Scuola nazionale de Astrofisica

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Scuola nazionale de Astrofisica Radio Pulsars 3
Searches and Population Studies
Outline

• Methods and early searches
• Globular Cluster searches
• Parkes Multibeam searches
• Galactic distribution of pulsars
• Birth rate and evolution

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Why find more pulsars?

• Pulsars are excellent clocks, leading to many
  interesting experiments in physics and
  astrophysics.
• Pulsars are excellent probes of the interstellar
  medium and are widely distributed in the Galaxy.
• A few especially interesting objects with unique
  properties will probably be found in a
  large-scale survey.
• Leads to a better understanding of the Galactic
  distribution and birthrate of pulsars, of binary
  and stellar evolution, of their relationship to
  other objects such as supernova remnants, and of
  the emission physics.

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Search Methods

• First searches used chart recorders and detected
  individual pulses
• In early 1970s, digital recording and Fourier
  search techniques introduced
• Because of interstellar dispersion, have to
  split signal into many narrow frequency bands
  using an analogue filterbank or digital
  spectrometer
• Four basic analysis steps
• dedispersion
• Fourier analysis to give modulation spectrum
• harmonic summing
• form mean pulse profile at candidate period
• These steps performed for many different trial
  dispersions
• Candidates with S/N above some threshold
  (typically 8?) saved
• Most candidates (especially near threshold) are
  spurious - often due to radio-frequency
  interference
• Candidates confirmed (or not) by re-observing
  same position and looking for same period/DM
• Timing observations for 1-2 years on confirmed
  pulsars to determine accurate position, period,
  period derivative, binary parameters etc.

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Survey Sensitivity
Limiting mean flux density
Parkes Multibeam Pulsar Survey
Much reduced sensitivity for short-period high-DM
pulsars
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Early large-scale searches
Second Molonglo Survey (1978)

• All sky ? lt 25o.
• Detections at Molonglo, confirmations at Parkes
• Discovered 155 pulsars - doubled number known at
  the time

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Parkes 70cm Survey (1996)

• Southern hemisphere, ? lt 0
• First major (southern) survey sensitive to MSPs
• 101 pulsars discovered, including 17 MSPs, 12
  binaries

PSR J0437-4715
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Pulsars in Globular Clusters
47 Tucanae

• 11 millisecond pulsars discovered 1991-1995. All
  but two single (non-binary)
• 12 more discovered since 1998 using multibeam
  receiver. All but two binary.

(Camilo et al. 2000)
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Ionized gas in 47 Tucanae
.

• Correlation of DM and P
• P due to acceleration in cluster potential
• Pulsars on far side of cluster have higher DM
• Gas density 0.07 cm-3, about 100 times local
  density
• Total mass of gas in cluster 0.1 Msun

.
(Freire et al. 2001)
First detection of intra-cluster gas in a
globular cluster!
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Millisecond pulsars in other clusters
NGC 6266 NGC 6397
NGC6544 NGC 6752 PSR J1701-30
PSR J1740-53 PSR J1807-24 PSR J1910-59
P 5.24 ms 3.65 ms
3.06 ms 3.27 ms Pb 3.81 d
1.35 d (eclipse) 0.071 d (1.7 h) 0.86 d
Mc gt0.19 Msun gt0.18 Msun gt0.009
Msun (10 MJup) gt0.19 Msun d 6.7 kpc
2.2 kpc 2.5 kpc
3.9 kpc
DAmico et al. (2001)
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GBT Search of Globular Cluster Terzan 5

• 600 MHz bandwidth at 2 GHz
• 5.9h obs with 82 ?s sampling
• Smin 15 ?Jy
• 31 pulsars discovered!! 33 total in cluster
  (www.naic.edu/pfreire/GCpsr.html)
• Two eccentric relativistic binaries N-star
  1.7 M??

PSR J1748-2446ad
(Ransom et al. 2005)

• PSR J1748-2446ad - fastest known pulsar!
• P 1.3959 ms, f0 716.3 Hz, S2000 80 ?Jy
• Binary, circular orbit, Pb 1.09 d
• Eclipsed for 40 of orbit
• mc gt 0.14 M?

tint 54 h!
Interpulse
(Hessels et al. 2006)
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Pulsar - SNR Associations

• Big increase in last few years
• Mostly due to detection of X-ray point sources
  in SNR by Chandra
• In some, pulses detected directly in Chandra
  data
• In others, deep radio search reveals pulsar
• e.g., PSR J1124-5916, detected in 10.2-hr
  observation at Parkes (Camilo et al. 2002)

G292.01.8 PSR J1124-5916

• Some young pulsars have very low radio
  luminosity
• Most SNR may contain a pulsar!

(Hughes et al. 2001)
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Parkes Multibeam Pulsar Surveys

• More than 880 pulsars discovered with multibeam
  system.
• The Parkes Multibeam Pulsar Survey (an
  international collaboration with UK, Italy, USA,
  Canada and Australia) has found 760 of these
  (including RRATs).
• High-latitude surveys have found 120 pulsars
  including 15 MSPs
• 14 pulsars found in Magellanic Clouds

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The Parkes radio telescope has found more than
twice as many pulsars as the rest of the worlds
telescopes put together.
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Parkes Multibeam Pulsar Survey

• Covers strip along Galactic plane, -100o lt l lt
  50o, b lt 5o
• Central frequency 1374 MHz, bandwidth 288 MHz,
  96 channels/poln/beam
• Sampling interval 250 ?s, time/pointing 35 min,
  3080 pointings
• Survey observations commenced 1997, completed
  2003
• Processed on work-station clusters at ATNF, JBO
  and McGill
• 1015 pulsars detected
• At least 18 months of timing data obtained for
  each pulsar

Principal papers
I Manchester et al., MNRAS, 328, 17
(2001) System and survey description, 100
pulsars II Morris et al., MNRAS, 335, 275
(2002) 120 pulsars, preliminary population
statistics III Kramer et al., MNRAS, 342, 1299
(2003) 200 pulsars, young pulsars and ?-ray
sources IV Hobbs et al., MNRAS, 352, 1439
(2004) 180 pulsars, 281 previously known
pulsars V Faulkner et al., MNRAS, 355, 147
(2004) Reprocessing methods, 17 binary/MSPs VI
Lorimer et al., MNRAS, 372, 377 (2006) 142
pulsars, Galactic population and evolution
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Galactic Distribution of Pulsars
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Parkes Multibeam Surveys P vs P
.
J1119-6127

• New sample of young, high-B, long-period pulsars
• Large increase in sample of mildly recycled
  binary pulsars
• Three new double-neutron-star systems and one
  double pulsar!

J0737-3039
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The Parkes High-Latitude Multibeam Survey

• 220o lt l lt 260o, b lt 60o
• Samp. int. 125 ms, obs. time 4 min
• 6456 pointings

W30
W5
W1
Non-detections

• 18 discoveries, 42 pulsars detected
• 4 MSPs, including the double pulsar!

J0737-3039A/B
(Burgay et al. 2006)
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The PALFA Survey - A multibeam survey at Arecibo

• 7-beams, 1.4 GHz, 100 MHz (300 MHz later), 256
  channels
• 32o lt l lt 77o, 168o lt l lt 214o, b lt 5o
• Samp. Int. 64 ?s, obs time 134 (67) s
• Preliminary analysis 11 discoveries, 29
  redetections
• Full survey1000 new psrs (375 -
  Lorimer et al. 2006a)

(Cordes et al. 2006)
PSR J19060746

• 144-ms pulsar in 3.98-h binary orbit
• Highly relativistic, ? 7.6o/yr
• mp mc 2.61 ? 0.02 M?
• Pulsar is young! ?c 112 kyr
• Companion either a massive white dwarf or a
  neutron star (observed pulsar is the second born)
• Coalescence time 300 Myr

(Lorimer et al. 2006b)
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Galactic Distribution of Pulsars
Lyne et al. (1985) Ne Model (S)

• Only see a small fraction of pulsars in Galaxy
  because of selection effects
• Sensitivity limit is the main effect - distant
  low-luminosity pulsars not detected
• Number of potentially detectable pulsars in
  Galaxy 30,000 ? 1100
• With beaming correction 150,000
• Derived radial distribution very dependent on
  Galactic ne model
• z scale height 330 pc (Model S), 180 pc (Model
  C) - larger scale height more consistent with
  other results
• Birthrate of potentially observable pulsars L gt
  0.1 mJy kpc2 0.34 ? 0.05/century
• With beaming correction 1.3 /century

Cordes Lazio (2002) Ne Model (C)
(Lorimer et al. 2006a)
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Pulsar Death
.

• For constant Bs, pulsars evolve along lines with
  PP constant
• Pulsar death due to cessation of pair production
  - death line
• Location of death line dependent on assumptions
  about acceleration region and mechanism - death
  valley

Low B
(Chen Ruderman 1993)

• In observed P histogram N(logP) P2 if no death
• Peak in P histogram at 0.6 s therefore most
  pulsars die well before death line reached
• Luminosity decay means longer-period pulsars
  harder to detect - selection effect
• Pulsar current analysis corrects for selection
  effects
• Suggests that many high-B born with intermediate
  P

High B
Period (s)
(Vranesevic et al. 2004)
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Types of Binary Pulsars
(Stairs 2004)

• High-mass MS companion
• P medium-long, Pb large, highly eccentric orbit,
  youngish pulsar
• 4 known, e.g. B1259-63
• Double neutron-star systems
• P medium-short, Pb 1 day, highly eccentric
  orbit, pulsar old
• 8 2? known, e.g. B191316
• Young pulsar with massive WD companion
• P medium-long, Pb 1 day, eccentric orbit,
  youngish pulsar
• 2 known, e.g. J1141-6545
• Pulsars with planets
• MSP, planet orbits from months to years, circular
• 2 known, e.g. B125712
• Intermediate-Mass systems
• P medium-short, Pb days, circular orbit, massive
  WD companion, old pulsar 12 2? known, e.g.
  B065564
• Low-mass systems
• MSP, Pb hours to years, circular orbit, low-mass
  WD, very old pulsar
• 105 known, 55 in globular clusters, e.g.
  J0437-4715, 47Tuc J

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Binary Evolution
(Stairs 2004)
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Companion Mass - Pulsar Period

• High-mass systems have little or no recycling
  long pulsar period
• Low-mass systems evolve slowly and are spun up
  to shorter periods
• GC systems dominate low-P, low-mass end
• Different evolution?
• Selection effect?
• Limiting pulsar period?
• Ablation with no accretion?

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Eccentricity Binary Period

• Relation predicted for long-period systems by
  Phinney (1992).
• GC systems have higher eccentricity
  interactions with cluster stars
• Unrecycled systems and systems where the primary
  was already a WD or NS at the time of the
  secondarys collapse have very high eccentricity
• But many DNS systems have only moderate
  eccentricity
• Small kick?
• More rapid evolution for high-eccentricity
  systems (Chaurasia Bailes 2005)

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End of Part 3
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X-ray Pulsar Wind Nebulae
.

• Few percent of E radiated as X-rays - PWN
• Very anisotropic - jets and torii
• Can determine 3-D orientation of pulsar spin
  axis!
• Inclination important for pulsar beaming
• Close correlation of spin-axis orientation with
  direction of pulsar velocity
• Neutrino ejection mainly along spin axis?
• Slow kick? (Spruit Phinney 1998)

G11.2-0.3 -- PSR J1811-1925
Red LE X-ray Green Radio Blue HE X-ray
(Roberts et al. 2003)
Crab
Vela
(Ng Romani 2003)
Chandra (Wiesskopf et al. 2000 Pavlov et al 2004)