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The DiFX software correlator

The DiFX software correlator. DiFX is an FX style correlator written in C++ Designed to run on commodity clusters Optimised Intel vector libraries are used for good performance Makes hard-to-reach areas of correlator parameter space accessible

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The DiFX software correlator

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  1. The DiFX software correlator • DiFX is an FX style correlator written in C++ • Designed to run on commodity clusters • Optimised Intel vector libraries are used for good performance • Makes hard-to-reach areas of correlator parameter space accessible • Now used by LBA, VLBA and (soon) AuScope, MPIfR (Bonn)

  2. DiFX at the VLBA • Acceptance testing is all but complete - correlator switchover by end of year (call for proposals already made in October) • Investment has been modest: 10 node cluster costing ~$25,000 enables throughput of ~500 Mbps/antenna for 10 stations (roughly double the hardware correlator)

  3. VLBA DiFX verification Visibility phase vs time:Colors are a little hard to see: blue is HWC, purple is SWC, cyan is where they overlap perfectly

  4. New VLBA functionality: now • Much increased spectral and temporal resolution: in principle almost infinite, in practice at least 16x previous is offered • Much more flexible pulsar processing; previously only an on/off gate available • Ability to process data in previously inaccessible formats (like the higher datarate Mark5B/B+)

  5. Future features: Multiple PCs • At any given instant, the phase centre (PC) of correlation can be changed by rotating the visibilities by a phase value equal to the sky frequency x delay (between desired phase centre and current phase centre) • When done in-correlator,very high spectral andtemporal resolution meansalmost no smearing primary beam uv-shifted “pencil” fields

  6. Future features: Multiple PCs • At low frequencies (and high sensitivity) there will be many sources per primary beam • Thus a dramatic improvement in survey speed! • Applications in in-beam calibrator searches, star-formation regions, galaxy evolution studies and more

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