Radio pulsar surveys with LOFAR Joeri van Leeuwen (ASTRON) + PWG 

Introduction 1 second of Crab-pulsar data with WSRT+PuMaII 

Galactic longitude (degrees) 270 -500 0 z (pc) 500 180 90 0 Why look for more pulsars? Young pulsars tell about birth location, velocities supernova mechanism Known proper motions of pulsars younger than 1Myr (Hobbs et al. 2005) 

12 13 11 -2 -1 0 1 Log period (s) Log magnetic field (G) Why look for more pulsars? Number of dim pulsars reveals supernova rates and minimum masses Clarify why long-period pulsars stop emitting Pulsar period versus magnetic field 

Why look for more pulsars? Pulsars 'time' the relativistic effects caused by a possible companion (neutron star / black hole) measures masses and spin pulse arrival time residual (µs) 

Why look with an interferometer? Time-based (vs. image-based) astronomy uses beam-forming, not interferometry Field of view dictated by largest separation, but sensitivity by total area: sparse Potentially form many parallel beams each with own periodicity-search back end Computationally challenging 8GR8; LOFAR; SKA (cf. Backer 1999) 

Why look with an interferometer? Beam-forming pulsar survey WSRT, at ~1000 beams First ever pulsars discovered from NL Can find ~10s of new pulsars 28 28.5 29 29.5 30 30.5 292 292.5 293 293.5 294 294.5 295 295.5 DEC (deg, J2000) R A (deg, J2000) 

LOFAR Pulsar survey Trade off between large FoV and high sensitivity. Supercore/core/entire LOFAR Different sparseness and total area 

LOFAR Pulsar survey Theoretical gains Core, coherent: 8.8 K/Jy Core+NL incoherent: 1.8 K/Jy Supercore: 2.9 K/Jy van Leeuwen & Stappers (2009) 

LOFAR Pulsar survey First station beam forming & tracking at Pulsar Busy Week Nov09: 

LOFAR Pulsar survey Theoretical gains Pointings for all-sky Core, coherent: 8.8 K/Jy 3.000.000 @ 2min Core+NL incoherent: 1.8 K/Jy 1.000 @ 1hr Supercore: 2.9 K/Jy van Leeuwen & Stappers (2009) 

LOFAR Pulsar survey Simulate birth rates, evolution, selection effects for 1e7 pulsars and 8 surveys: Survey Real Sim Jodrell (1972) 51 20 UMass-Arecibo (1974 50 39 MolongloII (1978) 224 227 UMass-NRAO (1978) 50 54 Parkes II (1991) 298 335 Cambr 80MHz (1993) 20 27 Parkes MB (1999) 1005 801 LOFAR (2009-2011) 

LOFAR Pulsar survey Simulate birth rates, evolution, selection effects for 1e7 pulsars and 8 surveys: Survey Real Sim Jodrell (1972) 51 20 UMass-Arecibo (1974 50 39 MolongloII (1978) 224 227 UMass-NRAO (1978) 50 54 Parkes II (1991) 298 335 Cambr 80MHz (1993) 20 27 Parkes MB (1999) 1005 801 LOFAR (2009-2011) 1200 

LOFAR Pulsar survey Relatively robust; different luminosity and gain models: 

LOFAR Pulsar survey Surveyed volume limited by multi-path scattering on ISM. van Leeuwen & Stappers (2009) 

LOFAR Pulsar survey Can however see all radio pulsars within ~2kpc -10 5 10 0 position (kpc) 15 -5 0 position (kpc) 5 10 Lofar detection Sun Galactic Centre -2 -1 position (kpc) 0 position (kpc) 2 1 -2 -1 0 2 1 

LOFAR Pulsar survey Can see very far out of galactic plane birth velocities: supernova kicks 

LOFAR Pulsar survey Measuring velocities, ages, magnetic fields, etc takes pulsar timing Initial positions: run incoherent beam forming + 10ms per second correlation in parallel Optimizing detected pulsars within station beam: 44% of pulsars are in pairs in station beam -- 20% in triples -- 19% in 4+ Coherent beamforming on those: 10hr total to get detection SNR on all sources 

Conclusions Computationally overcoming interferometer draw-backs (cf. SKA). Can find entire local population and measure velocity distribution infer supernova mass ranges, energetics