Archival radio transients and the LOFAR transient pipeline.

Martin Bell
LOFAR and the Transient Radio Sky, Amsterdam, December 2008

Transcript

1. 16th December 2008 LOFAR and the Transient Radio Sky Workshop: Martin Bell Archival Radio Transients and the LOFAR Transient Pipeline Martin Bell Rob Fender Southampton University
2. 16th December 2008 LOFAR and the Transient Radio Sky Workshop: Martin Bell Introduction Goals of this Work 1.To test the functionality of LOFAR source extraction and transient detection algorithms prior to commissioning. 2. To find, classify and interpret the underlying physics of previously undiscovered archival radio transients. 3.To use archival transients to constrain the predicted detection rate of new transients excepted with LOFAR. Hopefully providing testable a priori information about the transient LOFAR sky. 1 Contents 2 Intro 3 Previous Testing 4 Calib Fields 5 Pipeline 6 Source Removal 7 Progress 8 Visual Aids 9 Results 10 Rate 11 Finish
3. 16th December 2008 LOFAR and the Transient Radio Sky Workshop: Martin Bell Previous testing NGC 7213 -Two years of monitoring of the Low Luminosity AGN NGC 7213 with ATCA. -Light curve comparison between MIRIAD Gaussian fit and LOFAR pipeline fitting routines. -Good Agreement Found 8.4GHz 1 Contents 2 Intro 3 Previous Testing 4 Calib Fields 5 Pipeline 6 Source Removal 7 Progress 8 Visual Aids 9 Results 10 Rate 11 Finish
4. 16th December 2008 LOFAR and the Transient Radio Sky Workshop: Martin Bell Previous testing J1819+3845 -12 Epochs of (full synthesis) WSRT data of the scintillating Quasar J1819+3854. (J.Dennett-Thorpe and A.G.de Bruyn 2003) -Used to check source extraction and transient trigger thresholds. -Used to develop database visualisation and interaction tools. Courtesy of De Bruyn et al 1 Contents 2 Intro 3 Previous Testing 4 Calib Fields 5 Pipeline 6 Source Removal 7 Progress 8 Visual Aids 9 Results 10 Rate 11 Finish
5. 16th December 2008 LOFAR and the Transient Radio Sky Workshop: Martin Bell Previous testing Bower Field -Archival VLA data of approx 800 Epochs (C Band) found 7 radio transients. -Parseltongue pipeline procedure written to reduce VLA data and reproduce Bower transient results. SubmilliJansky Transients in Archival Radio Observations, Bower et al 2007 Bower Deep Field Single Epoch Example 1 Contents 2 Intro 3 Previous Testing 4 Calib Fields 5 Pipeline 6 Source Removal 7 Progress 8 Visual Aids 9 Results 10 Rate 11 Finish
6. 16th December 2008 LOFAR and the Transient Radio Sky Workshop: Martin Bell Flux and Phase Calibration Fields “System” “Point” “BOWER” “Base” “Ops”,”Sys” Calibrator Number Observations 3C48 850 3C286 1206 0508+788 805 1928+738 1008 1741-038 766 2022-616 783 -What is the most observed field at the VLA? -Difficult to perform a ‘blind' search in VLA archive, can perform a project search. At a glance TOTAL = 5418 Images 1 Contents 2 Intro 3 Previous Testing 4 Calib Fields 5 Pipeline 6 Source Removal 7 Progress 8 Visual Aids 9 Results 10 Rate 11 Finish
7. 16th December 2008 LOFAR and the Transient Radio Sky Workshop: Martin Bell Parseltongue Pipeline Procedure Raw Data Search for Flux or Phase Calibrator Ignore target Data FLUX Model Calib PHASE Normal Calib Self cal Remove Calibrator Image TRY Iterate Script: -Image any calibrator recognised by the VLA. -Create as many usable calibrator field images as possible and perform transient search. -Re-process data with different calibration settings to maximise success rate of reduction script. 1 Contents 2 Intro 3 Previous Testing 4 Calib Fields 5 Pipeline 6 Source Removal 7 Progress 8 Visual Aids 9 Results 10 Rate 11 Finish
8. 16th December 2008 LOFAR and the Transient Radio Sky Workshop: Martin Bell Source Removal and Example Pipeline Image 3C48 - Improve Dynamic range by modelling and removing central calibrator. -Improve noise using selfcal. -Noise Measured = 441µJy/Beam -Noise Theoretical = 120µJy/Beam - Dynamic range = 12290:1 - Integration time = 3.5 mins -3C48 FLux = 5.42Jy Un-removed Removed 3C48 Off 3C48 Off 1 Contents 2 Intro 3 Previous Testing 4 Calib Fields 5 Pipeline 6 Source Removal 7 Progress 8 Visual Aids 9 Results 10 Rate 11 Finish
9. 16th December 2008 LOFAR and the Transient Radio Sky Workshop: Martin Bell Database Interaction and Visualisation -GUI written to ease querying of database. -Could be path finder for more generic database interaction tool needed to intelligently query transient archive. -Primarily written for my own work -Nest appropriate ‘MySQL’ commands into python GUI to display images, identify sources and produce light curves. J1819 Images Courtesy of De Bruyn et al 1 Contents 2 Intro 3 Previous Testing 4 Calib Fields 5 Pipeline 6 Source Removal 7 Progress 8 Visual Aids 9 Results 10 Rate 11 Finish
10. 16th December 2008 LOFAR and the Transient Radio Sky Workshop: Martin Bell Possible Candidates RT 1986-01-06 (3C48 Field) - Disclaimer: -Integration time only 1 minute!!! -This could be a real transient or ‘cleaned’ artefact from the diffraction pattern. Analysis or raw data is in-conclusive. -HOWEVER We should find a lot of ‘Candidates’ then look at raw data to ascertain reproducibility 9.4 14 Detection!! v S mJy σ = 3C48 Off 3C48 Off 1 Contents 2 Intro 3 Previous Testing 4 Calib Fields 5 Pipeline 6 Source Removal 7 Progress 8 Visual Aids 9 Results 10 Rate 11 Finish
11. 16th December 2008 LOFAR and the Transient Radio Sky Workshop: Martin Bell Possible Candidates RT 1995-04-18 (3C48 Field) - Disclaimer: -Integration time only 1.5 minutes!!! -This could be a real transient or ‘cleaned’ artefact from the diffraction pattern. Analysis or raw data is in-conclusive. -HOWEVER We should find a lot of ‘Candidates’ then look at raw data to ascertain reproducibility 3C48 Off 7.19 v S mJy = 2x Half Power Radius 1 Contents 2 Intro 3 Previous Testing 4 Calib Fields 5 Pipeline 6 Source Removal 7 Progress 8 Visual Aids 9 Results 10 Rate 11 Finish
12. 16th December 2008 LOFAR and the Transient Radio Sky Workshop: Martin Bell Log N Log S and Expected Rate 1 Contents 2 Intro 3 Previous Testing 4 Calib Fields 5 Pipeline 6 Source Removal 7 Progress 8 Visual Aids 9 Results 10 Rate 11 Finish VLA 2 1 ( deg ) Log N s − − ( ) v Log S -3 -4 -Calculate expected detection rate using Bower results over the whole sky.
13. 16th December 2008 LOFAR and the Transient Radio Sky Workshop: Martin Bell Log N Log S and Expected Rate 1 Contents 2 Intro 3 Previous Testing 4 Calib Fields 5 Pipeline 6 Source Removal 7 Progress 8 Visual Aids 9 Results 10 Rate 11 Finish VLA 2 1 ( deg ) Log N s − − ( ) v Log S -3 -4 -Calculate expected detection rate using Bower results over the whole sky LOFAR Whole Sky 5 1 9 1 4.5 10 2.4 10 yr R yr − − × ≤ ≥ ×
14. 16th December 2008 LOFAR and the Transient Radio Sky Workshop: Martin Bell Conclusions -IN SUMMARY: We want to image ALL usable calibration and target fields observed with the VLA. -Try and ‘close the book’ as much as possible on pre LOFAR era radio transients. -Constrain statistics on rate of radio transients. -Test LOFAR transient detection algorithms. -Any suggestions for commonly observed fields? -Use other arrays to image calibrators (WSRT,ATCA,GMRT) 1 Contents 2 Intro 3 Previous Testing 4 Calib Fields 5 Pipeline 6 Source Removal 7 Progress 8 Visual Aids 9 Results 10 Rate 11 Finish Thank You
15. 16th December 2008 LOFAR and the Transient Radio Sky Workshop: Martin Bell Contents 1 Contents 2 Intro 3 Previous Testing 4 Calib Fields 5 Pipeline 6 Source Removal 7 Progress 8 Visual Aids 9 Results 10 Rate 11 Finish