LOFAR for Pulsars

Ben StappersJBCA, 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 FoVbut LOFAR is a sparse array!

M = N * FoV * (A/T)2 * BW * (-1.8)2

Dcore = 2 km, Dstation = 30 m< 25 stations in the core

NCTA > 22 (50/E) (15/rstation)2 (rcore/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 2001Deshpande & 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

• Aeff 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 Tsky 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

Tscatt = 5.2X10-7 DM3.8 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 LOFARcould 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 L1400 > 1 mJy kpc2 (not SNR PSRs)If L limit exists similar to that of Lyne et al of L400 = 1 mJy kpc2 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

• J0218+4232 already scattered at 250 MHz

• No clear indication why others not seen (flux/scatt)

• B1957+20 detected, worst DM/P combination

J0034-0534 vs J1713+0747• P= 0.0045701365227338• DM = 15.992• = 0.12 ms (150MHz)

• = 28 ms (116MHz)measured

• Not seen from 100-170 MHz

• P= 0.0018771818543796• DM = 13.763• = 0.06 ms (150MHz)

• = 0.05 ms (116 MHz)measured

NE2001NE2001

Profile EvolutionPSR J1022+1001 PSR J2145-0750

PSR B1257+12 PSR J1744-1134 PSR J1911-1114

see and cf. KL99, KL01 and KL96

Strong component evolution but little evolution of width with frequency

Extragalactic pulsarsLOFAR will be sensitive to normal andgiant pulse emission from nearby galaxies.

•In M33, 10 hour obsn can detect pulsars with L> 57 Jy kpc2 , 10 pulsars known

•Brightest could be obs’d out to 1.2 Mpc

•Depending on SI can detect GPs out to 2- 4.5 Mpc

van Leeuwen & Stappers 2007

Crab Giant Pulse observed withthe WSRT LFFEs at 141 MHz. LOFAR will have atLeast 30 times sensitivity, 12 times BW

The All-sky monitor: Transients

ASM will make images of skyon logarithmically spacedIntervals from 1s to 1000s

Dedicated mode in both LBAAnd HBA can see almost all ofCE beam, thus LARGE piece of SKY!

Other times will piggy back usingavailable 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 frequencysimultaneity 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. obs @ high freqs.) PSRs B1133+16 and 2016+28 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 B1855+09

scatt~ 0.00005 s Single pulses SNR~12

Plasma and the ISM

A dynamic and secondary spectra for PSR B0834+06 showing the influence of ~1 AU size structures in the ISM with electron densities of ~200. Hill et al. 2005

• 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 J0034-0534 1.8 ms/DM 13

141 MHz. LOFAR will have at least 12 times sensitivity

Single Pulses B0329+54

Profiles at 3 different frequencies. Some evidence forscattering at 130 MHz but excellent SNR!

B0950+08

Frequency

Time

116 MHz

163 MHz

Scintillation B0950+08

First pulsar detection with LOFAR• PSR B0329+54 for 15 min.

• 48 X 0.15625 kHz subbands

• 170-230 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 for1.3s or 200 kHz BW for 650sor 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 fieldIt will also reveal things we haven’t even thought of !!!!