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 1
2. Once upon a time, in a galaxy far, far away …. 2
3. Once upon a time, in a galaxy far, far away …. 3
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!
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
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]
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
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.
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
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
11. Limit I: Sky limit 11 LEGEND FRATs
12. Limit I: Sky limit 12 LEGEND FRATs (v-1 , v-2 )
13. Limit I: Sky limit 13 LEGEND FRATs (v-1 , v-2 ) Lorimer Keane Thornton
14. Limit I: Sky limit 14 LEGEND FRATs (v-1 , v-2 ) Lorimer Keane Thornton
15. Limit I: Sky limit 15 LEGEND FRATs (v-1 , v-2 ) Lorimer Keane Thornton ATA
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
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
18. 18 Volume limited Simulation Hassall et al. 2013 Thornton, no scattering: 17 per Gpc3 per day
19. Volume limited 19 Assume rate follows star formation (green line)
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
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
22. Backup slides 22
23. Backup: Pulse broadening 23 Pulse broadening of pulsars at 1 GHz. Factor 104.4 more expected at 100 MHz Bhat et al.
24. How far can we observe? Solve for redshift Transfer redshift to distance Assume DMhost =30 pc cm-3
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