LOFAR for Pulsars Ben Stappers JBCA, Manchester

Outline:  LOFAR: briefly what we need from LOFAR  Pros and cons of low-frequency observations  How to find new pulsars with LOFAR  How many pulsars will we find?  What about Millisecond Pulsars?  Transient “pulsars” and how to catch them  Studying individual Pulsars  First Pulsar with LOFAR  Conclusions

Pulsar Survey with LOFAR: The Challenge Need to maximise FoV but LOFAR is a sparse array! M = N * FoV * (A/T) 2 * BW * ( -1.8 ) 2 D core = 2 km, D station = 30 m < 25 stations in the core N CTA > 22 (50/E) (15/r station ) 2 (r core /1000) 2 SOLUTION: Either add telescopes incoherently or have many TABs BUT: at least 35 times more data throughput and signal processing. On the other hand: It does give significantly better positions. Due to shorter integrations required also possibly less total resources Sensitivity scales as:

The Spectra Kuzmin & Losovsky 2001 Deshpande & Radhakrishnan 1992 (34.5 MHz data) Maron et al 2000 Typical pulsar spectra When 34 MHz data incl. MSP spectra, no turnover?

Pulsar Survey with LOFAR: Optimal Freq. Max(M = N * FoV * (A/T) 2 * BW * ( -  ) 2 ) FoV scales as 2 A eff scales as -2 above 140 MHz and 2 below Pulsar flux scales (on avg) as -1.5 (i.e.  = -1.5) T should be dominated by T sky and it scales as -2.6 Extra considerations for: Dispersion increases as we go to lower but we can correct for it. Scattering is the biggest problem -4.4 limits distance to which detect pulsars T scatt = 5.2 X DM 3.8 s at 140 MHz van leeuwen & Stappers 2007

Pulsar Survey with LOFAR:How Many? Model Parameters all from previous page model of pulsar luminosity (v. impt) model of birth periods & sky distribution sky seen from LOFAR in NL location dependent sensitivity of LOFAR With 60 minute pointings LOFAR could detect at least 1000 new pulsars in the Northern sky in just 60 days of observing. Survey time reduced if more Beams are available In the core. Depend. on lum fn. longer pointings not necc. more PSRs found. If use TABs pointings shorter. More than 22 TABs = survey faster or can get back some of lost sensitivity. 90% efficient 100% efficient 12 sigma, 50*24 tile stations, 80% of 32 MHz

Pulsar Survey with LOFAR: Where? Pulsars detected are mainly nearby due to scattering! Lorimer et al 2006: model PMB pulsars =>80% pulsars have L 1400 > 1 mJy kpc 2 (not SNR PSRs) If L limit exists similar to that of Lyne et al of L 400 = 1 mJy kpc 2 then LOFAR will see ALL pulsars beamed in our direction out to d = 1.4 kpc! Alternatively LOFAR will probe the limit of the luminosity function in great detail! Constraining the dN/dL is vital for knowing how many radio pulsars/NSs there are.

A full census of radio emitting NSs! Sources apparently seen at low frequencies Geminga like pulsars AXPs/SGRs Pulsars that are brighter at low frequencies Steep spectrum (>-3,B0943) nearby MSPs (unbroken spectra) Long pointings mean sensitive to more transient NSs RRATs (long pointings, low-DM) Sometimes a pulsar sources (on 10%) Radio emitting magnetars Along with “normal” pulsars sensitive to:

Results 9/16 MSPs were detected J already scattered at 250 MHz No clear indication why others not seen (flux/scatt) B detected, worst DM/P combination

J vs J P= DM =  = 0.12 ms (150MHz)  = 28 ms (116MHz) measured Not seen from MHz P= DM =  = 0.06 ms (150MHz)  = 0.05 ms (116 MHz) measured NE2001

Profile Evolution PSR J PSR J PSR B PSR J PSR J see and cf. KL99, KL01 and KL96 Strong component evolution but little evolution of width with frequency

Extragalactic pulsars LOFAR will be sensitive to normal and giant pulse emission from nearby galaxies. In M33, 10 hour obsn can detect pulsars with L> 57 Jy kpc 2, 10 pulsars known Brightest could be obs’d out to 1.2 Mpc Depending on SI can detect GPs out to Mpc van Leeuwen & Stappers 2007 Crab Giant Pulse observed with the WSRT LFFEs at 141 MHz. LOFAR will have at Least 30 times sensitivity, 12 times BW

The All-sky monitor: Transients ASM will make images of sky on logarithmically spaced Intervals from 1s to 1000s Dedicated mode in both LBA And HBA can see almost all of CE beam, thus LARGE piece of SKY! Other times will piggy back using available resources. Instant alerting system available to community. RRATs bright enough to see Nullers still show flux var. AXP/Magnetars long periods! GCRT-like sources long P also 1s relatively long for NSs, BUT:

Spectra over full LOFAR range simultaneously (30-240). need multiple telescopes to do at high frequency simultaneity important due to scint. Etc…. Important physics in break/non-break with regard to emission mech. Large sample, check stats, e.g.  &  Do MSP spectra, really show less turnover Checks of RFM, aberration, retardation? Simult. wide frequency obs, DM variations Polarisation Profile evolution (incl. high freqs.) PSRs B and showing Std. RFM and non-std RFM. Izvekova etal 1993 Sensitive! 1/4 PSRs HB, 1/5 PSRs LB Plasma dynamics: -struct, drifting Polarisation, simult with HFs. Single pulses from MSPs! => Nulling/Moding/Drifting Pulsar Emission Physics PSR B  scatt ~ s Single pulses SNR~12

Plasma and the ISM A dynamic and secondary spectra for PSR B showing the influence of ~1 AU size structures in the ISM with electron densities of ~200. Hill et al Study local ISM via DS & SS Can monitor these variations Excellent probe of local electron density via large number of PSRs Unique studies of scattering RMs will be measurable -- B gal. Can also be used to study these properties of the e-gal pulsars. Dispersion & Rotation Measure in the magnetosphere Refraction effects Comparison of scattering to HI regions Lohmer et al.

LFFE MSP J ms/DM MHz. LOFAR will have at least 12 times sensitivity Single Pulses B Profiles at 3 different frequencies. Some evidence for scattering at 130 MHz but excellent SNR! B Frequency Time 116 MHz 163 MHz Scintillation B

First pulsar detection with LOFAR PSR B for 15 min. 48 X kHz subbands MHz 6 HBA tiles Approx 0.2% of LOFAR sensitivity for pulsar work LOFAR will almost double total pulsar population (Poster 15S)

Exceptional sensitivity combined with the multi-beam capabilities make LOFAR useful for monitoring programs. Regular timing to catch Glitches Regular timing to provide solutions for gravitational wave observatories and GLAST Catch transitions of “more off than on” pulsars The radio-sky monitor will find new transient pulsar sources but will also allow rapid follow-up and via the TBB a look back in time at the event itself. TBB can store 100 MHz BW for 1.3s or 200 kHz BW for 650s or anything in between. Some other possibilities

Conclusions LOFAR will find at least 1000 “normal” pulsars If there is a popn. of steep spectrum pulsars it will be more Long pointings mean it will also find “transient” pulsars A complete census of the local NS population The ASM will also reveal many more transient RNSs The raw sensitivity of LOFAR will enable many studies related to how RNSs emit (single pulses, spectra, poln) It will also provide an excellent probe of the local ISM both the local electron density and magnetic field It will also reveal things we haven’t even thought of !!!!