1. Models for Fast Radio Bursts & Future Astrophysical Tests
Zigao Dai
School of Astronomy and Space Science, Nanjing University
Collaborators: Jie-Shuang Wang, Yuan-Pei Yang,
Xue-Feng Wu, Yun-Wei Yu, Fa-Yin Wang, Yong-Feng Huang
2nd SVOM Pingtang, Guizhou, Apr 2017

2. Outline Properties of FRBs Some special FRBs Energy source models
Prospects & summary

3. Outline Properties of FRBs Some special FRBs Energy source models
Prospects & summary

4. FRBs are ms-duration flashes of GHz emission.
FRB was discovered by Lorimer et al. (2007).
More FRBs (total 21 up to now) have been detected (Thornton et al. 2013; Keane et al. 2012, 2016; Burke-Spolaor & Bannister 2014; Spitler et al. 2014, 2016; Champion et al. 2015; Masui et al. 2015; Petroff et al. 2015; Ravi et al. 2015).
Lorimer et al. 2007, Science, 318, 777

5. Propagation effects
The frequency-dependent refractive index of a cold, ionized plasma means that any signal propagating through it is dispersed. Emission at frequency ν (in MHz) delays with respect to emission at infinite frequency by ΔtDM (in s)
As the dispersive delay depends only on the number of electrons along the line of sight, and not their distribution, the dispersive delay follows the same ν−2 law in the ISM and the IGM.

6. Cosmological sources?
Thornton et al. 2013, Science, 341, 53

7. Catalogue of 18 FRBs
FRB Parkes

8. Sky Distribution
Caleb et al. 2017, arXiv:

9. Distributions of DM and Energy
L. B. Li, Y. F. Huang, Z. B. Zhang, D. Li & B. Li 2016, arXiv:

10. Extremely high brightness temperature: coherent emission
1037 K

11. Summary: properties Intrinsic durations: Characteristic frequency:
Dispersion measure:
Fluence:
Brightness temperatures:
Frequency dependent delay:
Frequency dependent width:
Burst rate:

12. Outline Properties of FRBs Some special FRBs Energy source models
Prospects & summary

13. FRB 150418: Afterglow or AGN flare?
Keane et al. 2016, Nature, 530, 453:
host galaxy, z=0.492±0.008
Williams & Berger 2016;
Vedantham et al. 2016

14. FRB 121102: First repeating FRB
Spitler et al. 2016, Nature, 531, 202

15. Implications Classification ─ Repeating FRBs ─ Non-repeating FRBs
GWBs/FRBs/short GRBs (triplets)

16. Outline Properties of FRBs Some special FRBs Energy source models
Prospects & summary

17. Energy source models related to NSs
Magnetar giant flares (Popov & Postnov 2007; Kulkarni et al. 2014)
Giant pulses from young pulsars (Connor et al. 2015; Cordes & Wasserman 2016; Pen & Connor 2015)
Giant-glitch-induced events in young magnetars (Lieu 2017)
Pulsar lightning (release of stored electrostatic energy, Katz 2017)
Planetary companions around pulsars (Mottez & Zarka 2014)
Collapse of supra-massive NSs into black holes (Falcke & Rezzolla 2014; Zhang 2014; Ravi & Lasky 2014)
Neutron star-white dwarf binaries (Gu et al. 2016)
Binary neutron star mergers (Totani 2013; Wang et al. 2016)
Pulsar-asteroid collisions (Geng & Huang 2015; Dai et al. 2016)

18. Other energy source models
Cosmic string collisions (Cai et al. 2012)
Flaring stars (Loeb et al. 2014)
Binary white dwarf mergers (Kashiyama et al. 2013)
Black hole-neutron star mergers (Mingarelli et al. 2015)
Evaporation of primordial black holes (Barrau et al. 2014)
Charged black hole mergers (Zhang 2016; Liu et al. 2016; Punsly & Bini 2016)
Light sails of extragalactic civilizations (Lingam & Loeb 2017)
Collisions between relativistic field structures (Thompson 2017)
Pulsar’s magnetosphere combed by a plasma stream (Zhang 2017)

19. Final inspiral of two neutron stars
E = vB/c
Wang, Yang, Wu, Dai & Wang 2016, ApJL, 822, L7

20. Constraint on Distance a

21. FRBs from NS-NS final inspiral
Current event rate of FRBs

22. Triplets: GWBs, FRBs and SGRBs
Fernández & Metzger (2016)
Dai & Lu 1998, PRL, 81, 4301; Dai et al. 2006, Science, 311, 1127

23. Romeo & Juliet never forsake with each other!
在天愿作比翼鸟，在地愿为连理枝。 In sky, we’d be two birds flying wing to wing, and on earth two trees with branches twined from spring to spring。 天长地久有时尽，此恨绵绵无绝期。 But, the boundless sky and endless earth may pass away. This regret shall last for evermore. ——BAI Juyi (白居易, 806)

24. Black dotted circle: R-band
Black dashed circle: Radio
Blue dashed circle: Gamma-ray
Red solid circle: Radio + Gamma-ray
X1 & X2 squares: Two quasars
T90 ~ 377 s, Eγ ~ 51051 ergs for z ~ 0.55
Signal to noise: 4.2σ confidence

25. Follow-up X-ray & optical observations
DeLaunay et al. (2016)

26. Follow-up radio observations with ATCA26
Shannon & Ravi (2016): no radio afterglow but variable radio source of an AGN, which suggests that the gamma-ray transient may be from this AGN.
However, its duration is much smaller than that of the AGN’s flare.

27. Constraint on n from Observations
n  10-4 cm-3
Gao & Zhang (2016); Dai, Wang & Wu (2016)

28. Constraints on Postmerger Pulsar
Dai, Wang & Wu (2016)

29. Fully general relativistic magnetohydrodynamic simulations of binary neutron star mergers: stable millisecond magnetars (Giacomazzo & Perna 2013, ApJL)

30. Summary for FRB
n  10-4 cm-3 → binary NS merger (Dai, Wang & Wu 2016; Gao & Zhang 2016)
T90 ~ 377 s → long-lasting central engine
Implications: (1) [Lγ, T90, εγ] → ms magnetar;
(2) GW event: inspiral, merger, & spin-down (Dai, Wang & Wu 2016)

31. Repeating FRB models
FRB rules out catastrophic events, flaring stars, and giant flares from magnetars (Spitler et al. 2016)
Giant pulses from young pulsars (Connor et al. 2015; Cordes & Wasserman 2016; Pen & Connor 2015)
NS-white dwarf binaries (Gu et al. 2016)
Highly magnetized pulsars encountering asteroid belts of other stars (Dai, Wang, Wu & Huang 2016)

32. The comet-Jupiter impact 16-22 July 1994
Comet Shoemaker-Levy 9: 21 fragments

33. Encounters of pulsars/asteroid belts
Dai, Wang, Wu & Huang 2016, ApJ, 829, 27
Colgate & Petschek (1981)

34. Stronger!
Conclusion: The emission frequency, duration and luminosity of an FRB can be well explained .

35. Nature, 505 (2014) 629 a

36. Asteroid belt: 2-4AU; Kuiper belt: 30-60AU; Oort cloud: 5000-10000AU

37. The 1st test ─ clustering bursts
The radius of a pulsar capturing a host star at the center of an asteroid belt is
If the impact radius of this pulsar with the star is less than Rcapture, they will form a self-gravitational binding system.
In such a case, this pulsar could collide with the asteroid belt back and forth, so that many clusters of repeating bursts would be expected to occur. This feature is an observational, unique signature for our model.
Dai et al., arXiv:

38. Scholz et al. 2016, arXiv:

39. The 2nd test ─ duration distribution
SDSS & Subaru Survey
D-2.3
FRBs may provide a probe of extragalactic asteroid belts!
Ivezic et al. 2001; Yoshida et al. 2007
Wang & Yu, arXiv:

40. Chatterjee et al. 2017, Nature, 541, 58
A 100-milliarcsecond localization of FRB by VLA;
A persistent radio source with ~10% flux-density fluctuations;
An optical counterpart with ~25 mag;
Burst clustering: 83-hr observations from 26 April to 20 September 2016, but only 9 bursts in September.

41. Host galaxy of FRB 121102: a low-metallicity, star-forming, mr’=25
Host galaxy of FRB : a low-metallicity, star-forming, mr’=25.1 AB mag dwarf galaxy at a redshift of z = (8), ~1 Gpc.
This host has a diameter~4 kpc, a stellar mass of M*~(4–7)×107Msun, an SFR of ~0.4Msun yr−1, and a substantial host DM≤ 324 pc cm−3.

42. Persistent radio source: ≤0.2mas (~0.7 pc) separation to FRB.
Marcote et al. 2017, ApJ Letters, 834, L8:
Persistent radio source: ≤0.2mas (~0.7 pc) separation to FRB.
Radio-loud AGN, but too far (~0.3” to galactic center);
Supernova ejecta: DMSN  1/t2, but not detected.

43. Non-detection of DM evolution from supernova ejecta
Metzger et al. 2017, arXiv:
Non-detection of DM evolution from supernova ejecta
Piro 2016, ApJL, 824, L32

44. Pulsar wind nebula without supernova ejecta
Ambient medium (zone 1)
Shocked ambient medium (zone 2)
Shocked wind (zone 3)
A relativistic e-e+ wind (zone 4)
Forward shock
Black hole
Termination shock
Contact discontinuity
Dai 2004, ApJ, 606, 1000;
Dai et al. 2017, ApJL, 838, L7

45. The 3rd test?
Within the model frame of Dai et al. (2016)

46. Implications for FRB
Giant pulses from a young magnetar (rotationally-powered, Lyutikov 2017; Cao, Yu & Dai 2017, ApJL, 839, L20): too low spin-down luminosity after a few decades!
Giant flares from a young magnetar (magnetically-powered, Metzger et al. 2017): non-detection of radio emission!
Encounter of a strongly magnetized pulsar with an asteroid belt (gravitationally-powered, Dai et al. 2016)

47. Bagchi 2017, ApJ Letters, 838, L16
The next two times of bursts are expected around 27-Feb-2017 and 18-Dec-2017.

48. Outline Properties of FRBs Some special FRBs Energy source models
Prospects & summary

49. Future observations FAST IS COMING FAST!
Discover its own FRBs;
Find more repeating FRBs;
Deep follow-up to reveal faint radio afterglows of non-repeating FRBs;
Detect GRB- (& GWB-) associated FRBs by joint detections with Swift, SVOM, LIGO, & LOT.
Chinese Large Optical/Infrared
Telescope (LOT)
L. B. Li et al. (2016)

50. From S. Burke-Spolaor (2017)

51. Big FRB Questions
1) What are FRBs? - Neutron stars or AGN or what? - One class or two classes or many? - Emission mechanism? Coherent? - Higher-energy counterparts? 2) Event rate, luminosity function, etc? 3) Cosmological probes?

52. Six eras on gamma-ray bursts
1) “Dark” era ( ): discovery
Klebesadel, Strong & Olson’s discovery (1973);
2) BATSE era ( ): spatial distribution
Meegan & Fishman’s discovery (1992),
detection rate: ~1 to 3 /day, ~3000 bursts;
3) BeppoSAX era ( ): afterglows
van Paradijs, Costa, Frail’s discoveries (1997)
4) HETE-2 era ( ): origin of long bursts
Observations on GRB030329/SN2003dh
5) Swift era (2004-): origin of short bursts, early afterglows
Gehrels, Burrows, Nousek et al. (2005)
6) Fermi era (2008-): high-energy gamma-rays
Since 1992, astronomers have detected GRBs at a rate of 1 to 3 per day. So far about 3000 GRBs have been detected. In the following I briefly review the temporal features, spectral features, spatial features and afterglow features.

53. Summary
FRBs (like GRBs) are not only at cosmological distances but also possibly have two types.
For non-repeating class, associations of GWBs /FRBs/short GRBs (triplets) would be testable in FAST/Swift/SVOM/LIGO era.
For repeating class, impacts of pulsars/asteroid belts would be testable in FAST era.
Counterparts should uncover origins of FRBs!