Pulsars and Transients: ALFA and Beyond
Jim Cordes
Cornell University
• Arecibo and ALFA surveys
• Galactic plane pulsar and
transient survey
• PALFA Consortium
• Prospects
• Context within the era of SKA
pathfinders
• Campaigning for Arecibo
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Focal Plane
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ALFA Science Goals: Massive Surveys
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Extragalactic atomic hydrogen (H I) surveys:
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Interstellar turbulence
Disk-halo connection (chimneys & fountains)
Galactic structure and dynamics
Continuum surveys
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Galactic synchrotron radiation (magnetoionic medium)
Pulsar science:
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(G-ALFA)
Low-and-high-latitude H I surveys
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Zone of avoidance galaxies
All (Arecibo) sky search for low-mass H I clouds and galaxies
High-velocity clouds
Galactic science:
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(E-ALFA)
(P-ALFA)
Deep surveys + follow up pulse timing studies
SETI: to be done simultaneously with pulsar surveys
http://alfa.naic.edu/ (specifications, memos, consortia)
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PALFA Survey Goals
Arecibo can provide the most sensitive high-frequency
surveys until the SKA (but c.f. sky coverage)
500 - 103 pulsars
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Galactic plane survey: |b|<5, 32 < l < 77, ~300s dwell times
Intermediate latitude survey: 5 < |b| < 15 for MSPs, NS-NS
64 s, 256 channels across 100 MHz with current spectrometers
Reach edge of Galactic population for much of luminosity function
High sensitivity to millisecond pulsars (smearing 120 s for DM = 100)
Dmax = 2 to 3 times greater than for Parkes MB
Sensitivity to transient sources (algorithms)
Data management
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Keep all raw data
~ 1 Petabyte after 5 years at the Cornell Theory Center
Database of raw data, data products, end products
Virtual observatory linkage eventually
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PALFA Survey Goals
Pulsars and Gravity:
– Relativistic binaries (NS-WD, NS-NS, NS-BH): as laboratories for
testing GR in the strong-gravity limit
» J1906+0746 (second born NS in NS-NS system)
144 ms, 3.98 hr orbit
» Paper in preparation (Kasian et al.)
– Pulsar timing array objects: millisecond pulsars with low “timing
noise” that allow detection or strong limits on nHz gravitationalwave backgrounds
» J1903+03, 2.15 ms (Champion et al.)
High-energy/radio-pulsar synergies:
» J1928+1746 (68 ms pulsar in EGRET error box)
Intermittent pulsars (RRAT like)
» J0628+09 + 7 others
Galaxy/Interstellar Medium:
– Large number of pulsars allows modeling of electron density and magnetic
field (DM, SM, RM + multi- obs)
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First Results
11 new pulsars: 1 binary, 1 w/ possible
gamma-ray counterpart, 1 transient source
Exploited database of Parkes Multibeam
survey + multiobservatory followup
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The FIRST PALFA Millisecond Pulsar: J1903+03 (Champion et al. in preparation)
P = 2.15 ms
DM = 297 pc cm-3
(highest for any MSP)
S/N = 24.2
Binary
parameters:
Porb = 95 days
e = 0.44
Found in McGill
search pipeline
Confirmed in
Cornell pipeline
with same S/N
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J1903+03 = distant MSP
• Total mass = 2.5 Msun
• Minimum companion mass = 1.0 Msun
• e = 0.44
• High DM pulsar in the Galactic plane:
• narrow channels in survey spectrometers
• number of implied MSPs depends on origin (from GC
or from disk?)
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PALFA Survey Pipeline
Main steps:
• Recording and quicklook analysis
• Shipping data from AO
to CTC
• Full resolution
processing at Cornell
and other sites
• Consolidation of
processing results
into db
• Filtering candidates
for reobservation
http://arecibo.tc.cornell.edu/PALFA
PALFA Databases at Cornell Center for Advanced Computing
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PALFA Status
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Galactic plane survey requires 48k pointings
To date: 14k pointings
120 known pulsars “rediscovered”
36 confirmed discoveries
~ 100 candidates to reobserve 2007 Fall
• Arecibo downtime summer 2007 for painting
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Signal Signatures
• Classic: sharp pulses, steady amplitudes
• Realism: expect low duty cycle pulsars
• Nearly aligned rotators
• Highly scattered pulsars (large DM, distant)
• Orbitally broadened (mitigated by acceleration search)
• Neo:
• highly intermittent objects (e.g. “RRATs”)
• other source classes:
– Pulsars: TOE simultaneous, TOA differential (dispersion)
– Other transients: TOE  simultaneous, TOA differential
• Realism II: RFI
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DM
Frequency
Pulsar Periodicity Search
time
time
FFT each DM’s
time series
|FFT(f)|
1/P
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2/P 3/P
  
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Single pulse searches
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Two pulsars in one beam
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Signal detection through
stacked multiple single
pulses (dedispersed)
Stacked signal in
the frequency-time
plane (dispersion
signature)
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Single-pulse vs. Periodicity Detection
Have pulsars been missed?
r = (S/N)SP / (S/N)FFT
Higher S/N from
SP detection
r>1 implies SP detection
more efficacious
Depends on number of
periods Np in the data set
Higher S/N from
FFT analysis
SP detection tends to be
superior for small Np
Implication for future
telescopes (e.g. SKA)
Julia Deneva, work in progress
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Near and Longer Term
• Observations will re-commence ~ 1 Oct ’07
• New spectrometers available this Fall
• 300 MHz total bandwidth vs. 100 MHz of WAPPs
• polyphase filter banks vs. correlators
» May be less affected by RFI
• Timing follow up at Arecibo, GBT (Nice, Stairs,
Lorimer et al.)
• Can expect GP survey and mid-latitude surveys to
continue for many years
• Transient surveys can run simultaneously with the
all-SKY ALFALFA (HI) survey, along with SETI,
etc.
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MeerKAT
Timeline
10% SKA
Phase I
ATA
LOFAR
MWA/LFD
MIRA
 ASKAP
Full SKA
LWA
Now
2008
2009
2014
2020
ATA
Size
LOFAR
MeerKAT
MIRA
100-m class
Full SKA
SKA Phase I
Arecibo class
SKA
A community meeting to
promote Arecibo science
over the next 5 -15 years
The NSF is seeking new
business models for its
facilities
Need to reconvince
ourselves and the
community of Arecibo’s
importance
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Extra Slides
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Dmax vs P
Dmax = maximum
detectable
distance for
period P given
luminosity Lp
Detection curves
take into account
interstellar
scattering
(NE2001 model)
instrumental
effects, additive
noise
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A pulsar found
through its singlepulse emission, not its
periodicity (c.f. Crab
giant pulses).
Algorithm: matched
filtering in the DM-t
plane.
ALFA’s 7 beams
provide powerful
discrimination
between celestial and
RFI transients
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Matched filtering in the t-RF plane
Allow more signal
classes than is typical
c.f. cluster analysis in
LIGO t-f plane for
unmodeled bursts
Post-detection dedispersion:
sum intensity along dispersion path
Coherent dedispersion: unwrap phases
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Figure of Merit for Radio
Survey Capabilities
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For 1.4 GHz
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Blind Surveys with SKA
• Number of pixels needed to cover FOV:
• Npix~(bmax/D)2 ~104
• Number of operations to form beams
• Nops~ petaop/s
≥104 beams needed
for full-FOV sampling
• Post processing per beam:
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Single-pulse and periodicity analysis
Dedisperse (~1024 trial DM values)
FFT + harmonic sum
Orbital searches (acceleration ++)
RFI excision
• Correlation is more efficient than direct beam
formation
• Requires signal transport of individual
antennas to correlator
• Post processing ~ 10% of beam forming
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SKA Program Plan
A personal take on what should be proposed to the Decadal Survey
• EoR Array: < 0.3 GHz
– Science goal: detection and imaging of EoR
– Array optimized for this goal, separable from (the rest of) the SKA
– Context: Informed by LOFAR, MWA, PAPER (detection!)
– Expand later as imaging array contingent on results from current arrays
– Substantial U.S. contribution next decade
• Radio Synoptic Survey Telescope: 0.3 – 3 GHz (higher desireable)
– Survey oriented: Dark Energy, Gravity/Pulsars, Transients, Magnetism,
Relativistic objects
– Consistent with Reference Design but needs technology decisions and
optimization
– U.S. a significant partner with specific deliverables consistent with funding and
time line (E.g., antenna/feed designs, processing algorithms, backends)
• High-frequency Array: 1–25 GHz
– Science goals: Imaging protoplanetary disks, high-z CO, SETI;
– Follow-on to EVLA, ALMA; complementary to JWST, TPF, etc.
– Consistent with Reference Design
– Siting re-evaluated based on characteristics of RSST array site
– Substantial U.S. contribution
– Deferred construction
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Summary
• Target classes for transients
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Relativistic objects (stellar, AGN)
Planets, brown dwarfs
ETI
other?
• Keys to discovery at radio wavelengths
• Time-frequency (t-)
• Wide-field sampling ()
• Low-mid-high sensitivity (smin)
• Blind surveys of the radio sky
• Expand AeT
• Comprehensive matched filtering (computing)
• Start now (Arecibo, GBT, Parkes ATA,LWA,MWASKA1SKA
• The SKA Program:
• RSST for parallel key science
• Cross correlations with other synoptic surveys (EM, CR, GW)
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SKA Science Before the SKA
• Pulsars:
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Strive for full Galactic census (including GCs and GC)
Pulsar timing array: Roadmap from now to the SKA
Techniques for improving timing precision
Faraday RMs
• Transients
• Monitor the sky as much as possible with flexible
analysis of the time-frequency plane
• Solid angle + t-f analysis more important at this stage
than sensitivity
• Explore cross- synergies
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Asteroids around Pulsars:
Relevance to SKA
Asteroid belts can produce significant
timing noise in MSPs from orbital
recoil, influencing the convergence of
relativity tests, mass determinations,
etc.
Long-P pulsars: accreted asteroids
will produce a random walk in spin
phase from torque pulses
Direct detection of tenuous disks is
difficult with current telescopes but
may be likely with the SKA:
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Initial Ideas About Radio Pulsations
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LGMs 1, 2, 3 and 4
White dwarf oscillations
Orbital motion of white dwarfs
Neutron star spins
• Electromagnetic radiation at the spin
frequency
• Lighthouse model (spinning beam): T.
Gold
• Similar richness of interpretations for
Gamma-ray bursts up to 1990s
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Pulsars and Transients: ALFA and Beyond
Jim Cordes
Cornell University
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ALFA and consortium science
Ongoing pulsar and transient survey
• Survey goals
• Discoveries so far
» PDM
» SP
• RFI
» Examples, summary of variability etc.
• Data Management
» End to end pipeline
» Now
» Future
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Prospects
• Current PALFA survey
» New spectrometer
» Data delivery by network
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Out of plane surveys
PTA linkage
Generalized analyses
SKA context
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Ending Points
• The SKA is an ambitious, revolutionary project for tackling
fundamental questions in physics, astrophysics and
astrobiology
• The SKA is likely to be built in three bands with phased
construction over the next 15 years
• SKA-low
• SKA-mid
• SKA-high
<100 MHz to 300 MHz
0.3 to 3 GHz (or higher)
1 to 25 GHz (or higher)
extend EVLA?
• SKA-mid can operate as a Radio Synoptic Survey
Telescope that does a billion-galaxy survey while also
doing gravity/pulsars, magnetic fields and transient
science
• Building the SKA is a challenge in technology
development, in funding and in international politics
• Initial arrays will begin construction this decade.
• Action: develop science roadmaps that link current
facilities with SKA pathfinders and the SKA itself
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