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A limit on FRBs from FRATs observations

transientskp
January 09, 2014

A limit on FRBs from FRATs observations

Sander ter Veen

transientskp

January 09, 2014
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  1. A limit on FRBs from FRATs
    observations
    Sander ter Veen
    Radboud Universiteit Nijmegen
    Emilio Enriquez, Heino Falcke, Jörg Rachen, Anya Bilous and the Pulsar Working Group
    1

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  2. Once upon a time, in a galaxy far, far away ….
    2

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  3. Once upon a time, in a galaxy far, far away ….
    3

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  4. Fast Radio Bursts (FRBs)
    Highly dispersed bursts => Extra-galactic origin
    Non-repetitive
    4
    Lorimer et al. 2007, first FRB
    Keane et al. 2011, possible FRB
    Thornton et al. 2013, 4 more FRBs!

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  5. The FRATs project
    •  Searching for Fast Radio Transients:
    dispersed millisecond pulses
    •  Commensal wide incoherent stokes
    beam (11 deg2 @ 150 MHz)
    •  Real-time trigger
    •  Identification using raw data from
    Transient Buffer Boards (next Talk by
    Emilio)
    5

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  6. FRATs: Detection of dedispersed pulses
    •  Dispersed ms pulses
    •  Dedisperse in 5 frequency bands
    •  Coincidence between bands
    –  RFI rejection 99.9%
    •  400 Trial DM values Real-Time in
    current LOFAR hardware
    ∆tDM
    = 4.15 ms DM(
    1
    v2
    1,GHz

    1
    v2
    2,GHz
    )
    120 MHz
    150 MHz
    145 MHz
    140 MHz
    135 MHz
    130 MHz
    125 MHz
    0.0 1.0 2.0 3.0 4.0
    Time [seconds]

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  7. FRATs: Detection of dedispersed pulses
    •  Dispersed ms pulses
    •  Dedisperse in 5 frequency bands
    •  Coincidence between bands
    –  RFI rejection 99.9%
    •  400 Trial DM values Real-Time in
    current LOFAR hardware
    ∆tDM
    = 4.15 ms DM(
    1
    v2
    1,GHz

    1
    v2
    2,GHz
    )
    120 MHz
    150 MHz
    145 MHz
    140 MHz
    135 MHz
    130 MHz
    125 MHz
    0.0 1.0 2.0 3.0 4.0
    Time [seconds]
    1.0 2.0 3.0 4.0
    Time [seconds]
    Power [a.u.] with offset
    Dedispersed timeseries

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  8. First observations
    8
    Property Value
    Incoherent beams 3
    Coherent beams 219
    Frequency Range 119-151 MHz
    Pointing duration 1 hour
    Stations Superterp (6 stations)
    Pointings in cycle 0 200
    Frequency resolution 12 kHz
    Time resolution (FRATS) 2 ms
    Search width 2, 4, 8, 16 ms
    This presentation 35 pointings
    Sky coverage 1360 deg2 hours
    Fluxlimit 93-152 Jy
    DM range 5-110 pc cm-3 (400 Trials)
    •  Triggering real-time with
    LOFAR Tied-Array All-
    sky Survey (LOTAAS)
    •  Using incoherent beam
    for large field of view
    •  Check if triggered pulse
    looks physical
    •  Trigger Transient Buffer
    Board data for position
    and to check for celestial
    origin.

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  9. Results
    4 (candidate) pulsars in all analysed LOTAAS pointings
    Some non-dispersed events (see next talk)
    No FRB candidate
    Set limit by integrating:
    •  Time on sky
    •  Beam size
    •  Sensitivity
    •  DM range
    9

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  10. Beamsize and sensitivity
    •  Beamsize and sensitivity both
    depend on elevation
    •  Beamsize= π/4 FWHM2 sin(EL)
    •  SEFD * ΔDM * sigma / sin(EL)1.4
    •  7.5 Jy / 0.75 * 7 / sin(EL)1.4
    •  70 Jy / sin(EL)1.4 (@ 2ms pulse)
    •  Fluency 140 Jy ms (@ 2ms pulse)
    Time on sky: analysed in chunks of
    3-10 minutes, reduced by dataloss
    for dedispersion length
    SEFD ~ sin(EL)1.4 Aris Noutsus
    10

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  11. Limit I: Sky limit
    11
    LEGEND
    FRATs

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  12. Limit I: Sky limit
    12
    LEGEND
    FRATs (v-1 , v-2 )

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  13. Limit I: Sky limit
    13
    LEGEND
    FRATs (v-1 , v-2 )
    Lorimer
    Keane
    Thornton

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  14. Limit I: Sky limit
    14
    LEGEND
    FRATs (v-1 , v-2 )
    Lorimer
    Keane
    Thornton

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  15. Limit I: Sky limit
    15
    LEGEND
    FRATs (v-1 , v-2 )
    Lorimer
    Keane
    Thornton
    ATA

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  16. How far can we observe?
    Observed maximum DM
    χe
    = ionization factor
    Transfer redshift to distance
    Assume DMhost
    =30 pc cm-3 =>
    Probe 30% of galaxies compared
    to DM=100 pc cm-3, lower
    expected rate, not taken into
    account yet
    DM⊥ = 30

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  17. Volume limit
    17
    Integrated volume, limit
    Expected 17 per Gpc3 per day
    no scattering limit, Thornton only
    Simulations by Hassall et al. 2013
    Preliminary

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  18. 18
    Volume limited
    Simulation Hassall et al. 2013
    Thornton, no scattering:
    17 per Gpc3 per day

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  19. Volume limited
    19
    Assume rate follows star formation
    (green line)

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  20. Expected rate
    20
    LEGEND
    FRATS (v-1 , v-2 )
    Thornton volume
    Thornton SFR
    DMmax
    =110
    DMmax
    =500 Assumptions:
    8.5 events per
    Gpc3 per day
    with the
    brightness of
    the 2nd brightest
    Thornton burst
    Selection z>0.05
    Preliminary

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  21. Conclusions and Outlook
    FRATS has been searching in real-time for millisecond pulses for over a year
    Apart from a few pulsars, no single bright bursts have been found
    We set an upper limit on the FRB rate of
    <103 per sky per day up to a DM of 110
    Or
    <10000 per Gpc3 per day (compared to 17 per Gpc3 per day measured)
    Considerations Volume limit and Star Formation Rate.
    Observations continue, searching up to a DM of 500
    One event expected per 7 (VOL) / 33 (SFR) days if spectral index of -1 (and 3
    beams)
    Cycle 1 commensal observing proposal approved and starting up
    21

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  22. Backup slides
    22

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  23. Backup: Pulse broadening
    23
    Pulse broadening of pulsars at 1 GHz.
    Factor 104.4 more expected at 100 MHz
    Bhat et al.

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  24. How far can we observe?
    Solve for redshift
    Transfer redshift to distance
    Assume DMhost
    =30 pc cm-3

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  25. Galaxy exposure
    From the disk you can see on average (πr2/2) / (2r)(2r) = π/8 =40%
    DMmax
    =100: From the disk you can see 1-(40*60/2)/(60*100) =80%
    25

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