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LOFAR Tied-‐Array All Sky Survey
Searching for Pulsars with LOFAR
Sally Cooper The University of Manchester
+ LOFAR Pulsar Working Group
Pulsar Working Group Jason Hessels (co-‐lead) Ben Stappers (co-‐lead)
Anya Bilous Thijs Coenen Sally Cooper Heino Falcke
Jean-‐Mathias Griessmeier Tom Hassall
Aris Karastergiou Evan Keane
Vlad KondraFev Michael Kramer
Masaya Kuniyoshi Joeri van Leeuwen
Daniele Michilli Aris Noutsos Maura Pilia
Maciej Serylak CharloLe Sobey Sander ter Veen
Joris Verbiest Patrick Weltevrede
Kimon Zagkouris
ASTRON / Universiteit van Amsterdam University of Manchester Radboud Universiteit Nijmegen Universiteit van Amsterdam University of Manchester Radboud Universiteit Nijmegen LPC2E/CNRS University of Southampton University of Oxford MPI für Radioastronomie ASTRON MPI für Radioastronomie MPI für Radioastronomie ASTRON / Universiteit van Amsterdam ASTRON / Universiteit van Amsterdam MPI für Radioastronomie ASTRON University of Oxford MPI für Radioastronomie Radboud Universiteit Nijmegen MPI für Radioastronomie University of Manchester University of Oxford
Commissioning Surveys
7 incoherent staGon beams
75 square degrees FoV
57 minutes observaGons
LPPS 19 Ged array beams
4 square degrees FoV
17 minutes observaGons
LOTAS
Field of View SensiFvity
LOTAS Discoveries
J0140+5621 J0613+3731
LOTAS Discoveries
J0140+5621 J0613+3731
LOFAR Tied-‐Array All Sky Survey (LOTAAS)
§ Superterp HBA staGons § All Northern sky § 3 incoherent beams (SAP) § 67 Ged-‐array beams per SAP § 12 addiGonal TABs on known
sources § 119 – 151 MHz § 1 hour observaGons § 0.49 ms sampling Gme § 32 MHz bandwidth per SAP
LOTAAS Survey
Known pulsars
Tied-‐array beam Incoherent
beam
MulFple passes on sky: 3x with incoherent beams
1x full coverage Ged-‐array beams
Why LOTAAS?
• LOTAAS will be the deepest low-‐frequency pulsar survey ever done
• LOTAAS is expected to discover ~200 radio pulsars
• Characterise the local pulsar populaGon
• Variable sources and transients
• LOFAR/LOTAAS is a pathfinder for SKA pulsar surveys
Data Processing • 4TB for full poinGng (222 beams) • Originally processing in Manchester
(Hydra) – 90 nodes with 8 CPU’s – 15 hours to process single beam – 24 hours to process full poinGng
• Limited by downloading data
[Credit: Ant Holloway (JBCA)]
Cartesius • The Dutch naGonal supercomputer • Granted 10 million CPU hours • 500 nodes with 24 CPU’s
• 5 hours to process single beam • 5 hours to process full poinGng
(theoreGcal)
• Downloading data no longer boileneck • Stage data directly from Grid to Cartesius • Download full poinGng in 7 hours (simultaneous downloads)
Current Status
• 270 observed poinGngs out of the 650 in Pass A
• Processed 160 poinGngs • Period and single pulse searching
• 3 million candidates • Viewing candidates by eye • 65 known pulsar redetecGons
Candidate plot with known pulsar detecGon
Pulsar Discoveries
J1529+40 P = 0.476 s DM = 6.6 σ = 13.6
J0935+33 P = 0.961 s DM = 18.4 σ = 19.6
J2350+31 P = 0.508 s DM = 39.1 σ = 33.8
J1809+17 P = 2.066 s DM = 47.0 σ = 9.3
ConfirmaGon
• Full LOFAR core • 127 beams • 15 or 30 min observaGons
Machine Learning • 3 million candidates • Too many to visually inspect
• Machine learning algorithm • Scoring system to represent candidates
Data
Classifier
Training Set
PredicGons
• 22 scores: Period, SNR, DM, peaks in profile etc. • Neural network
Ø Successful for HTRU • Applied same HTRU classifier to LOTAAS candidates
Ø Unsuccessful. Failed to return discovery pulsars. High false posiGve rate
Very Fast Decision Tree
• Need LOFAR specific training set of known pulsars Ø 65 known pulsars including 4 LOTAAS discoveries
• Update scoring system Ø Rob Lyon Ø 8 scores based on only the staGsGcs of the pulse
profile and the DM curve • Very Fast Decision Tree Algorithm Classifier
Ø Applied to all 3 million candidates Ø 8300 posiGve predicGons Ø RedetecGon of known pulsars: 80 Ø 5 new discoveries
Pulsar Discoveries
J1814+22 P = 0.253 DM62.3 σ = 11.8
J2336-‐01 P = 1.029 s DM =19.6 σ = 31.5
J2057+21 P = 1.116 s DM = 73.6 σ = 5.8
J0305+11 P = 0.862 DM = 27.8 σ = 8.9
J0317+13 P = 1.974 DM = 12.9 σ = 17.6
J2350+31 J0317+13
J2057+21 J0613+37 J0140+56
J0935+33
J1529+40
J1809+17
J2336-01
J0305+11
J0317+13
J2057+21 J0613+37 J0140+56
J0935+33
J1529+40
J1809+17
J2336-01
J0305+11 J1814+22 J2350+31
Completed PoinGngs Incoherent beams
LOTAAS pulsars LOTAS pulsars Tied-‐array
beams
GBNCC independent discoveries
J0216+52 J1815+55 J1800+50 J2001+42
SensiGvity
• Known pulsars ² Discovery
Minimum theoreGcal flux of Superterp at DM = 50 and 300 cm3 pc for low and high galacGc laGtudes
Period short 0.065 s
Period long 3.033 s
DM low 2.96 cm3 pc
DM high 171.73 cm3 pc
Tsys dominated by Tsky Bhat 2004 scaiering
Lovell ObservaGons
J1529+4049
J0613+3734
J0140+56
InternaGonal StaGons Nançay
J2350+31 2 hours
113 MHz 138 MHz
161 MHz 185 MHz
Conclusions
• 3 million candidates • skimmed the surface • Machine learning
– original score system has been revised – 80+ known pulsars
• 11 new pulsar discoveries (9 + 2) • Analyse single pulse search output: Daniele Michilli • Timing with LOFAR, Lovell at 1.4 GHz and Int’l staGons • Long term proposal submiied/accepted for 1001 hours Discovery webpage hip://www.astron.nl/lotaas