Vlbi and Transients Very Long Baseline Interferometry and Pulses


НазваVlbi and Transients Very Long Baseline Interferometry and Pulses
Дата конвертації06.06.2013
Розмір445 b.
ТипПрезентации


VLBI and Transients Very Long Baseline Interferometry and Pulses

Charles J. Naudet

Jet Propulsion Laboratory, California Institute of Technology

April 22, 2013

Outline

  • Overview of the Deep Space Network (DSN)

  • JPL’s Use of VLBI

    • Mission Tracking Support
    • Radio Reference Frame
    • Earth Orientation Parameter Estimation
  • Transients in General

  • Recent DSN Transient Studies

    • GLUE
    • Crab Giant Pulses
    • VLBI transients


JPL’s Interest in VLBI?

  • Why does JPL have a 30+ VLBI program?

    • JPL is responsible for operation of NASA’s Deep Space Network (DSN)
    • Support for Deep Space Missions
    • Positions and velocities:
      • Need accurate tracking and reference frames
      • Must tie reference frames together
        • Planetary and Celestial frames
    • Time: Need accurate clocks and earth rotation data


NASA’s DSN

  • The Deep Space Network, or DSN, is a global network of large antennas and communication facilities that supports interplanetary spacecraft and selected Earth-orbiting missions. In addition it performs radio and radar astronomy observations for the exploration of the solar system and the universe. DSN is part of the NASA Jet Propulsion Laboratory (JPL)



The DSN





NASA Navigation System Accuracy









THE DSN’s TEMPO



Fast Radio Transients

  • Strong Impulsive events ranging from nanoseconds to seconds

  • Known

    • Giant Pulses from Pulsars
      • Only ~ 10 known GP emitters -->
    • RRATS (Rotating Radio Transients)
    • (McLaughlin et, al, Nature, 439,817,2006)
    • Repeating Radio sources, 11 found
    • Detectable via its single pulses,
    • Like slow erratic pulsars
  • Possible

    • Lorimer burst, (Science, 318,777, 2007)
  • Exotics ?

    • Magnetars (J1810-197 pulse of 10 Jy and .15 sec widths, Camilo Nature, 442, 892, 2006)
    • Compact Objects Mergers (Hanson & Lyutikov 2001)
    • GRB Prompt Emission (Paesold & Benz)
    • Cosmic Strings (Vachaspati 2008)
    • Primordial black holes (Rees 1977)
  • Good Summaries

    • CRAFT: The Commensal Real-time ASKAP Fast Transients Survey, http://arxiv.org/abs/1001.2958
    • The Transient Sky, E. Keane ISBN 978-3-642-19626-19627-0
    • Detection of Fast Radio Transients with Multipole Stations, arXiv:1104.4900v1


DSN Transient History

  • GLUE: Goldstone Lunar Ultra-High Energy neutrino experiment

P. W. Gorham, C. L. Hebert, K. M. Liewer, C. J. Naudet, D. Saltzberg, and D. Williams
  • From 1999-2003 a series of experiments were conducted

  • Coincidence experiment of two antennas (DSS14 and DSS13) 22 km apart at Goldstone

  • Dual S-band with L-band off-axis veto capability with ~ 120 hrs observation time

  • 50ns local gate and 150 msec dual antenna gate (set by years range of moon’s geom-delay),

  • 250 msec data record at 1 Gsam/sec

  • Synthesized IF pulse signal calibration, back-end timing ~ 1ns; pulse transmitter and

Limb of the moon for total cross-polarization timing ~ 1 ns. 3c273 for dual antenna timing (~10ns)
  • > 95% livetime, .003 Hz trigger rate



GLUE

  • RFI Noise is critical issue, 70m very sensitive

    • local trigger is easy with a BIC lighter
    • 60 dBi!, unshielded electrical eq. car motors
    • Fluorescent lights, cell phones, TVs, radar, lighting, satelites
  • Lessons learned:

    • Requires multi-antennas, veto
    • multi-bands,
    • dual polarization
  • Goldstone is a on a military base and the impulsive noise can be overwhelming. Even with 22 km separation several days the entire experiment was loss,

    • ~ 100 deadtimes due to RFI
  • Big gates allowed for offline analysis of in and out of time events ( study background)

  • No events above background

  • P. Gorham, K. Liewer, C. Naudet, D. Saltzberg, and D. Williams, (GLUE Collaboration) "Experimental Limit on the Cosmic Diffuse Ultra-High Energy Neutrino Flux", Phys. Rev. Lett., 93, 041101 (2004).



DSN Giant Pulse Search

  • 2008 A small JPL team was formed to search for CGPs

    • (W. Majid, T. Kuiper, S. Lowe, C. Naudet)
  • Why GPs ?

    • Only way to detect extragalactic pulsars
    • Important for understanding the magnetospheres of Pulsars
    • Emission mechanism is not well understood
    • How high energy emission might be linked with radio Emission
    • Conflicting claims on few detections
    • Are GPs restricted to small group of pulsars or many waiting to be discovered
    • Galactic pulsar population may be larger than we thought
    • Wide range of single pulse properties apparent
    • Algorithms relevant to transient detection phenomenon
  • Current study to look for GP Correlation with high energy emission. One way to pin-point the origin of GP emission.



DSN Giant Pulsar Search



Noise Statistics



Crab Phase-Time Plots



Pulse Morphology



Crab GP Energy Isotherms



Crab GPs

  • To date

  • L-band: 15 exp: 42 hours, ~ 45K GPs, ~.29 per sec

  • S-band: 1 exp: 3.75 hours, ~ 1800 GPs, ~.13 per sec

  • X-band: 4 exp: 16 hours, ~ 383 GPs, ~.006 per sec

  • Majid,Naudet,Lowe,Kuiper, APJ, 741, 2011,

  • ~60 hours of data  ~ 50 Tbytes of disk space

  • Total reprocessing time on current machine ( 16 threads) ~ 2 week

  • Current Rule of Thumb: 1 hr of data needs 1 TB and 6 hrs of cpu for 1 DM

  • RFI : Only a handful of seconds per experiment need to be removed

    • Ave and rms power calculated every sec for data assessment
    • Near antenna on / off source.
    • DM of 56 pc/cm3 solves most of RFI problems
    • Caution in calibration: modulated diodes, Phase Calibration Tones


Noise



Surveys

Due to small amount of fast transients a diversity of search parameters is very important

Transients programs growing leaps and bounds
  • Past Surveys (see details in VLBA paper arXiv:1104.4900v1)

    • ATA Fly’s Eye (von Korff et al. 2009)
    • LWA transients study (Taylor et al. 2006),
    • LOFAR transient campaign (Hessels et al. 2009),

New surveys coming on line will set the bounds on rates !
  • CRAFT (Johnston et al. 2008), Murchison Widefield Array (MWA) (Lonsdale et al.2009), and MeerKAT (Jonas 2009)

  • Nice VLBA paper: V-FASTR limits arXiv:1205.5840v1

    • 1300 hours from 327 MHz -86 GHz. (112 hours at S-band)
    • No single-pulse events found
  • Current Efforts: ( via CRAFT paper)

    • Freq Time Res Sensitivity (1s) Baseline Starting
  • Parkes 1.4 GHz 64 ms 1.5 mJy NA 9/2009

  • VLBA .6-.9 GHz 2-10 ms 5.6 mJy 200 - 8600 km 2/2010

  • GMRT .3-.6 GHz 32 ms 22 mJy NA done

  • LOFAR .12 GHz 50 ms 40 mJy 1000 km 2010

  • JPL 2.2 & 8.3 GHz .2 -- 35ms 18 mJy 10000 km 2012



Looking for Transients in JPL’s VLBI Data

  • Use JPL Operational VLBI for Transients searches (no $$$)

    • 34m ant (FWHM=.24 degrees), S/X-band,
    • Over 100-200 hours a year, Multi-year future, long term monitoring
    • Full sky, ~500 sources, repetitive
    • Apply GP matched-filter at both antennas individually.
    • Apply VLBI clock offsets and total geometry delay corrections then coincidence
    • For proven transients full correlation  astrometric information
  • But

    • Must be NIB (non-interference basis)  Must Filter PCGs
  • Problems

    • Data logistics
    • CPU intensive
    • All transient surveys must show events are not of terrestrial origin and all are very sensitive to impulsive RFI
    • RFI mitigation is a challenge for all teams.



Phase 1: Shake out
    • CPU and Disk space limitations
    • Incoherent dedispersion ( min pulse width ~.2ms)
    • Limit DM search from 0 to 500 pc/cm3
    • Set SNR cut high enough to inspect all Candidates manually (~ 1 candidate hit/hr )
    • Require clean and clear Frequency-Time plots
    • Develop RFI diagnostics plots
    • RFI removal techniques



Status

  • Phase 2 (starting now)

    • Install new CPU with 75 Tbytes disk space
    • Reduce SNR thresholds in incoherent dedispersion searches
    • Increase DM search range 0 to 2000 pc/cm3
    • Save all dual hit candidates and reproprocess with coherent dedispersion
    • Use new VLBI DVP recorder ( allow full bandwidth, 100 MHz at S-band)
    • Negotiate adding in a Giant Pulsar cal source once per track
    • RFI Mitigation improvements. Algorithms development
    • Increase search space to msec  seconds  minutes


Related JPL Efforts

  • Study of Electrical Activity in Martian Dust Storms with the Deep Space Network antennas

  • Current effort is being made to implement a real time transient detector for all the IFs and antennas in the DSN



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