• Updates to Strategy – Quality Control – Peeling • Current Image Examples • Transient Searching • Conclusions/Future Work 03/12/2012 Searching for Transients at the NCP – Amsterdam LOFAR TKP Mee0ng 2
Sky Survey. • With each MSSS-‐LBA observa0on, a single sub band was placed on the NCP field. 60 MHz observa0ons with ~200 kHz bandwidth with 100 deg2 FoV. • 2606, 11 minute, snapshots. 03/12/2012 3 Searching for Transients at the NCP – Amsterdam LOFAR TKP Mee0ng • Observed December 2011 – April 2012 (~80% complete). • MSSS LBA s0ll at 80% observed – so a few more NCP observa0ons to come. msss.astron.nl
reduc0on strategy. • Features such as: – Automa0cally flag bad sta0ons. – Automa0cally clip bad amplitude gains in calibrators. – Provides diagnos0c plots of results during processing. • Refer to MSSS reports page on the wiki 03/12/2012 Searching for Transients at the NCP – Amsterdam LOFAR TKP Mee0ng 4 Simultaneously observe calibrator Transfer gain solu0ons to target from calibrator Perform phase only calibra0on using model Image
are simply bad… • Agempted to create a non-‐imaging method to detect bad data. • Read the visibili0es from each processed dataset looking at the mean or median values. 03/12/2012 Searching for Transients at the NCP – Amsterdam LOFAR TKP Mee0ng 5 L49040 (2012-‐02-‐27 04:13:00)
method of cukng very bad observa0ons. • However, could not rely on method completely, and this combined with imaging each observa0on gave us a final ‘bad list’. 03/12/2012 Searching for Transients at the NCP – Amsterdam LOFAR TKP Mee0ng 6 Missing sta0ons Seems to be odd cases of rfi or poor calibra0on.
calibrator observa0ons to check performance. • Calibrators seemed to show a slight rise in flux depending on their eleva0on in the sky. • When the beam correc0on is completely turned off in BBS – the rise disappears. • Suggests an error with the beam model?.. Ongoing. 03/12/2012 Searching for Transients at the NCP – Amsterdam LOFAR TKP Mee0ng 7
technique developed by Mike Bell for MSSS. – See Week 26 MSSS report for more details • While improving quality – the method has also been used to subtract 3C 61.1. • Agemp0ng to also peel the next brightest source, 3C 220.3 , however had issues… 03/12/2012 Searching for Transients at the NCP – Amsterdam LOFAR TKP Mee0ng 8 Subtract ALL sources, add back those to be peeled Solve for DDGs in the direc0on of the sources Subtract peeled sources and apply solu0ons Add back all unpeeled sources and perform phase only calibra0on
data in a single sub band for BBS to solve. • While some0mes it was successful, in others chunks of data would be flagged. • Hence only 3C 61.1 is used for peeling. 03/12/2012 Searching for Transients at the NCP – Amsterdam LOFAR TKP Mee0ng 9 Before Peeling Aqer Peeling Very slight noise improvement
observa0ons has a different Right Ascension. – Has the effect of making the produced maps rotate. • Processed one set of data where the phase center has been manually set using NDPPP. • Enables making different combina0ons much simpler. 03/12/2012 Searching for Transients at the NCP – Amsterdam LOFAR TKP Mee0ng 10 Double 3C 61.1
Awimager – Thanks to Cyril Tasse • Speed of imaging the NCP has drama0cally improved. • For example, a concatenated 50 observa0on dataset, imaging size of 1024, 40 arcsec cell size, deep cleaning, on 12 core Southampton LOFAR machine: • Some0mes can s0ll use very small major clean cycles, thus taking a long 0me – usually bad data. 03/12/2012 Searching for Transients at the NCP – Amsterdam LOFAR TKP Mee0ng 11 Old AWimager New AWimager Average Memory Usage ~25 GB ~3 GB Time Taken 11:58:27 00:08:31
follow a √N improvement? • Shows noise improvement from concatena0ng 8, 16, 24, 32, 40 and 50 observa0ons. • Can also combine in the image plane, using the 50 SB images – not ideal method. 03/12/2012 Searching for Transients at the NCP – Amsterdam LOFAR TKP Mee0ng 16
it should be – concentra0on going forward on transient searching. • Search in early stages – however can begin to think about what limits would be imposed considering different groupings. • NCP observa0ons slightly sporadic – groupings need to be thought about carefully. 03/12/2012 Searching for Transients at the NCP – Amsterdam LOFAR TKP Mee0ng 17
the main tool for analysis. • Light Curves, source posi0ons etc. • Data processed in August, imaged with CASA, was partly passed through – no transients. • Image sets are ready to be passed through. 03/12/2012 Searching for Transients at the NCP – Amsterdam LOFAR TKP Mee0ng 19
state – any addi0ons would be small improvements – closely monitor MSSS. • Producing very nice maps, especially with the new AWimager. • Huge poten0al for transient searching, is now really the main focus in the immediate future. • Dataset also proved to be useful simply in terms of LOFAR commissioning/MSSS • Next steps: – Find transients (?) – NCP Field hopefully con0nued to be monitored. 03/12/2012 Searching for Transients at the NCP – Amsterdam LOFAR TKP Mee0ng 20