Aris Karastergiou

pulsar science

searching / timing

emission mechanismbeam structure

polarizationsingle pulses ISM studies

scintillationFaraday Rotation

dispersion/scatteringIGM studies

binary systemsgravity

ionosphere

weak sources raw sensitivity; phased arrays

all-sky distribution, transient wide fov, multiple beams

very fast modulations high (μs) temporal resolution; pulsar backends; huge data rates

ISM and IGM high resolution in frequency, polarization; dedispersion capabilities

3D beam structures broad and continuous frequency coverage

interesting polarization high polarization purity, accurate calibration

raw sensitivity

• pulsars are mJy sources even at 100 MHz

• long integration not an option for most exciting science - individual bursts and pulses, interstellar scintillation, extragalactic sources etc...

where does 100 MHz

emission come from?

lightclosed

openfieldlines

cylinderfieldlines

rotation axis

magnetic axis

radi

o pu

lses

starneutron

radio beam

single pulses• statistics of drifting subpulses: a

key to the emission mechanism

• multifrequency drifting properties

• modulation properties of core and cone components

• irregular drifting

• correlation with pulsar age

• millisecond pulsarsWeltevrede et al.nulling, giant pulses,

microstructure...

phased aperture arrays• extended low frequency dipole arrays - very long

baselines

• beam-forming at station and instrument level

achieve/monitor coherence of dipole/station addition

track & measure beam shape at different sky positions

monitor and correct for ionospheric effects

multiple beams - clock/frequency stability errors

characterization and techniques to avoid RFI

multi-level quasi on-line calibration

...and instrument level.beamforming at station...

How much of each array can be maintained in phase?

wide field-of-view -- multiple beams• powerful surveys - pulsars brightest at ~100 MHz

Flux density spectra of normal vs millisecond pulsars

For pulsar spectra that can satisfactorily fit a single power law, the range of observed spectral indices is broad: 0 >∼ ξ >∼ −4, with a mean value of −1.8±0.2 (Maron et al. 2000)

AA reliable flux calibration

Malofeev et al.

wide field-of-view -- multiple beamsRRATs: How many are there?

What exactly are they? Is their emission mechanism the same as pulsars? Spectrum?

McLaughlin et al.

highest possible time resolution to catch “spiky”

emission - take care in digital beamforming - flexible baseband recorders

wide field-of-view -- multiple beams

At lower frequencies (~ 400 MHz) where many pulsar surveys were conducted, although the steep spectral index of the source implies an even higher flux density, the predicted scattering time (~2 s) would make the bursts difficult to detect over the radiometer noise. At frequencies near 100 MHz, where low-frequency arrays currently under construction will operate, the predicted scattering time would be on the order of several minutes, and hence would be undetectable.

Lorimer et al.

x

x 0.

1s

Bhat et al.

terrestrial interferencepersistent directions/frequencies

Keane et al.

wide field-of-view -- multiple beams

N beams is equivalent to N telescopes:

- N arrays to maintain in phase- calibration highly direction-dependent, N x effort- N data streams to process and store- N pulsar backends

On-line versus Off-line processing

emission from other strange objects: AXPs, magnetars...

the beam shape

Karastergiou & Johnston 2007profile survey to draw statistical

conclusions of the pulsar radio beam

the beam shape

α

β

geometry info from polarization

lightclosed

openfieldlines

cylinderfieldlines

rotation axis

magnetic axis

radi

o pu

lses

starneutron

radio beam

polarization calibration• unlike dishes, AAs don’t move to point; polarization

calibration highly direction dependent;

• continuous calibration information

• using well understood calibrators inside field-of-view

• very large number of receiving elements, difficult to solve for the instrument response

Hamaker et al.

Important role for simulations in developing calibration techniques - SKADS project using MeqTrees package

(Smirnov, Carozzi, Smits, Levrier)

• polarization usually highest at low frequencies (Suleymanova et al., Mitra et al.)

• high polarization purity can be used for improved timing (van Straten et al.)

• polarization of all types of pulsars as diagnostic for the radio emission mechanism

• polarization to measure RMs, Galactic magnetic

• polarization of all types of pulsars as diagnostic for the radio emission mechanism

• polarization in single pulses changes between two, simultaneously observed frequencies

• continuous or sudden change?

• only the brightest pulsars can be observed in this mode with current telescopes at multiple frequencies (~10). 2 have been published.

Petrova, for theoretical explanations....

multi-frequency observations� pulsar profiles are generally

narrower at higher observing frequencies, up to ~1GHz

� the radio emission mechanism is expected to have some frequency dependence (Melrose 2000)

� Radius-to-frequency mapping; height of emission determined by local plasma density (Ruderman and Sutherland 1975)

Current telescopes sampling discrete frequencies

Low frequency arraysLOFAR, LWA, MWA...

Higher frequency arraysATA, meerKAT, ASKAP?Single dish telescopes

multi-frequency observations• for simultaneous observations: all

instruments should develop protocols for this mode of operation

• standards for pulsar data output: psrfits?

• software for processing: PSRCHIVE?

• synergies with new high-frequency instruments

• polarization usually highest at low frequencies

• high polarization purity can be used for improved timing (van Straten et al.)

• polarization of all types of pulsars as diagnostic for the radio emission mechanism

• polarization to measure RMs, Galactic magnetic field (Noutsos et al.)

• polarization to measure RMs, Galactic magnetic field (Noutsos et al.)

At low frequencies, PA changes faster with

frequency; fine frequency resolution,

high sensitivity

sensitivitypolarization

flexible backends

ISM

• Scattering variability: τ larger at low frequencies; easier to measure?

Hemberger & Stinebring

ISM• Pulsar dynamic spectra

• Holographic imaging can be used to determine the influence of multi-path propagation on pulse arrival time measurements and thus to correct for these propagation delays.

needs narrow frequency channels at low frequency

the last slide

• Raw Sensitivity

• Wide FoV - multiple beams

• Polarization

• Multi-frequency capabilities

• phased arrays; monitoring; ionosphere

• high time and frequency resolution backends, calibration

• new calibration techniques

• pulsar observing/data standards

we want... we need to achieve...