1. MWA imaging and calibration – early science results
Nadia Kudryavtseva, Stiven Tingay,
Randall Wayth, David Kaplan, Aziz Jiwani
Curtin University of Technology
Australia

2. Outline
MWA calibration challenge – list of problems which should be corrected
Current status of calibration
What will change with 128T compare to 512T?
Future prospects

3. MWA calibration challenge
Big field of view
Large bandwidth
Direction dependency
Ionosphere

4. MWA calibration challenge
Interstellar
medium
Ionosphere
Correlated
beam
All changing with time and position in the sky
Tile beam

5. Phases Ionosphere Large field Of view calibration Pointing error
Correct using known positions of calibrators
GPS station?
Ionosphere
Large field
Of view
calibration
Fasceting imaging, multiple calibrators
In the field of view
Pointing
error
Calculating known offset and correcting
For it in the beginning of calibration

6. Amplitudes Ionosphere? Pointing error Tile beam Correlated Correlated
Very difficult task. Requires ionospheric modelling
Ionosphere?
Large field
Of view
calibration
Fasceting imaging, multiple calibrators
In the field of view
Pointing
error
Requires knowledge of correlated beam
Pattern and tile beam pattern
Tile beam
Direction dependent, known sources,
Theoretical beam, two calibrators in the field
Correlated
beam
Correlated
beam
Direction dependent, theoretical model?
Bandpass
Correlated
beam
Calibration using peeled calibrator
Corrected ripples in bandpass using known
Sources
Sources
In sidelobes
Correlated
beam
Peeling off sources

7. PicA field

8. Ionosphere Compared positions with SUMMS catalogue
Y [deg]
X [deg]
Compared positions with SUMMS catalogue
degrees offset

9. Tile beam

10. Tile beam
Direction dependent and frequency-dependent
Tile sensitivity

11. Tile beam

12. Tile beam Tile beam from PicA observations Flux difference [Jy]
X [deg]
Tile beam from PicA observations

13. Sources in sidelobes Noise from sources in sidelobes
→ Changing on a timescale of 5 mins

14. Correlated beam
Dirty beam from miriad

15. Bandpass

16. Bandpass

17. Tile beam

18. Variability

19. Variability

20. Tile beam

21. Self-calibration

22. Quasar variability

23. 128T vs 512T
8 times less transient detections with 128T
R ~S-3/2 (Macquart 2011)

24. Conclusions
1. RFI is less than 2 percents
2. Bandpass correction – much better when peeling off the calibrator source
3. Bandpass is stable over 1 hour
4. Self-calibration does not help
5. We need to understand tile and correlated beam
6. With current understanding of the beams it 6-10% error in calibrators' flux-densities

25. Future work 1. Understanding tile beam:
- Map two calibrators in the field
- Drift scans
- Measure dipole beam and reconstruct the tile beam
- Scanning with emitting antenna?
2. Understanding correlated beam:
- find correlated noise
- use model based on tile beam
3. Subtracting the data:
- useful for transient science
4. Imaging: Change FFT to Fast Wavelet Transform

26. Tile beam