# Observations of fast radio bursts at frequencies down to 400 megahertz

## Abstract

Fast radio bursts (FRBs) are highly dispersed millisecond-duration radio flashes probably arriving from far outside the Milky Way1,2. This phenomenon was discovered at radio frequencies near 1.4 gigahertz and so far has been observed in one case3 at as high as 8 gigahertz, but not at below 700 megahertz in spite of substantial searches at low frequencies4,5,6,7. Here we report detections of 13 FRBs at radio frequencies as low as 400 megahertz, on the Canadian Hydrogen Intensity Mapping Experiment (CHIME) using the CHIME/FRB instrument8. They were detected during a telescope pre-commissioning phase, when the sensitivity and field of view were not yet at design specifications. Emission in multiple events is seen down to 400 megahertz, the lowest radio frequency to which the telescope is sensitive. The FRBs show various temporal scattering behaviours, with the majority detectably scattered, and some apparently unscattered to within measurement uncertainty even at our lowest frequencies. Of the 13 reported here, one event has the lowest dispersion measure yet reported, implying that it is among the closest yet known, and another has shown multiple repeat bursts, as described in a companion paper9. The overall scattering properties of our sample suggest that FRBs as a class are preferentially located in environments that scatter radio waves more strongly than in the diffuse interstellar medium in the Milky Way.

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## Data availability

The raw data used in this publication are available at https://chime-frb-open-data.github.io/.

## References

1. 1.

Lorimer, D. R., Bailes, M., McLaughlin, M. A., Narkevic, D. J. & Crawford, F. A bright millisecond radio burst of extragalactic origin. Science 318, 777–780 (2007).

2. 2.

Thornton, D. et al. A population of fast radio bursts at cosmological distances. Science 341, 53–56 (2013).

3. 3.

Gajjar, V. et al. Highest frequency detection of FRB 121102 at 4–8 GHz using the breakthrough listen digital backend at the Green Bank Telescope. Astrophys. J. 863, 2 (2018).

4. 4.

Karastergiou, A. et al. Limits on fast radio bursts at 145 MHz with ARTEMIS, a real-time software backend. Mon. Not. R. Astron. Soc. 452, 1254–1262 (2015).

5. 5.

Rowlinson, A. et al. Limits on fast radio bursts and other transient sources at 182 MHz using the Murchison Widefield Array. Mon. Not. R. Astron. Soc. 458, 3506–3522 (2016).

6. 6.

Amiri, M. et al. Limits on the ultra-bright fast radio burst population from the CHIME pathfinder. Astrophys. J. 844, 161 (2017).

7. 7.

Chawla, P. et al. A search for fast radio bursts with the GBNCC pulsar survey. Astrophys. J. 844, 140 (2017).

8. 8.

The CHIME/FRB Collaboration et al. The CHIME fast radio burst project: system overview. Astrophys. J. 863, 48 (2018).

9. 9.

The CHIME/FRB Collaboration. A second source of repeating fast radio bursts. Nature 566, https://doi.org/10.1038/s41586-018-0864-x (2019).

10. 10.

Bandura, K. et al. ICE: A scalable, low-cost FPGA-based telescope signal processing and networking system. J. Astron. Instrum. 05, 1641005 (2016).

11. 11.

Denman, N. et al. A GPU-based correlator X-engine implemented on the CHIME pathfinder. Preprint at http://ArXiv.org/abs/1503.06202 (2015).

12. 12.

Champion, D. J. et al. Five new fast radio bursts from the HTRU high-latitude survey at Parkes: first evidence for two-component bursts. Mon. Not. R. Astron. Soc. 460, L30–L34 (2016).

13. 13.

Sokolowski, M. et al. No low-frequency emission from extremely bright fast radio bursts. Astrophys. J. Lett. 867, L12 (2018).

14. 14.

Macquart, J.-P. & Koay, J. Y. Temporal smearing of transient radio sources by the intergalactic medium. Astrophys. J. 776, 125 (2013).

15. 15.

Zhu, W., Feng, L.-L. & Zhang, F. The scattering of FRBs by the intergalactic medium: variations, strength, and dependence on dispersion measures. Astrophys. J. 865, 147 (2018).

16. 16.

Ravi, V. & Loeb, A. Explaining the statistical properties of fast radio bursts with suppressed low-frequency emission. Preprint at http://ArXiv.org/abs/1811.00109 (2018).

17. 17.

Cordes, J. M. & Lazio, T. J. W. NE2001. I. A new model for the galactic distribution of free electrons and its fluctuations. Preprint at http://ArXiv.org/abs/astro-ph/0207156 (2002).

18. 18.

Yao, J. M., Manchester, R. N. & Wang, N. A new electron-density model for estimation of pulsar and FRB distances. Astrophys. J. 835, 29 (2017).

19. 19.

McQuinn, M. Locating the “missing” baryons with extragalactic dispersion measure estimates. Astrophys. J. 780, L33 (2013).

20. 20.

Dolag, K., Gaensler, B. M., Beck, A. M. & Beck, M. C. Constraints on the distribution and energetics of fast radio bursts using cosmological hydrodynamic simulations. Mon. Not. R. Astron. Soc. 451, 4277–4289 (2015).

21. 21.

Anderson, L. D. et al. The WISE catalog of galactic H II regions. Astrophys. J. Suppl. Ser. 212, 1 (2014).

22. 22.

Avedisova, V. A catalog of star-forming regions in the galaxy. Astron. Rep. 46, 193–205 (2002).

23. 23.

Inoue, S. Probing the cosmic reionization history and local environment of gamma-ray bursts through radio dispersion. Mon. Not. R. Astron. Soc. 348, 999–1008 (2004).

24. 24.

Xu, S. & Zhang, B. On the origin of the scatter broadening of fast radio burst pulses and astrophysical implications. Astrophys. J. 832, 199 (2016).

25. 25.

Cordes, J. M., Wharton, R. S., Spitler, L. G., Chatterjee, S. & Wasserman, I. Radio wave propagation and the provenance of fast radio bursts. Preprint at http://ArXiv.org/abs/1605.05890 (2016).

26. 26.

Farah, W. et al. FRB microstructure revealed by the real-time detection of FRB170827. Mon. Not. R. Astron. Soc. 478, 1209–1217 (2018).

27. 27.

Connor, L., Sievers, J. & Pen, U.-L. Non-cosmological FRBs from young supernova remnant pulsars. Mon. Not. R. Astron. Soc. 458, L19–L23 (2016).

28. 28.

Kumar, P., Lu, W. & Bhattacharya, M. Fast radio burst source properties and curvature radiation model. Mon. Not. R. Astron. Soc. 468, 2726–2739 (2017).

29. 29.

Margalit, B. & Metzger, B. D. A concordance picture of FRB 121102 as a flaring magnetar embedded in a magnetized ion-electron wind nebula. Preprint at http://ArXiv.org/abs/1808.09969 (2018).

30. 30.

Pen, U.-L. & Levin, Y. Pulsar scintillations from corrugated reconnection sheets in the interstellar medium. Mon. Not. R. Astron. Soc. 442, 3338–3346 (2014).

31. 31.

Connor, L. et al. Constraints on the FRB rate at 700–900 MHz. Mon. Not. R. Astron. Soc. 460, 1054–1058 (2016).

32. 32.

Ravi, V. The observed properties of fast radio bursts. Mon. Not. R. Astron. Soc. 482, 1966–1978 (2019).

33. 33.

Ng, C. et al. CHIME FRB: An application of FFT beamforming for a radio telescope. Preprint at http://ArXiv.org/abs/1702.04728 (2017).

34. 34.

Newburgh, L. B. et al. Calibrating CHIME: a new radio interferometer to probe dark energy. Proc. SPIE 9145, 91454V (2014).

35. 35.

Thompson, A. R., Moran, J. M. & Swenson, G. W. Jr Interferometry and Synthesis in Radio Astronomy 3rd edn (Springer, Cham, 2017).

36. 36.

Taylor, J. H. A sensitive method for detecting dispersed radio emission. Astron. Astrophys. Suppl. 15, 367–369 (1974).

37. 37.

Cortes, C. & Vapnik, V. Support-vector networks. Mach. Learn. 20, 273–297 (1995).

38. 38.

Obrocka, M., Stappers, B. & Wilkinson, P. Localising fast radio bursts and other transients using interferometric arrays. Astron. Astrophys. 579, A69 (2015).

39. 39.

Petroff, E. et al. A fast radio burst with a low dispersion measure. Mon. Not. R. Astron. Soc. 482, 3109–3115 (2018).

40. 40.

Lorimer, D. R. & Kramer, M. Handbook of Pulsar Astronomy (Cambridge Univ. Press, Cambridge, 2012).

41. 41.

Goodman, J. & Weare, J. Ensemble samplers with affine invariance. Commun. Appl. Math. Comput. Sci. 5, 65–80 (2010).

42. 42.

Foreman-Mackey, D., Hogg, D. W., Lang, D. & Goodman, J. emcee: The MCMC Hammer. Publ. Astron. Soc. Pacif. 125, 306–312 (2013).

43. 43.

Bhandari, S. et al. The SUrvey for Pulsars and Extragalactic Radio Bursts – II. New FRB discoveries and their follow-up. Mon. Not. R. Astron. Soc. 475, 1427–1446 (2018).

44. 44.

Cordes, J. M. & McLaughlin, M. A. Searches for fast radio transients. Astrophys. J. 596, 1142–1154 (2003).

45. 45.

Ioka, K. The cosmic dispersion measure from gamma-ray burst afterglows: probing the reionization history and the burst environment. Astrophys. J. 598, L79–L82 (2003).

46. 46.

Cordes, J. M. & Lazio, T. J. W. NE2001. II. Using radio propagation data to construct a model for the galactic distribution of free electrons. http://xxx.lanl.gov/abs/astro-ph/0301598 (2003).

47. 47.

Lorimer, D. R. et al. The Parkes Multibeam Pulsar Survey – VI. Discovery and timing of 142 pulsars and a Galactic population analysis. Mon. Not. R. Astron. Soc. 372, 777–800 (2006).

48. 48.

Faucher-Giguère, C.-A. & Kaspi, V. M. Birth and evolution of isolated radio pulsars. Astrophys. J. 643, 332–355 (2006).

49. 49.

Vedantham, H. K. & Phinney, E. S. Radio wave scattering by circumgalactic cool gas clumps. Mon. Not. R. Astron. Soc. 483, 971–984 (2019).

50. 50.

Masui, K. et al. Dense magnetized plasma associated with a fast radio burst. Nature 528, 523–525 (2015).

## Author information

All authors on this paper played either leadership or significant supporting roles in one or more of the following: the management, development and construction of the CHIME telescope, the CHIME/FRB instrument and the CHIME/FRB software data pipeline, the commissioning and operations of the CHIME/FRB instrument, the data analysis and preparation of this manuscript.

Correspondence to S. P. Tendulkar.

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### Competing interests

The authors declare no competing interests.

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Amiri, M., Bandura, K., Bhardwaj, M. et al. Observations of fast radio bursts at frequencies down to 400 megahertz. Nature 566, 230–234 (2019). https://doi.org/10.1038/s41586-018-0867-7

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