PULSARS & TRANSIENT SOURCESPULSARS & TRANSIENT SOURCES Pushing the Envelope with SKAPushing the Envelope with SKA

Jim Cordes, CornellJim Cordes, Cornell10 July 200110 July 2001

Neutron Star Science & Pulsar Surveys Transient sources SKA = prolific, specific modes needed

Why more pulsars?• Extreme Pulsars:

• P < 1 ms P > 5 sec

• Porb < hours B > 1013 G

• V > 1000 km s-1

• Population & Stellar Evolution Issues (NS-BH binary)

• Physics payoff (core-collapse processes, EOS, QED processes, GR, LIGO, GRBs…)

• Serendipity (strange stars, transient sources)

• New instruments (AO, GBT, SKA) can dramatically increase the volume searched (galactic & extragalactic)

SKA GALACTIC PULSAR CENSUS

> 1.4 GHz: detect all pulsars beamed toward us

100,000 x 0.2 = 20,000 pulsars

Can detect many pulsars in short period binaries

(large G/T short integration times)

Presumably will find exotic objects as counterparts tohigh energy objects (magnetars, SGRs, etc.)

Can detect significant numbers of pulsars in theGalactic center star cluster (10 GHz)

INTERSTELLAR DISPERSIONINTERSTELLAR DISPERSION

DM = 0D ds ne(s)

DM -3

Pulse broadening (recent AO results, R. Bhat et al)Pulse broadening (recent AO results, R. Bhat et al)

~ D2/2c -4

Pulse broadening

Dmax vs. Flux Density Threshold

Luminosity limited

Dispersion limited

Scattering limited

Parkes MB Feeds

Surveys Surveys with Parkes, with Parkes, Arecibo & Arecibo & GBT.GBT.

Simulated & Simulated & actualactual

Yield ~ 2000 Yield ~ 2000 pulsars.pulsars.

www.astro.cornell.edu/~cordes

SKA pulsar SKA pulsar surveysurvey

600 s per 600 s per beambeam

~10~1044 psr’s psr’s

Pulsar YieldPulsar YieldUp to 104 pulsars (~105 in MW, 20% beaming)

NS-NS binaries (~ 100, merger rate)

NS-BH binaries (?)

Planets, magnetars etc.

Pulsars as probes of entire Galaxy:• spiral arms• pulsar locations vs. age• electron density map (all large HII regions sampled)• magnetic field map from Faraday rotation• turbulence map for WIM (warm ionized medium)

TRANSIENT SOURCES TRANSIENT SOURCES

Sky Surveys:Sky Surveys:

The X-and-The X-and--ray sky has been monitored highly -ray sky has been monitored highly successfully with wide FOV detectors successfully with wide FOV detectors (e.g. RXTE/ASM, CGRO/BATSE).

The transient radio sky (e.g. t < 1 month) is largely The transient radio sky (e.g. t < 1 month) is largely unexplored.unexplored.

New objects/phenomena are likely to be discovered New objects/phenomena are likely to be discovered as well as the predictable classes of objects.as well as the predictable classes of objects.

TRANSIENT SOURCES (2)TRANSIENT SOURCES (2)TARGET OBJECTS:TARGET OBJECTS:

• Neutron star magnetospheres

• Accretion disk transients (NS, blackholes)

• Supernovae

• Gamma-ray burst sources

• Brown dwarf flares (astro-ph/0102301)

• Planetary magnetospheres & atmospheres

• Maser spikes

• ETI

TRANSIENT SOURCES (3)TRANSIENT SOURCES (3)TARGET PROCESSES:TARGET PROCESSES:

• Intrinsic:incoherent ( brightness limit) coherent (virtually no limit)

continuum: low frequencies favored line: masers

• Extrinsic:scintillationmaser-maser amplificationgravitational lensingabsorption events

TRANSIENT SOURCES (4)TRANSIENT SOURCES (4)Certain detectionsCertain detections::

• Analogs to giant pulses from the Crab pulsar out to ~5 Mpc

• Flares from brown dwarfs out to at least 100 pc.

• GRB afterglows to 1 µJy in 10 hours at 10 .

PossibilitiesPossibilities::

• -ray quiet bursts and afterglows?-ray quiet bursts and afterglows?

• Intermittent ETI signals?Intermittent ETI signals?

• Planetary flares?Planetary flares?

Crab Pulsar

OBSERVABLE DISTANCES OF CRAB PULSAR’S OBSERVABLE DISTANCES OF CRAB PULSAR’S GIANT PULSESGIANT PULSES

MSP B1937+21

J1907+0918

226 ms

DM = 358

J1909+0909

223 ms

DM = 421

Giant Pulses from Nearby GalaxiesGiant Pulses from Nearby Galaxies

SCIENTIFIC RETURNSCIENTIFIC RETURN

• Many objects Many objects map out IGM as well as ISMs of map out IGM as well as ISMs of

galaxiesgalaxies

• IGM: electron density and magnetic fieldIGM: electron density and magnetic field

• NS birth rates in other galaxiesNS birth rates in other galaxies

• Constraints on IMFConstraints on IMF

• Census of young pulsars, clues about magnetars?Census of young pulsars, clues about magnetars?

M33

Beam 2

Methods with the SKAMethods with the SKA

I. Target individual SNRs in galaxies to5-10 Mpc

II. Blind Surveys: trade FOV against gain by multiplexing SKA into

subarrays.

III. Exploit coincidence tests to ferret out RFI, use multiple beams.

Summary • Prolific pulsar/transient science for the SKA

• Pulsar surveys: need high G/T and solid angle coverage (with some trade off)

• Transients: Want as large FOV as possible (e.g. hemispheric). Full G/T of SKA not necessarily needed. Exploit coincidence tests from spatially separated stations

• Timing: need many narrow beams

• Astrometry: SKA with long baselines (parallaxes across the Galaxy)

Full Radio Census of Spin-Driven Pulsars

• 1200 known radio pulsars

• 105 active in Galaxy (20% beamed to us)

• detect 10 to 20,000

mapping of ionized gas (“DM tomography”)

identification of rare binaries

10-20 yr project (Arecibo, GBT, FAST,SKA)

How Far Can We Look?Dmax = D (S / Smin1 )1/2 Nh

1/4

Smin1 = single harmonic threshold = m Ssys /( T)1/2

m = no. of sigma ~ 10 Nh = no. of harmonics that maximize harmonic sum

Nh 0 for heavily broadened pulses

Regimes:

Luminosity limited Dmax Smin1 -1/2

DM/SM limited Dmax Smin1 -x , x<1/2

I. Arecibo Galactic-Plane Survey

• |b| < 5 deg, 32 deg < l < 80 deg

• 1.35 GHz total bandwidth = 300 MHz

• digital correlator backend (1024 channels)(1st quadrant available = WAPP)

• multibeam system (7 feeds)

• 300 s integrations, 3000 hours total

• Can see 2.5 to 5 times further than Parkes(period dependent)

• Expect at least 1000 new pulsars

APPROACH

WHAT CAN SKAs DO:

• In physics space (processes, conditions)?

• In observation space?

POSSIBLE ANSWERS:

• Based on known objects.• Extrapolate from rate of previous discoveries

to new parameter space.

NEUTRON STARS PHYSICS SPACE

• Census of stellar evolution pathways

- spin-driven pulsars, magnetars, strange stars…)

- companion objects (WD, NS, BH, planets …)

• Tests of strong gravity (pulse timing)

• Extreme magnetic fields (>> 1012 Gauss)

• Processes in core-collapse supernovae (~ 1 sec)

- mass, photon, neutrino rockets

GUITAR NEBULA PULSAR

NEUTRON STARS PHYSICS SPACE (continued):

Intervening Media:

• Interstellar Medium (ISM)

- phase structure, turbulence

- sculpting by supernovae

- galactic structure:

(spiral arms, molecular ring, bar)

• Intergalactic Medium (IGM)

NEUTRON STARS PHYSICS SPACE (continued):

Full Galactic Census:

• NS birthrate in Galaxy (BR)

• Relation to supernova rate

• BR(t), BR(X) (starbursts in Galaxy)

• Comparison with BR in nearby galaxies

• Intergalactic Medium (IGM)

NEUTRON STARS PHYSICS SPACE (continued)

ENDGAMES:

• Coalescence (NS-NS, NS-BH, NS-WD binaries)

• Escape from the Galaxy

• Relationship to GRBs

GUITAR NEBULA PULSAR

NEUTRON STARS OBSERVATION SPACE

• large G/T search volume (G/T)3/2

(modulo propagation effects)

• high-resolution sampling in f-t plane

(searching, scintillations)

• teraflops post processing

• multiple simultaneous beams for

(a) searching

(b) timing of pulsars

INTERSTELLAR DISPERSIONINTERSTELLAR DISPERSION

INTERSTELLAR SCATTERINGINTERSTELLAR SCATTERING

NEUTRON STARS OBSERVATION SPACE (continued)

• High angular resolution for astrometry

• VLBI resolution needed

• SKA == VLB array

• SKA == station in VLB array

• Currently ionosphere limited (

• SKA at high frequencies: parallaxes to greater D

(can go to > 5 kpc)

PERIODICITY SEARCHES

ADVANTAGES OF SKA:

• large G/T

• large FOV

Galactic Pulsars:

Dmax (G/T)1/2 Nh1/4 - /2

Vmax Dmax3 local

Dmax2 disk

Go to high frequencies:

less flux but less scattering

net increase in search volume

SKA GALACTIC PULSAR CENSUS

> 1.4 GHz: detect all pulsars beamed toward us

100,000 x 0.2 = 20,000 pulsars

Can detect many pulsars in short period binaries

(large G/T short integration times)Presumably will find exotic objects as counterparts tohigh energy objects (magnetars, SGRs, etc.)

Can detect significant numbers of pulsars in theGalactic center star cluster (10 GHz)

TRANSIENT SOURCES PHYSICS SPACE

OBJECTS:

• Neutron star magnetospheres

• Accretion disk transients (NS, blackholes)

• Gamma-ray burst sources

• Planetary magnetospheres & atmospheres

• Maser spikes

• ETI

TRANSIENT SOURCES PHYSICS SPACE

PROCESSES:

• Scintillation induced vs. intrinsic

• Doppler boosting vs. inverse-Compton violations

• Coherent vs. incoherent sources

PERHAPS THE MOST PROMISING:

• FISHING EXPEDITION: NEW FISH

TRANSIENT SOURCESOBSERVATION SPACE

• G/T (of course)

• Large instantaneous FOV

• dedispersion of time series (real time, multiple trial DMs)• event testing for wide range of signal complexity• best case: hemispheric coverage

GUITAR NEBULA PULSAR

CRAB GIANT PULSES

> 105 Jy peak, < 50 micro sec wide @ 1/hr, 400 MHz

• A young pulsar phenomenon?

• Millisecond pulsars too?

Dmax 1.5 Mpc (Arecibo)

5 Mpc (SKA)

OBSERVABLE DISTANCES OF CRAB PULSAR

Giant Pulses from Nearby Galaxies

• Wide field sampling of f-t plane

• Target individual supernova remnants (on/off)

• Expect > 10 Crabs / galaxy

• 10s - 100s of galaxies < 5 Mpc

• Dedisperse with trial DMs

• Threshold test (after matched filter)

• Reality checks: multiple hits @ same DM

more hits on source

Giant Pulses from Nearby Galaxies

SCIENTIFIC RETURN

• Many objects map out IGM as well as ISMs of

galaxies

• IGM: electron density and magnetic field

• NS birth rates in other galaxies

• Constraints on IMF

• Census of young pulsars, clues about magnetars?

Narrow pulses: Tb limits

• W = pulse width

• Spk = peak flux density

= 0.29 microJy T12 -2 W2 / Dkpc2

SUMMARY• SKA can dramatically alter our knowledge of galactic compact objects. Currently population models are highly leveraged from small samples.• A full census of galactic pulsars will allow thorough mapping of NS birth sites, electron density, and B.• SKA will discover significant numbers of extragalactic pulsars, allowing studies of the IGM, stellar evolution, occurrence of high-B magnetospheres, runaway pulsars, constraints on core-collapse processes.• The preferred SKA configuration will fit into the current specifications for some but not all science goals (esp. transient surveys).• Search algorithms require proportionate funding of real-time and offline processing capability.

Milky Way CensusMilky Way CensusTargets:Targets: Molecular cloud regions

YSOs, jets

Main sequence stars (thermal!)

Evolving & evolved stars

Full Galactic CensusFull Galactic Census:

microquasars

radio pulsars (P-DM searches, SKA-VLBI astrometry)

SNR-NS connections (SGRs, magnetars, etc.)