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)

Simulated DM vs l histogram (50k pulsars)

How Low Can We Go?Dmax = D (S / Smin1 )1/2 Nh

1/4

Smin1 = single harmonic threshold = m Ssys /( 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 (• 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

Dmax example

Dmax vs Lp

Dmax vs. P (0.43 GHz)

Dmax vs. P (larger Lp)

Dmax vs. P (1.4 GHz)

Dmax for B1933+16 (L band)

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)

AO, GBT, Parkes

Compare AO,GBT & Parkes(Lband)

Ssys 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

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 band7 beams400 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

AO at S,L,P bands

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 NbeamsGBT: GBT correlator + fast dump

• Storage/processing: Moore’s law

• Followup: dedicated timing telescopes (85ft, 1HT, 100ft @ AO?)

• $$$: NSF MRI consortium proposal, private funding?