Archival Radio Transients and the LOFAR Transient Pipeline

1
Archival Radio Transients and the LOFAR Transient
Pipeline
Martin Bell Rob Fender Southampton University
2
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
Previous testing
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
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
4
Previous testing
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
J18193845-12 Epochs of (full synthesis) WSRT
data of the scintillating Quasar
J18193854.(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
5
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.
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
SubmilliJansky Transients in Archival Radio
Observations, Bower et al 2007
Bower Deep Field
Single Epoch Example
6
Flux and Phase Calibration Fields
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
-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 glanceTOTAL 5418 Images
7
Parseltongue Pipeline Procedure
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
Iterate
PHASE Normal Calib
Raw Data
Search for Flux or Phase Calibrator
Self cal
Remove Calibrator
Image
FLUX Model Calib
Ignore target Data
TRY
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.
8
Source Removal and Example Pipeline Image
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

• Improve Dynamic range by modelling and removing
  central calibrator.-Improve noise using
  selfcal.-Noise Measured 441µJy/Beam-Noise
  Theoretical 120µJy/Beam

Un-removed
Removed

• Dynamic range 122901

3C48 Off
3C48 Off

• Integration time 3.5 mins-3C48 FLux
  5.42Jy

3C48
9
Database Interaction and Visualisation
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
-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
10
Possible Candidates RT 1986-01-06 (3C48 Field)
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

• 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

3C48 Off
3C48 Off
11
Possible Candidates RT 1995-04-18 (3C48 Field)
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

• 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

2x Half Power Radius
3C48 Off
12
Log N Log S and Expected Rate
VLA
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
-Calculate expected detection rate using
Bower results over the whole sky.
-3
-4
13
Log N Log S and Expected Rate
VLA
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
-Calculate expected detection rate using
Bower results over the whole sky
-3
-4
LOFAR Whole Sky
14
Conclusions
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
-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)
Thank You
15
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