHOP 2020

2-6 November 2020

Millimeter VLBI with rpicard

MICHAEL JANSSEN

Radboud PIpeline for the Calibration of high Angular Resolution Data (rPICARD)

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• Janssen et al., A&A, 626 (2019) A75.
• The Event Horizon Telescope Collaboration,�2019, ApJL, 875, L3.
• https://bitbucket.org/M_Janssen/picard�
• Based on CASA6 with own plotting functions.�
• Many diagnostics, easy to tune parameters + re-run.�
• For many arrays: EHT, GMVA, VLBA, EVN, …

Pipeline setup (1/3)

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• Singularity, Docker, or from source:
• http://www.jive.nl/jivewiki/doku.php?id=casa:casa�
• Using Singularity ( https://singularity.lbl.gov/ ) in the working dir:

$ singularity build casavlbi.pipe docker://mjanssen2308/casavlbi:latest

$ singularity run ./casavlbi.pipe

Pipeline preparation (2/3)

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• $ cp -r /usr/local/src/picard/input_template/ input
• rPICARD will automatically identify and use files based on their extension

(freely configurable). Add files or links to workdir.�

• Raw visibility data
• FITS-IDI files or MS.�
• ANTAB a-priori calibration metadata�
• Text files containing flagging instructions for bad data�
• Other:
• Receiver temperatures, weather data, source models.

Configure (3/3)

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• input/observation.inp, input/array.inp
• Example:

##### observation.inp #####

science_target = 3C273, OJ287

calibrators_instrphase = 3C279

calibrators_bandpass = None

calibrators_rldly = None

calibrators_dterms = None

##### array.inp #####

array_type = GMVA

refant = LA, KP, PT

​

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Running the software

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​

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$ picard -p -n 4�

Inspect the data!!!

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jplotter: 3mm VLBA data of 3C279 & 3C273. Project code: S6096B (scan #14 & #1).

Amplitude calibration

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Accor & scalar bandpass (step 0, 1)

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7mm VLBA data of M87. Project code: BW0106.

Flux density calibration (step 2, 3)

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7mm VLBA data of M87. Project code: BW0106. T_sys ~ T_rx + (1 - e^-τ)T_atm → T_sys * e^τ_�

Phase calibration

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Intra-scan exhaustive fringe search

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7mm VLBA data of M87.

Project code: BW0106.

• A₀, B₀, C₀, D₀ list of prioritized reference stations.�
• Green : detection.�
• Red: Non-detection.�
• D₀ and d₁ still un-calibratable.�
• b₁, C₀, c_i calibratable via re-referencing.�

Solution interval estimation (step 4)

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7mm VLBA data of M87.

Project code: BW0106.

3mm VLBA data of 3C279. Project code: S6096B.

First: calibrator sources→solve instrumental effects��Then: weaker science targets

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Coherence calibration (step 5)

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7mm VLBA data of M87.

Project code: BW0106.

Some EHT data (1mm).

Atmospheric phase stabilization

========================>

Instrumental phases and delays (step 6)

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7mm VLBA data of M87.

Project code: BW0106.

Some EHT data (1mm).

Per-spw fringefit

============>

Complex bandpass (step 8)

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7mm VLBA data of M87.

Project code: BW0106.

7mm VLBA data of M87.

Project code: BW0106.

Now: All instrumental effects are taken out

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→ Calibrate science targets

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Last calibration steps: fringe-fit science targets

(steps 12, 13, 14)

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7mm VLBA data of M87.

Project code: BW0106.

• First: long integration (entire scan) to take out bulk delay or rate with maximized SNR.�→ Source detected or not?�Typically with open FFT search windows.�
• Then: Use narrow windows (small false detection probability) to solve for residual intra-scan atmospheric effects on short timescales.

→ Using optimized solution intervals.�

• Can also enable phase-referencing mode.
• Possibility for residual fringe search on sufficiently strong science targets.

Last calibration steps: fringe-fit science targets

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7mm VLBA data of M87.

Project code: BW0106.

7mm VLBA data of M87. Project code: BW0106.

THANKS TO OUR SPONSORS:

THIS EVENT HAS RECEIVED FUNDING FROM THE EUROPEAN UNION’S HORIZON 2020 RESEARCH AND INNOVATION PROGRAMME under grant agreements 730562 (RadioNet) and 7308844 (JUMPING JIVE)

CASA

Backup slides

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Pipeline installation

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• Get a test data set when not using your own:�$ wget https://ftp.science.ru.nl/astro/mjanssen/S6096B.tar.gz
• Using Singularity (for Docker see README) in the working dir:

$ singularity build casavlbi.pipe docker://mjanssen2308/casavlbi:latest

$ singularity run ./casavlbi.pipe

$ cp -r /usr/local/src/picard/input_template/ input

• From source for Ubuntu (Linux only, can have multiple CASA versions) in src dir:

$ git clone https://bitbucket.org/M_Janssen/picard

$ curl -L "$(cat picard/README.md | grep wget | cut -d' ' -f3)" -o CASA.picard.tar.xz

$ tar xJf CASA.picard.tar.xz && rm -rf CASA.picard.tar.xz

$ python picard/setup.py -a -p /usr/local/src

$ printf '\nexport PATH=$PATH:'"$(pwd)"'/picard/picard\n' >> ~/.bashrc

$ printf '\nexport PYTHONPATH=$PYTHONPATH:'"$(pwd)"'/picard/picard\n' >> ~/.bashrc

$ sudo apt-get install singularity-container� Or install https://github.com/haavee/jiveplot.

$ cd /path/to/working/dir && cp -r /path/to/picard/picard/input .

Running the software

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​

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• To run the full pipeline:�$ picard -p -n 4�
• Show command line arguments:�$ picard -h�
• Generate raw data visibility plots: $ picard -p -n 2 -q h,k

rPICARD steps

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Pre-calibration steps

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7mm VLBA data of M87.

Project code: BW0106.

1. Load data into MS, create obs summary file (listobs).�
2. Prepare flux density calibration metadata.�
3. Create and manage flag versions.�
4. Load source models.�
5. Flagging
1. Correlator (attached to FITS-IDI files).
2. Txt files.
3. Automated outlier detection in auto-correlations.
4. Edge channels.
5. Quack (scan start and end times).

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Solution interval estimation (step 5, 12)

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7mm VLBA data of M87.

Project code: BW0106.

• Fringe-fitting can be used to calibrate for intra-scan atmospheric effects on short timescales.�
• A source is detected when the SNR of the initial FFT is high enough.�The more detections per scan, the better the atmospheric calibration.�
• Input parameter: Search range depending on array sensitivity and observing frequency.�Set to ‘estimate’ by default.�
• For each scan, the solution interval which yields the most detections on all baselines is used.�
• Can calibrate sensitive baselines on short timescales and still get detections on longer timescales for baselines with weak signals.

→ Fringe-fit scans with 2 different solution intervals and merge calibration solutions.

Determine reference stations for global fringe-fit

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7mm VLBA data of M87.

Project code: BW0106.

• Two input parameters
• List of prioritized reference stations, e.g. EF, YS, MC, NT.
• Minimum fraction of valid (unflagged) data that must be present in a scan χ.
• For each scan, the first antenna in the refant list with�valid data > χ is picked as refant for that scan.
• If all valid data fractions < χ, the antenna with the most valid data is picked.�
• χ should be small for polarization experiments and/or when a single very sensitive station is present in the array (e.g., ALMA).�
• In the end all fringe solutions are re-referenced to one common antenna over the entire experiment to keep the R-L phase difference to a constant value from a single reference antenna.

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Multi-band calibrator fringe-fit & complex bandpass (steps 7, 8)

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7mm VLBA data of M87.

Project code: BW0106.

• After instrumental phase and delay offsets have been solved: Combine full band data for a fringe-fit to solve for atmospheric multi-band delays.

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• If SNR is good enough: Can combine all all calibrator data (SNR weighted) to fit for a complex (phase) bandpass.
• Per channel corrections or polynomial fit.

7mm VLBA data of M87. Project code: BW0106.

Polarization calibration (step 8, 9, 10)

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7mm VLBA data of M87.

Project code: BW0106.

• Solve for instrumental RL phase and delay offsets.��
• Simple CASA task available to solve for polarization leakage / D-terms.�
• More advanced task in development [IMV].
• Solve for non-linear effects.
• Handle varying polarized structure of extended sources.

Post-calibration steps

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7mm VLBA data of M87.

Project code: BW0106.

• Clear previous calibration.�
• Apply solution tables.�
• Print overview of flagged data percentages.�
• Make plots of visibilities.�
• Average (only channels by default) and export calibrated data.

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Calibration result

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7mm VLBA data of M87.

Project code: BW0106.

3mm VLBA data of 3C279. Project code: S6096B (scan #14).