1. Fast radio bursts and the magnetization and turbulence of the cosmic web Ryan Shannon, ICRAR-Curtin/ATNF (Vikram Ravi, Swinburne Pulsar Group)

2. Outline Fast radio bursts (FRBs) –Exciting times! FRB 131104 –The (improbable/real-time) discovery of an FRB to the Carina dwarf spheroidal –Unusual radio-continuum variable FRB 150807 (re-submitted to Science today) –Bright –Polarized –Implications for magnetization and turbulence of cosmic web

3. Fast Radio Bursts (FRBs) Discovered in pulsar surveys as highly dispersed, short, bright single pulses of radio emission Surprisingly frequent, but infrequently detected –2000 – 6000 per day (e.g., Keane & Petroff 2015) –17 published (16 Parkes, 1 Arecibo, 1 GBT) New unprecedentedly bright radio emission –Cataclysmic explosions –Germane pulsar emission If cosmological, opportunity to probe diffuse intercluster plasma –Find missing baryons (via electrons) –Study intergalactic plasma –With polarisation (rotation measure), study magnetic field of Universe

4. A repeating FRB Repeat bursts from the Arecibo FRB (121102) Wildly variable spectral inde Pulses seen at Arecibo and Green Bank (2 GHz) No obvious periodicity in the pulses –Fast rotation? –Magnetar-like emission? No localization or concurrent emission at other wavelengths Not detected with interferometer (VLA campaign ongoing) (Spitler et al. 2016)

5. An FRB with an afterglow FRB 150418 (Keane et al. 2016) Fading radio source discovered with ATCA and coincident with FRB Host galaxy of radio afterglow identified (z ~ 0.5) Consistent DM-z relationship –“solved” missing-Baryon problem Subsequent observations have shown that source has re-brightened –Intrinsic variability –Scintillation –Still an unusual source (Vedantham et al. 2016), but not a classical radio transient

6. Open questions Are FRBs real? Doing more and more astrophysical things Do they repeat? At least one of them Where do they come from (local, extragalactic, cosmological)? Extragalactic-cosmological What causes them? (Stars, pulsars, something more exotic?) How many (gulp) classes? (Are repeating and non-repeating FRBs caused by the same thing) Can we use them to meaningfully study the intergalactic medium? Need to tease out host and Milky Way contributions How do we find more/increase yield? (Wide-field) How unique is the (first) Lorimer burst? (Still the brightest, but not by as much)

7. A FRB Toward the Carina Dwarf Spheroidal Targeted surveys for FRBs with Parkes MB Searched dwarf spheroidal galaxies for pulsars at the same time Within 1.5 hours of starting searching, discovered FRB131104 Real time FRB (Ravi, Shannon & Jameson 2015) Tidal ellipse of galaxy FRB detected in this beam Parkes 13-beam multibeam receiver

8. FRB 131104 Galactic latitude ~ 20 o DM ~ 780 pc cm -3 DM sweep and scattering consistent with astrophysical plasma Narrow: –Intrinsic burst width is < 100 microsecond Lumpy but relatively flat spectrum No repeats in 100 hr of follow up observations

9. FRB afterglow? –Real time detection -> search for slow transients with ATCA in 4cm band –One variable source (of ~ 20 sources) identified in field coincident with FRB position –Initially brightens quickly/and hardens Some similarities to GRB afterglows (Frail et al. 1998) –Modest rebrightening after 300 d –Rare variable/radio transient (Bell et al. 2015, Moolay et al. 2016) (< 2%?) –Rate problem: can all FRBs produce afterglows? Frail et al. 1998 200 d

10. 10 arcsec 1 arcsec Optical counterpart Arcsecond localization enabled search for optical counterpart with with Gemini-South (8-m time in the south) One of the sources is detected in infrared with WISE –AGN (based on WISE colours) Source in a close pair (< 0.7 arcsec) –30 Mpc projected separation at z ~ 2 –Chance coincidence of this is weird? Gemini spectra obtained but seeing poor The mystery continues

11. Time (s) Freqeuncy (MHz)

12. Discovered while timing millisecond pulsar J2241- 5236 (b ~ 55) Low DM (for FRB) –265.5± 0.1 pc cm -3 –(Pulsar in field: 11 pc cm -3 ) Bright: –Two beam detection -> correct for attenuation –120 Jy (average) –> 1.1 kJy in individual scintles Highly linearly polarized: –RM 12 ± 1 rad m -2 –Nearby pulsar: 13 ± 1 rad m -2 (all RM is Galactic) Flux modulation: two scales –Narrow: outside of the Galaxy –Broad scale: Scintillation/Refraction/ESEs? FRB 150807

13. Localization of FRB 150807 No ATCA variable/transient (suboptimal config) VISTA sources (deepest optical survey of field) –3 (main sequence) stars –6 galaxies –Brightest galaxy: elliptical/lenticular –z photo ~ 0.2 -0.4 –95% probability that z > 0.125

14. Implications for the cosmic web Redshift > 0.12 (distance > 500 Mpc) –FRBs occur at cosmological distances Low RM -> non magnetized plasma – < 18 nG Most of DM is extragalactic (not magnetized) DM consistent with z ~ 0.25 Narrowband scintillation -> IGM? –Scattering measure (level of turbulence): 10 -13 Gpc m -20/3 –In ballpark of predictions (Macquart & Koay 2013)

15. Conclusions FRB 131104 –In direction of Carina Dwarf Spheroidal, but unlikely related –Variable radio counterpart found, associated with optical pair –Need spectrum to better understand association (or lack thereof) FRB 150807 –Bright FRBs aren’t uncommon –Wide-field surveys should find heaps –Where are the low-frequency FRBs? –Multiple beam detection provides improved direct localization –Potential probe of intergalactic magnetization and turbulence

16. Modelling the multibeam response Physical multi-frequency model of receiver response Include coma, blockage from focus cabin Don’t model coupling between individual feeds Use observations of bright pulsar to test model

17. Modelling the multibeam response Position Response (dB) Red: Data Blue: Model Conclusion: model adequate Use relative flux versus frequency to localize and solve for “primary beam attenuation”

18. Rotation measures Comparison of RM of FRBs to those of galactic pulsars Extragalactic RM contribution much lower than that observed in Galactic plasma

19. Scattering-DM relationship for FRBs Some (but not all) FRBs are under-scattered compared to the relationship found in our Galaxy (i.e. Bhat et al. 2004). Scattering in the host and in our galaxy have the same effect on the pulse.