Survey
* Your assessment is very important for improving the workof artificial intelligence, which forms the content of this project
* Your assessment is very important for improving the workof artificial intelligence, which forms the content of this project
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 P > 5 sec • Porb < hours B > 1014 G • V > 1000 km s-1 • 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 Dmax vs. Flux Density Threshold Scattering limited Dispersion limited ALFA Luminosity limited 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 s 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 (Smin1 held fixed) Site GHz Ssys Nch t s Tint s hr/deg2 330 3.6 2.0/Nb 330 9 4.7/Nb 2100 330 14 13.6/Nb MHz 3.6* 300 1024 64 20 GBT 1.4 16 400 1024 64 300 PMB 1.4 36 288 *S 1.4 sys = 3.6 Jy for Pix > 0 96 250 Jy FWHM dT/d arcmin Jy AO Smin1 2.8Jy for Pix=0 ~ 2.3 Jy for new LBW Comparison of AO, GBT & Parkes Smin1 (AO) << Smin1 (Parkes) Ssys (Jy) (MHz) Nch T Smin1 dt/d (s) (Jy) (hr/deg2) 85 AO 3.6 300 1024 300 GBT 16 400 1024 900 190 Parkes 36 288 96 2100 360 29/Nb=4.2 4.5/Nb 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: similar to Authorship • Discovery of exotica: full 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)