PULSAR SURVEYS (AO & GBT) Why? How deep can we go? (D max, V max ) Example surveys Hardware Funding

Why more pulsars? Extreme Pulsars: P 5 sec P orb 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? D max = D (S / S min1 ) 1/2 N h 1/4 S min1 = single harmonic threshold = m S sys /(  T) 1/2 m = no. of sigma N h = no. of harmonics that maximize harmonic sum N h  0 for heavily broadened pulses Regimes: Luminosity limited D max  S min1 -1/2 DM/SM limited D max  S min1 -x, x<1/2

Finding D max beam luminosity beam widths (core,cone) orientation angles (  pulse shape at nominal distance (1 kpc) D max = D nom [H(N h )/S min1 ] 1/2 H(N h ) = max N h -1/2  W i W ORB W DM W SM W TC W HPF [ D max = D max (DM, SM)  iterate ]

SEARCH VOLUME: V S =   S D 3 max DETECTION VOLUME: V d =  S  0 Dmax dD D 2 n p /n p (sun)

Regimes for D max Luminosity limited: (r -2 law) Dispersion limited:  t   ch DM / 3 Scattering limited:  t  SM 5/6 / 4.4 Time constant limited:  t TC  t TC (min) = (  ch ) -1

Dmax example

Dmax vs L p

Dmax vs. P (0.43 GHz)

Dmax vs. P (larger L p )

Dmax vs. P (1.4 GHz)

Dmax for B (L band)

Implications After maximizing  T (RFI,TAC constraints), the control parameters for Dmax are l,b,,N ch  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) S sys  N ch T S min1 d  /dT (Jy) (MHz) (s) (  Jy) (hr/deg 2 ) AO /N b GBT /N b Parkes (N b=13 )

Compare AO,GBT & Parkes(Lband) DM c Dmax for L p =10 mJy kpc 2,l=30,b=5  ms33 ms 89 ms AO27 3 kpc8 kpc 8 kpc GBT Parkes

Strawman AO Surveys L band 7 beams 400 MHz/512 channels/beam (multi WAPP) 300 s/beam  6 hr/deg hr  500 deg 2 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 S min1 ) e.g.along spiral arm tangents Cygnus region | b | > few degrees (period dependent)

Shopping List Multibeam system (Feeds/Rx) e.g. 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, AO?) $$$: NSF MRI consortium proposal, private funding?