A limit on FRBs from FRATs observations

Sander ter Veen

Transcript

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
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2. Once upon a time, in a galaxy far, far away ….
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3. Once upon a time, in a galaxy far, far away ….
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4. Fast Radio Bursts (FRBs)
   Highly dispersed bursts => Extra-galactic origin
   Non-repetitive
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   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)
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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
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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
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11. Limit I: Sky limit
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    LEGEND
    FRATs
    

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12. Limit I: Sky limit
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    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
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    Assume rate follows star formation
    (green line)
    

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20. Expected rate
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    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
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22. Backup slides
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23. Backup: Pulse broadening
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    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%
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