Äîêóìåíò âçÿò èç êýøà ïîèñêîâîé ìàøèíû. Àäðåñ îðèãèíàëüíîãî äîêóìåíòà : http://www.naic.edu/alfa/ealfa/meeting1/talks/cordes.pdf Äàòà èçìåíåíèÿ: Mon May 8 22:43:32 2006 Äàòà èíäåêñèðîâàíèÿ: Sun Dec 23 01:19:18 2007 Êîäèðîâêà: Ïîèñêîâûå ñëîâà: âîåûîéå ðìáîåôù

ALFA Pulsar Surveys
Jim Cordes, Cornell University Arecibo 16 March 2003

· · · · · ·

Pulsar Consortium meeting 1-2 Nov 2002 Preliminary survey plans Hardware needs Organization of the consortium & working groups Synergies with other science goals (EALFA, GALFA) Data management (how to serve 1 Pbyte of data?, long-term archiving)


Targeted Classes of Pulsars
· · · · · · · · · Young, canonical pulsars (Galactic plane) Recycled pulsars (MSPs) (out of plane) High-velocity pulsars NS-NS and NS-BH binaries Pulsars `beyond the death line' (radio magnetars?) Precessing pulsars Globular cluster MSPs X-and--ray selected pulsars Transient sources (e.g. giant pulses)


Why more pulsars?
· Extreme Pulsars: · P < 1 ms · Porb < hours · V > 1000 km s
-1

P > 5 sec B > 10
14

G

· Population & Stellar Evolution Issues · Using pulsars to probe the ISM (gas & magnetic field) · The high-energy connection (e.g. GLAST) · Physics payoff (GR, LIGO, GRBs...) · Serendipity (strange stars, transient sources)


Search processing High Performance Computing + well-organized data management t: 107 : 103

2002: single processor 200 x real time

>2004: a cluster of Beowulf clusters can keep up with real time at observing duty cycle


Pulse broadening from multipath


D

max

vs. Flux Density Threshold

Scattering limited

Dispersion limited

Luminosity limited

ALFA


Implications:
· Optimal integration time:
stay close to the luminosity-limited regime

· Fast-dump spectrometers:
need sufficient number of channels so that search is not DM limited

· Better to cover more solid angle than
integrating longer on a given direction
(as long as all solid angles contain pulsars)


ALFA Pulsar Surveys
I. II. III. Galactic plane |b| < bmax~ 3 to 5 deg Intermediate latitudes (bmax |b| 15 to 25 deg) Deep surveys toward specific objects
- high-energy selected targets (multibeam for RFI) - extended targets (clusters, HII complexes, spiral-arm tangents)

IV. Extragalactic targets
- giant pulses from M33 (~24 ALFA pointings)

V.

Piggyback pulsar/transients survey on high b HI survey? (multiple passes) VI. Other


Nominal Parameters of Galactic Plane Survey
· · · · · · · · 300 MHz bandwidth 1024 channels 64 µs dump time polarizations summed ~4 bits/sample 7 beams 300 s dwell time 400 TB in 2000 hr 30< l < 80 deg |b| < 5 deg 56 MB/s

3 yr @ 50%


Comparison of AO, GBT & Parkes
(S
Site AO
GHz

min1

held fixed)
t µs 64 64 Tint s 20 300 Smin1
µJy

Ssys
Jy


MHz

N

ch

FWHM dT/d
arcmin hr/deg2

1.4

3.6 16 36

*

300 400 288

1024 1024

330 330

3.6 9 14

2.0/Nb 4.7/Nb 13.6/N

GBT 1.4 PMB 1.4

96 250

2100 330

b

* S = 3.6 Jy for Pix > 0 sys

2.8Jy for Pix=0

~ 2.3 Jy for new LBW


Comparison of AO, GBT & Parkes
S S
min1

(AO) << Smin1 (Parkes) Nch TS
(s)
min1

sys


(MHz)

dt/d
(hr/deg2)

(Jy)

(µJy)

AO GBT Parkes

3.6 16 36

300 1024 400 1024 288 96

300

85

29/Nb=4.2 4.5/N
b

900 190 2100 360

1 (Nb=13)


Surveys with Parkes, Arecibo & GBT. Simulated & actual Yield ~ 1000 pulsars.


Spectrometer Requirements
· · · · · · · 300 MHz bandwidth (full feed) <0.3 MHz channels FPGA Correlator or FPGA-FFT or Polyphase filter approach Fast dump capability Polarization summing mode Needs rapid decision (this month)


II. Intermediate Latitude Survey
Search for: · Millisecond pulsars (z scale height ~ 0.5 kpc) · High-velocity pulsars (50% escape) (scale height = ) · NS-NS binaries (typical z ~ 5 kpc) · NS-BH binaries (typical z ~ few kpc ?)
~ 1500 hours (piggyback, filler time?)


Issues for Optimizing Surveys
· RFI management
· Characterization, test obs & algorithms, multibeam schemes (ALFA + other?)

· Diffractive ISS
· multiple passes favored for low DM · -t weighting for intermediate DM · no action for high DM

· Refractive ISS
· multiple passes for low to intermediate DM

· Nulling multiple passes · "Search" vs. "confirmation"
· Historically two different phases · PMB: candidate density Tconfirm ~Tsearch do two "searches" = two passes on sky


What Next?
· New survey simulations
· Population issues (PMB), NE2001 · Optimize number of detections vs l,b,t,etc

· Design at-the-telescope survey modes
· Beam interlace, hour angles, feed rotation

· · · ·

RFI studies, pilot observations, simulations Search code development (~TEMPO, not AIPS++) Data management plan Plan survey follow-up (timing, multi-)


Pulsar Consortium Working Groups
· · · · · Surveys Data acquisition Post processing Data Management Follow-up observations
(J. Cordes) (I. Stairs) (D. Lorimer) (S. Ransom) (B. Gaensler)



Preliminary Protocols
· Consortium membership:
­ open policy early on, by application later ­ protection of student projects

· Data access:
­ ­ ­ ­ open to all members during proprietary period by application from nonmembers (during proprietary period) uniform, baseline processing for legacy goal encourage innovative new approaches

· Authorship:
­ rotating lead, equitable ­ all consortium members ­ opt out by inactive members (honor system)

· Follow up observations: · Discovery of exotica: full

similar to Authorship consortium involvement


Data Management
· Raw data
Local processing (inc. quicklook) Processing at Consortium member institutions Short and long-term archiving (disk/tape) Central mainland location with high-bw pipe? Database catalog system Implied Linkage Web based data selection to the National Intermediate Data products Virtual ­ candidate lists Observatory as ­ RFI identification appropriate ­ diagnostic plots ­ ­ ­ ­ ­ ­

·

· Final products (catalogs, pulse profiles, timing
models)


Pilot Database Storage
(Cornell Theory Center)
Database information: · Microsoft SQL Server · Hosted at the Cornell Theory Center · Stores both raw data and heavily processed data · For the raw data simple queries will select chunks to serve out for users · The processed data can be searched and analyzed with complex queries · Database will be tuned to perform better for common/expected queries


Boundary Conditions etc.
· ALFA surveys can be viewed as part of a long-term, grander effort ("Full Galactic Census") (LOFAR, SKA, ) · ALFA surveys usher in a new NAIC mode of operation (not business as usual) · RFI mitigation required and provides general purpose tools · Data & data products = long term resources data management policy & resources · The scientific pie is large enough for shared glory but ... · A focused, concerted, committed effort is needed for (a) the best surveys (b) legacy results · Exploit telescope time fully (transients, piggybacking)