transient cosmic phenomena and their inï¬‚uence on the design

Parameter space Discovering phenomena ASKAP & the SKA The digital age

Transient Cosmic Phenomena and their Influence

on the Design of the SKA Radio Telescope

Research Review

Tim Colegate

Curtin Institute of Radio Astronomy

5 May 2009

Transient Cosmic Phenomena and their Influence on the Design of the SKA Radio Telescope Tim Colegate


ToC

Parameter space

Discovering phenomena

ASKAP & the SKA

The digital age



PhD objectives

! Compendium of time-domain phenomena! Enabling technological factors to fully explore the

time-domain parameter space! Transient capability of the SKA and other arrays! Integrate results into the SKA performance and cost

modelling effort



Transient cosmic phenomena - the hightime resolution universe

! Dynamic radio sky is poorly understood! First steps are rare but bright events with pulse-like emission

! Lorimer-type extra-galactic bursts, giant pulses etc.! No guarantee of periodicity

! Not explicitly an SKA Key Science Project, but there is:! A growing interest in the transient universe! A desire to explore the unknown! Serendipity!

! We have a generally accepted idea of how to build a “good”synthesis imaging telescope...

! Can the same be said of a high time resolution aperture synthesistelescope?



Parameter (phase) space

Cosmic Discovery(Harwit, M., 1981)

Phase space ofE-M observations

! Spectral frequency! Spectral resolution! Temporal resolution! Angular resolution! Polarisation! (Intensity)

Assumes that positionalinformation is unimportant! Figure: Properties of a photon: frequency, time,

angular direction, spatial position and spin (adaptedfrom Harwit, 81).



Filtering the observational parameter space

! We want to exploretemporal resolution;

and possibly spectral

resolution! Wavelength limited by

instruments! Pulse-like phenomena -

consider event rates! Point sources, so high

angular resolution notadvantageous for detection

! Event rate search space:FoV + observing time Figure: Phase space filter. Small shaded cube is

what the instrument dectects (source: Harwit, 81).



Harwit: Analysis vs DiscoveryFor a single pulse, these need to occur simultaneously!

! Analysis! Detailed information

! Discovery! Explore parameter space

Figure: Applying filters to the observational parameter space (source: Robinson, 87)



Monitoring the sky

! Event rates! Field of View +

observing timeincreases likelihoodof dectection

Figure: Telescopes overlaid onminimum detectable flux density vs.instantaneous solid angle (SKAMemo 97, Cordes 08)ν0 = 1 GHz, BW = 300 MHztint = 1 sec, ηa = 0.6, Tsys = 25 K



The which with what and how?



ASKAP observational strategy

Searching at ∼ ms time resolution with a wide FoV, but also goodverification and localisation

! Incoherent search with triggered coherent buffer! Incoherently sum 36 ASKAP antennas

! 6 x sensitivity, 30deg2 FoV! Data streams scale with number of PAF primary beams! Inherently flexible - throttle data rate: tsamp , Nchannels , Nbits , Nbeams ,! Still many real-time challenges!

! Rolling buffer PAF primary beam voltages! Allows for analysis of event at full sensitivity

! Excellent for commensal observing! Within similar regions of the sky, any pointing is as good as any other?! Large observed volume of sky



SKA observational strategy

! Expecting a dense core of dishes! Searching the primary FoV

! Pixelise the FoV with tied-array beams! Scale as FoVexpansion

(

b

D

)2

! Note the inefficiencies for ASKAP!

! Snapshot imaging! High correlator dump-rate! Sky pixelisation still required

! Search on each pixel! Comensal observing possible?

Figure: Pixelising the primary FoV withtied-array beams (SKA Memo 97, Cordes07). Also see Smits et al, 09.



Why ASKAP?

! SKA Pathfinder! Event verification - only one chance!! Radio frequency interference excision! Novel experiments? Weighting on the PAF beamformer?

Numberdishes

Relativesensitivity

RelativeFoV

Incoherent ASKAP 36 0.21 78.8Correlated ASKAP 7 0.23 78.8Correlated ASKAP 36 1.25 78.8

Table: Relative sensitivity and FoV compared to Parkes MB (assumingsame Tsys, aperture efficiency etc.)



Realities

Bottlenecks! Data transport

! How soon can we get itoff-site?

! Real-time processing! Searching for the unknown

can be very intensive

! Storage capability! We have the space, but can

we get it onto disk?

! Power! Over-arching concern for

any activity on-site

Questions to be answered! Where can we take shortcts

or make tradeoffs?! Limiting our parameter

space search in differentdirections

! Is an “incoherent telescope”best for the near future?

! Where does Moore’s lawfail us?

! How do we not design outcertain features?



SKA performance and costing tool

Relevance of the tool! Dish based models

! Preliminary SKASpecification Process (SKAMemo 100)

! Aperture array models! SKA Design Studies

program

! New version of tool underinitial use by SKADS andsome engineers in the SKAProgram DevelopmentOffice

Using the tool! Tool has use in the design

stage of the SKA! Operational decisions yet to

be made (esp. power)! Identify bottlenecks and

limitations of the system



The path ahead

! Use ASKAP and other pathfinder telescopes as case studies! ASKAP Survey Science Projects is a useful process

! Sept 09 - extended (∼9 month) Manchester visit! Interaction with engineers at the SPDO! Further development of cost tool! European thinking on transients

! Exercise costing tool for insights on SKA design and operationalconsiderations for high time resolution science

! Show path for ASKAP and SKA as a credible transient telescopes! Write it up!


transient cosmic phenomena and their inï¬‚uence on the design

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