Scuola nazionale de AstrofisicaRadio 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

• 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.

Why find more pulsars?

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.

Survey SensitivityLimiting mean flux density:

Parkes Multibeam Pulsar Survey

Much reduced sensitivity for short-period high-DM pulsars

Early large-scale searchesSecond Molonglo Survey (1978):

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

PSR J0437-4715

Parkes 70cm Survey (1996):

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

Pulsars in Globular Clusters

• 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)

47 Tucanae:

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!

Millisecond pulsars in other clusters NGC 6266 NGC 6397 NGC6544 NGC 6752PSR 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 >0.19 Msun >0.18 Msun >0.009 Msun (10 MJup) >0.19 Msun

d 6.7 kpc 2.2 kpc 2.5 kpc 3.9 kpcD’Amico et al. (2001)

tint = 54 h!

(Hessels et al. 2006)

(Ransom et al. 2005)

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 - 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 > 0.14 M

PSR J1748-2446ad

Interpulse

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)

G292.0+1.8 – PSR J1124-5916

(Hughes et al. 2001)

• Some young pulsars have very low radio luminosity

• Most SNR may contain a pulsar!

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

The Parkes radio telescope has found more than twice as many pulsars as the rest of the world’s telescopes put together.

Parkes Multibeam Pulsar Survey

Principal papers:

• Covers strip along Galactic plane, -100o < l < 50o, |b| < 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

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

Galactic Distribution of Pulsars

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

(Burgay et al. 2006)

The Parkes High-Latitude Multibeam Survey

• 220o < l < 260o, |b| < 60o

• Samp. int. 125 ms, obs. time 4 min• 6456 pointings

• 18 discoveries, 42 pulsars detected

• 4 MSPs, including the double pulsar!J0737-3039A/B

W=1%

W=5%

W=30%

Non-detections

The PALFA Survey - A multibeam survey at Arecibo• 7-beams, 1.4 GHz, 100 MHz (300 MHz later), 256 channels• 32o < l < 77o, 168o < l < 214o, |b| < 5o

• Samp. Int. 64 s, obs time 134 (67) s• Preliminary analysis: 11 discoveries, 29 redetections• Full survey:1000 new psrs

(~375 - Lorimer et al. 2006a)(Cordes et al. 2006)

PSR J1906+0746• 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)

Galactic Distribution of Pulsars

• 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 > 0.1 mJy kpc2 ~ 0.34 0.05/century

• With beaming correction ~ 1.3 /century

Lyne et al. (1985) Ne Model (S)

Cordes & Lazio (2002) Ne Model (C)

(Lorimer et al. 2006a)

Pulsar Death

Period (s)(Vranesevic et al. 2004)

(Chen & Ruderman 1993)

• 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”

• 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

.

Low B

High B

• High-mass MS companion:P medium-long, Pb large, highly eccentric orbit, youngish pulsar4 known, e.g. B1259-63

• Double neutron-star systems:P medium-short, Pb ~ 1 day, highly eccentric orbit, pulsar old8 + 2? known, e.g. B1913+16

• Young pulsar with massive WD companion:P medium-long, Pb ~ 1 day, eccentric orbit, youngish pulsar2 known, e.g. J1141-6545

• Pulsars with planets:MSP, planet orbits from months to years, circular2 known, e.g. B1257+12

• Intermediate-Mass systems:P medium-short, Pb ~days, circular orbit, massive WD companion, old pulsar 12 + 2? known, e.g. B0655+64

• 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

Types of Binary Pulsars (Stairs 2004)

Binary Evolution

(Stairs 2004)

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?

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 secondary’s 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)

End of Part 3

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

(Roberts et al. 2003)

Chandra (Wiesskopf et al. 2000; Pavlov et al 2004)(Ng & Romani 2003)

Crab Vela

Red: LE X-ray

Green: Radio

Blue: HE X-ray