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A real-time transient detection pipeline Using the GSB. Jayanta Roy NCRA – TIFR, Pune, India. @ CASPER 2011 on 12 th October 2011. Collaborators. Matthew Bailes (Swinburne Univ. of Technology) Ramesh Bhat (Swinburne Univ. of Technology) Sarah Burke-Spolaor (ATNF)

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A real-time transient detection pipeline Using the GSB

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A real time transient detection pipeline using the gsb

A real-time transient detection pipeline

Using the GSB

Jayanta Roy

NCRA – TIFR, Pune, India

@ CASPER 2011 on 12th October 2011


A real time transient detection pipeline using the gsb

Collaborators

Matthew Bailes (Swinburne Univ. of Technology)

Ramesh Bhat (Swinburne Univ. of Technology)

Sarah Burke-Spolaor (ATNF)

Jayaram N. Chengalur (NCRA-TIFR)

Peter Cox (Swinburne Univ. of Technology)

Yashwant Gupta (NCRA-TIFR)‏

Jayanti Prasad (IUCAA)

Willem van Straten (Swinburne Univ. of Technology)‏


Transient radio universe

Transient Radio Universe

A major discovery frontier of modern radio astronomy

Astrophysical phenomena on a wide range of timescales

Potential for uncovering new physics and astrophysics

Front runner

X-ray and γ-ray due to multiple wide field-of-view instrument

great success in finding gamma-ray bursts, accreting sources, bursting pulsars

Technological requirements

A = (Sensitivity x Field of View ) needs to be very high

upcoming instruments, e.g. ASKAP, LOFAR, MWA, MeerKAT etc.

Computational requirements

are severe, especially for fast (T << seconds) transients

data need to be sampled at rates ~ 10s s with high frequency resolution

Time scale too short for follow-ups for non-repeating events

e.g. millisecond burst reported near SMC (Lorimer et al 2007, Burke-Spolaor et al 2010)


Slow vs fast radio transients

Slow vs Fast Radio Transients

SN1987A light curve (radio)

A Giant pulse from the Crab pulsar

Cordes et al. (2004)

Turtle et al. (1987)

A “fast” transient

A “slow” transient

  • Slow transients:

    • imaging on wide time integrations : snapshot to daily

  • Fast transients:

    • Timescales ~ seconds or shorter ~ from micro seconds to seconds

    • Time-domain processing at high time and frequency resolution

    • Affected by plasma propagation effects – dispersion, multi-path scattering and scintillation


Transient exploration with gmrt

Transient Exploration with GMRT

A multi-element radio interferometer (30 x 45m dishes) with effective collecting area ~ 3% SKA

Long baselines and sub-array capability provide spatial filtering against impulsive RFIs

Event localization using imaging at a resolution of 5”

Availability of new HPC backend (GSB) with enormous scientific potentials

ability to run multi-subarray beamformer at high time and frequency resolution

ability to capture raw voltage samples from individual antenna at Nyquist resolution

multibeaming across FoV

Interfaced with GPU resources to serve real-time compute requirements

GMRT makes an excellent test-bed for developing the techniques and strategies applicable for next-generation (array type) instruments


A real time transient detection pipeline using the gsb

GSB Schematic

  • Input data rate :

  • 32 antennae x 2-pols base-band analog inputs @ 32 MHz of bandwidth

  • ➤ 2 GSamples/sec (using 16 ADC cards with 4 analog inputs in each card)‏

  • 232 cores Intel Xeon CPUs

  • Each node with 2 GB RAM

  • Dual GbE network interface

  • for input data streaming

  • Dual add-on GbE network interface for high time resolution output data streaming

  • 3.9 Tflops @ 15kwatt

  • Max output streaming ~

  • 3.5 TB/hour

  • Storage : 128 TB

Roy, J. et al., Exp Astron, 2010


A real time transient detection pipeline using the gsb

GSB Specs

  • Simultaneous operation as

    • FX correlatoras an Imaging instrument

    • Beamformeras a Pulsar receiver

  • Input data rate : 2 Gsamples/s

  • Required Compute load : 487 Gflops

  • FFT (181 Gflops )

  • +

  • Fringe rotator ( 8.25 Gflops )

  • MAC (280 Gflops) Beamformer (17 Gflops)

  • Output data rate :

    • MAC output : 4 MB/s

    • Beamformer output : 128 MB/s


A real time transient detection pipeline using the gsb

24 X 7 compute status

Vectorized code (using 128-bit SSE) :with cache optimization and multi-threaded load balancing ensure operation on multiple data elements in parallel on a given physical/logical core

Optimization status :

Required compute load :

490 Gflops

Achieved compute power :

1.5 Tflops

Compute to power ratio :

260 Mflops/watt

Compute to cost ratio :

45 Mflops/USD

Real-time GSB is a highly optimized multi-threaded vectorized parallel pipeline,

working ~ 90% of the theoretical peak Fflops


A real time transient detection pipeline using the gsb

Detecting transients with the GMRT

  • Multi sub-array : trade-off between detection sensitivity and efficiency to reduce

  • false trigger due to RFIs and noise statistics

  • Searching for transients :

    • Dedispersion

    • Event detection by matched filtering followed by thresholding

    • Event identification/association in time and DM

    • Coincidence filtering and candidate selection

    • Event indexer

    • Sending trigger to GSB raw data capture system

  • Event localization using snapshot imaging

  • Detailed time-domain study using multi-pixel phased array beams

Strategy : commensual, 24/7 observing mode

Full raw recording results in 172 TB per day !!


A real time transient detection pipeline using the gsb

Detection sensitivity vs Efficiency of coincidence filtering

A sample data with all spurious event logged

  • For 4 sub-arrays with 5 sigma threshold

  • < 1 events per 20 secs

  • ~ 2000 events per day -> 3 TB of raw

  • data

  • Quasi-simultaneous offline processing +

  • snapshot imaging @ 4x of real-time

  • 100 mJy as detectable flux for 100 ms

  • effective time resolution

  • 10% increase in sensitivity with 2

  • times increase in event rate


A real time transient detection pipeline using the gsb

Discrimination of RFI using coincidence filtering using 4 incoherent (sub-array) beams

  • Discriminate out fast radio transient from RFI

    using DM (= 0) filter.

  • Multiple beam coincidence filter reduces the false triggers due to direction dependent RFI


A real time transient detection pipeline using the gsb

Real-time processing

Proposed scheme: GSB cluster resources for raw data capture + beam generation; additional computing resources for transient processing

GMRT array

GSB cluster

Transient Detector

Trigger Generator

Real-time compute and I/O requirements

Beamformer output @ 512 MB/s for 4 beams with 60 us 512 channel filterbank

Dedispersion and transient search on single 8 core CPU is 15 x of real-time (300 Gflops per beam) !


A real time transient detection pipeline using the gsb

Real-time implementation

  • Simultaneous 4 incoherent beamformer

    • 10% increase in main GSB compute load

    • 1.5 times increase in output network I/O -> 650 MB/s total output I/O, newly

    • added 3 GB/s separate network paths handle all output I/O

  • Dedispersion

    • Processing involves searching over a large range of dispersion measure (DM)

    • need around 1000 trial DMs

    • GPU based dedispersion (for 1000 DMs @ real-time) running on tesla

    • (Ack : Ben Barsdell @ Swinburne)

    • 1 tesla per beam -> 4 CPU host machines work as transient cluster

  • Transient detector

    • Event detection from each of the dedispersed time-series is 20% of the

    • processing load

    • Each beam is processed on 150 Gflops (vector power) i7 CPU host, each

    • equipped with 12 GB memory to hold multiple intermediate data blocks

  • Raw data capture

    • 128 TB storage attached with the compute cluster , capable to flush data @ 5 GB/s

    • 2secs of data buffering in order to accommodate scattered, dispersed pulse at

    • GMRT frequency with moderate DMs


  • A real time transient detection pipeline using the gsb

    Event scrutiny (off-line)

    Detailed off-line analysis can provide event localization within 5” using snapshot

    Imaging and 4x boost in sensitivity for time domain signal characterization


    A real time transient detection pipeline using the gsb

    Case study for PSR B1748-28

    • In beam source PSR B1748-28 is

    • detected in the image plane at an

    • large offset from the phase centre

    • SNR improvement of 2.5x by forming

    • phased array beam towards the pulsar


    A real time transient detection pipeline using the gsb

    Time-domain event scrutiny

    Crab Giant pulse at 4 different frequencies

    Coherent dedispersed giant pulse intensity @

    8 us time resolution

    • Observed maximum dispersion delay of 9.038 sec

    • across the full range 610 MHz to 156 MHz

    • The flux calibration of giant pulses

    • Study of the giant pulse intensity, energies and

    • scattering time distribution


    A real time transient detection pipeline using the gsb

    Multi-pixelization of the FoV for search of pulsed source

    • Simultaneous search over 400 beams using the GSB

      • 4 times improvement in sensitivity

      • 400 times wider search

    • Compute requirements ~

    • Pixelization ~ 5 Tflops

    • FFT cost ~ 170 Gflops

    • Phase centre correction cost ~ 3 Tflops

    • Beam-forming cost ~ 1.75 Tflops


    A real time transient detection pipeline using the gsb

    Multi-pixelization

    A science case : localization of a GMRT discovered Fermi MSP

    (PI : Bhaswati Bhattacharyya @ IUCAA)

    • Current implementation gives 5 phased array beams @ real-time

    • Total no. of beams 16

    • In beam source is localized in the image plane at an offset of

    • 3.75’ X 4’ from the phase centre using imaging followed by multiple beamformers

    SNR improvement of 3 with beamwidth

    reduces from 80’ to 1.4’


    A real time transient detection pipeline using the gsb

    Thank you


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