Searches for millisecond radio bursts

Duncan Lorimer
LOFAR and the Transient Radio Sky, Amsterdam, December 2008

Transcript

1. Duncan Lorimer (WVU/NRAO) Searches for ms radio bursts * background and history * a bright new source * puzzles and sleepless nights * searches of archives * future directions
2. Previous radio transient searches •  Discovery of pulsars •  Giant pulses from some pulsars •  Searches through pulsar survey data •  Targeted searches of other galaxies –  e.g. Linscott & Erkes (1980) -> M87
3. Reasons for lack of success? •  Narrow band observations –  Low immunity to interference? •  Only single beam on sky –  Harder to gauge reality? •  Lots of output to sift through –  Much human intervention required? •  There’s not much out there! –  Pulsars are easier to find and study, particularly as periodic sources Discovery of RRATs in 2005 breathed new life into subject…
4. Manchester et al. (2006) ApJ 649 235 209 x 2.3 hr pointings = 20 days 1 ms sampling 288 MHz bandwidth 14 pulsars discovered in standard periodicity search (FFT) What about single pulses? Parkes Magellanic Cloud survey Began reprocessing data to look for dispersed pulses in Fall 2006. Motivation: look for giant-pulse-ers and RRATs
5. A known pulsar in the LMC
6. A strange new source? Lorimer et al. (2007) Science 318, 777
7. A strange new source? Measure DM to high accuracy 375(1) cm-3 pc Measure S ~ 30 Jy Measure W~f-4.8(4) Measure S~f-4.3(12) FWHM 5 ms unresolved!
8. The burst localized on the sky Left - SMC and PM footprint from discovery paper. Top - Kulkarni et al. Confine location to within elongated polygon of size 14 arcmin2
9. •  Astrophysical in origin –  Cold plasma dispersion law and W~f-4.4 •  Not a Galactic object –  DM = 375 cm-3 pc •  Very very unlikely to be in SMC/halo –  Offset position + far higher DM •  An extragalactic object –  DM ~ 1200 x z implies z < 0.3 !!! –  Crude estimate gives D = 500 Mpc. What is the burst’s nature?
10. •  Energy budget (@ 500 Mpc) –  Radio energy output ~ 1040 erg –  Brightness temperature ~1039 K •  Implied event rate –  1 burst seen per 20 day with PKS –  Hundreds per day over whole sky… –  0.4 per day per Gpc3 •  Possible sources –  GRB? NS-NS coalescence? Sne? –  (PBH E~1035 erg) What is the burst’s nature?
11. •  Extant PKS data should contain more –  Will better constrain the rate •  Forthcoming radio telescopes –  LOFAR –  ATA •  Search GW data –  Position and time localized…. •  A new cosmological probe??? –  Measurement of IGM… dark matter? Implications/predictions
12. Absence of weaker events? §  dN/dS ~ S-a implies more fainter sources in survey §  Sky coverage is flux dependent, S=30 Jy gives 5 deg2
13. Absence of weaker events? §  dN/dS ~ S-a implies more fainter sources in survey §  Sky coverage is flux dependent, S=30 Jy gives 5 deg2 §  For Gaussian beam, solve dN(obs)/dS = const * ln(S/Smin) S-a a=1.0 a=2.0 a=2.5
14. Archival data should contain more §  Burke-Spolaor & Bailes -> Swinburne PM surveys §  Crawford -> PM EGRET survey §  Lorimer et al -> Parkes high-latitude survey §  Events found, but not really the ones we “wanted” to see…
15. •  New bursts with DMs 220-400 –  One very close to 375! •  New bursts have different properties –  Seen in all 13 beams –  Inverted spectral properties –  Inverted pulse broadening properties –  No known terrestrial transmitter Cosmic conspiracy? Current working hypothesis: confidence in astrophysical origin of original burst suffered a major hit. Urgently need more examples if we are to believe this is truly astrophysical.
16. •  Complete reanalysis of archival data –  Revise limit on event rates (50/day/sky) •  Routinely search current surveys –  Parkes, Green Bank, Arecibo •  Initiate wide-field monitoring projects –  LOFAR –  ATA –  KAT –  ASKAP –  GERTIE… Next steps
17. •  Counterparts with other instruments –  Electromagnetic and Gravitational •  Probe of intergalactic medium –  Electron density, Faraday rotation –  Missing baryons? •  New cosmological probe? –  Population of standard candles? –  Need to identify a counterpart! Key factors: localization and rapid alert Potential pay-offs