LOFAR for Pulsar. Ben Stappers ASTRON/UvA

Transcription

1 LOFAR for Pulsar Ben Stappers ASTRON/UvA

2 Outline: LOFAR a short introduction Pros and cons of low-frequency observation How to find new pulsars with LOFAR Studying individual Pulsars average pulse profiles spectra single pulses ISM polarisation LFFEs & CS 1 results Conclusions

3 LOFAR: The Basics Telescope the size of the Netherlands with extension to Germany, UK, France, Frequencies: (10)30-240(270) MHz Wavelengths: 10m m Square Kilometer Array (SKA) prototype at lowfrequencies Interferometer baselines: 100 km European Expansion to 1000 km Aperture array: Replace big dishes by many cheap dipoles 77 Dutch stations of 96 dipole antennas + extra sensors (geo+meteo) ~ 20 European stations No movin g parts: electronic beam steering Supercomputer synthesizes giant dish Two orders of magnitude improvement in resolution and sensitivity Instantaneous view of almost entire sky Multibeaming capability (8 beams/24 beams) >20 Tbit/sec raw data >40 Tflop supercomputer Large data rates in all modes but especially pulsar mode.

4 LOFAR: The Basics II Stations: 96 Low Band Antenna s Distributed over ~60 m Optimized for MHz 96 High Band Tiles 4x4 antenna s Distributed over ~50m Optimized ~ MHz Full Array: 77 Stations Diameter about 100 km 32 MHz BW * beams 12 bit 8 * 4 MHz beams possible Tied Array maybe to first ring Core: 32 Stations Diameter about 2.5 km 32 MHz BW * beams 12 bit 8 * 4 MHz beams possible Tied Array Phase II 24 beams 32 MHz BW 4 bits

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

6 Freq (MHz) The ISM (Con & Pro) Dispersion: SOLUTION: T Coherent ν -2 dedispersion uses a filter which can exactly correct for the passage through the ISM BUT: BW 32 (MHz) s 0.98 s 0.049s 25i) Computationally 1700s 212.7s 10.6s very expensive ii) Never done for large scale pulsar survey Scattering: iii) Very large data sets (T res > 5 µs,164 Channels) ISM BW 4 (MHz) observed intensity intrinsic profile BW 200 (khz) > 506*N TAB MB/s New y(t) algorithms = I(t) h(t) necessary, possible (coherently) dedisperse the streaming data! ISM impulse response function 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. 2005

7 Pulsar Survey with LOFAR: The Cha Sensitivity scales as: M = N * FoV * (A/T) 2 * BW * (ν -1.8 ) 2 Need to maximise FoV but LOFAR is a sparse array! D core = 2 km, D station = 60 m 32 stations in the core N CTA > 35 (32/E) (60/r station ) 2 (r core /2000) 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.

8 The All-sky monitor: Transien 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! Other times will piggy back using available resources. 1s relatively long for N RRATs bright enough to Instant alerting system available see to community. Nullers still show flux var. AXP/Magnetars long

9 Pulsar Emission Physics 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. α & β Do MSP spectra, really show less turnover Sensitive! 1/3 PSRs HB, 1/4 PSRs LB Plasma dynamics: µ-struct, drifting Polarisation, simult with HFs. Single pulses from MSPs! => Nulling/Moding/Drifting PSR B τ scatt ~ s Single pulses SNR~20 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

10 Plasma and the ISM Dispersion & Rotation Measure in the magnetosphere Refraction effects 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. Comparison of scattering to HI regions Lohmer et al.

11 LFFE MSP J ms/dm 13 Single Pulses B Profiles at 3 different frequencies. Some evidence for scattering at 130 MHz but excellent SNR! 141 MHz. LOFAR will have at Least 30 times sensitivity, 12 times BW

12 CS1 CS008 CS010 CS001 CS016 Station in Effelsberg had FL, end 2007 in Potsdam, Next year likely 3-4 in UK + more in Germany/Franc

13 CS1

14 Some other possibilities 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.

15 Once add Single pulse search/ffa/acceln => 32 Notes on Data Rates and Process LOFAR Surveys: 230 Gbytes/hour/beam (32 MHz/16-bit/Stokes I) 16 bms = 920 Gbytes/hr (4bit) About 32 Tbytes for 4 hrs FFT 200 khz beamlets ( real time BG/ Offline Beowulf) 1 hr obs = 1 hr proc (128 node) for dedispersion + 30 minutes for basic search (no acceln) In a 4 hr session we have 64 bms so need 4 days processing

16 Notes on Data Rates and Process LOFAR Known Pulsar Observations: Baseband (assumed already dedispersed) 506N TABS MB/s (1%) Dedispersed on BG, 32MHz/164 channels, 200 us 4.9N TABS MB/s max TABs likely 50 Maybe can do more processing on BG to reduce rate to store 24 hours of observation needs about 45 Tbytes temp storage Much of processing can be done on the streaming data (BG) If this is not possible then something like a

17 A testing ground for the SKA A lot of issues facing LOFAR for pulsar work are similar to SKA Incoherent subarray/station vs Many pencil beam surveys Incoherent => lower data rate, long obs, acceleration searches Coherent => much more data, less searching acceleration Large data flows, processing on streaming data? Real time searching? Number of DMs and channels likely to be similar or less

18 Conclusions LOFAR will find at least???? normal pulsars If there is a popn. of steep spectrum pulsars it Long pointings mean it will also find transient A complete census of the local NS populatio The ASM will also reveal many more transi The raw sensitivity of LOFAR will enable related to how RNSs emit (single pulses, It will also provide an excellent probe o both the local electron density and magne It will also reveal things we haven t even There are many computational chall