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PULSAR SURVEYS (AO & GBT)

PULSAR SURVEYS (AO & GBT). Why? How deep can we go? (D max , V max ) Example surveys Hardware Funding. Why more pulsars?. Extreme Pulsars: P < 1 ms P > 5 sec P orb < hours B > 10 13 G V > 1000 km s -1. Population & Stellar Evolution Issues

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PULSAR SURVEYS (AO & GBT)

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  1. PULSAR SURVEYS(AO & GBT) Why? How deep can we go? (Dmax, Vmax) Example surveys Hardware Funding

  2. Why more pulsars? • Extreme Pulsars: • P < 1 ms P > 5 sec • Porb < hours B > 1013 G • V > 1000 km s-1 • Population & Stellar Evolution Issues • Physics payoff (GR, LIGO, GRBs…) • Serendipity (strange stars, transient sources) • New instruments (AO, GBT, SKA) can dramatically increase the volume searched (galactic & extragalactic)

  3. Simulated DM vs l histogram (50k pulsars)

  4. How Low Can We Go? Dmax = D (S / Smin1 )1/2 Nh1/4 Smin1 = single harmonic threshold = m Ssys /(Dn T)1/2 m = no. of sigma Nh = no. of harmonics that maximize harmonic sum Nh  0 for heavily broadened pulses Regimes: Luminosity limited Dmax  Smin1 -1/2 DM/SM limited Dmax  Smin1 -x , x<1/2

  5. Finding Dmax • beam luminosity • beam widths (core,cone) • orientation angles (a,b) • pulse shape at nominal distance (1 kpc) • Dmax = Dnom [H(Nh)/Smin1]1/2 • H(Nh) = • max Nh-1/2  Wi WORB WDM WSM WTC WHPF • [ Dmax =Dmax (DM, SM)  iterate ]

  6. SEARCH VOLUME: VS =  S D3max DETECTION VOLUME: Vd = S 0Dmax dD D2np/np(sun)

  7. Regimes for Dmax Luminosity limited: (r -2 law) Dispersion limited: t  ch DM / 3 Scattering limited: t  SM5/6 / 4.4 Time constant limited: tTC tTC(min) = (ch)-1

  8. Dmax example

  9. Dmax vs Lp

  10. Dmax vs. P (0.43 GHz)

  11. Dmax vs. P (larger Lp)

  12. Dmax vs. P (1.4 GHz)

  13. Dmax for B1933+16 (L band)

  14. Implications • After maximizing T (RFI,TAC constraints), the control parameters for Dmax are l,b,,Nch •  optimal directions to search (modulo RF and where pulsars are) • Coherent dedispersion for searches? (not worth it if scattering limited… better to put processing power into binary searches)

  15. AO, GBT, Parkes

  16. Compare AO,GBT & Parkes(Lband) Ssys Dn Nch T Smin1 d/dT (Jy) (MHz) (s) (Jy) (hr/deg2) AO 3.6 400 1024 300 73 42/Nb GBT 16 400 1024 900 190 4.5/Nb Parkes 36 288 96 2100 360 1 (Nb=13)

  17. Compare AO,GBT & Parkes(Lband) DMc Dmax for Lp=10 mJy kpc2 ,l=30,b=5 0.5 ms 33 ms 89 ms AO 27 3 kpc 8 kpc 8 kpc GBT 54 2.8 5 5 Parkes 28 1.3 4 4

  18. Strawman AO Surveys L band 7 beams 400 MHz/512 channels/beam (multi WAPP) 300 s/beam  6 hr/deg2 3000 hr  500 deg2 Search volume  3 to 20 x Parkes MB (l,b,P dependent) S band? Advantage for very fast,weak pulsars & flat spectrum pulsars at low b

  19. AO at S,L,P bands

  20. OPTIMAL DIRECTIONS • AO advantage: collecting area smaller channel bandwidths •  choose directions where Parkes MB is luminosity or DM limited. (SM limited  less advantage per decrease in Smin1) • e.g. along spiral arm tangents Cygnus region | b | > few degrees (period dependent)

  21. Shopping List • Multibeam system (Feeds/Rx) e.g. 7 @ L • Digital backends (multi WAPP) • Data storage • Processing • Followup • $$$ for all of the above

  22. Ideas • Multibeam systems: e.g. Rick Fisher’s focal plane sampling + beamforming system • Digital backends: AO: WAPP x 4 x Nbeams GBT: GBT correlator + fast dump • Storage/processing: Moore’s law • Followup: dedicated timing telescopes (85ft, 1HT, 100ft @ AO?) • $$$: NSF MRI consortium proposal, private funding?

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