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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) Why? How deep can we go? (Dmax, Vmax) Example surveys Hardware Funding
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)
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
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 ]
SEARCH VOLUME: VS = S D3max DETECTION VOLUME: Vd = S 0Dmax dD D2np/np(sun)
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
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)
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)
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
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
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)
Shopping List • Multibeam system (Feeds/Rx) e.g. 7 @ L • Digital backends (multi WAPP) • Data storage • Processing • Followup • $$$ for all of the above
Ideas • Multibeam systems: e.g. Rick Fisher’s focal plane sampling + beamforming system • Digital backends: AO: WAPP x 4 x Nbeams GBT: GBT correlator + fast dump • Storage/processing: Moore’s law • Followup: dedicated timing telescopes (85ft, 1HT, 100ft @ AO?) • $$$: NSF MRI consortium proposal, private funding?