Fast radio bursts

Fast radio burst (FRBs)

Fast radio bursts (FRBs) are millisecond-duration radio pulses with a peak frequency at around 1.4 GHz. Some FRBs show repeating pulses while some are not. They are suggested to be extragalactic sources, with some of them might originate from magnetars. In some respects they are similar to radio pulses from pulsars and magnetars, but with a much higher flux density. The high brightness temperature suggests their radiation must be coherent, yet the radiation mechanism is unclear. Some FRBs are associated with electromagnetic couterparts, making them perfect candidates to study their central engine and radiation mechanisms.

Observations indicate that nearby FRBs can be produced by both young stellar populations, as suggested by the detection of FRB 20200428 from a Galactic magnetar SGR 1935+2154, and old stellar populations, as suggested by the localization of the repeating source FRB 20200120E in a globular cluster of M81. Howerver, the burst energies of FRB 20200120E are significantly smaller than those of other cosmological FRBs, even falling below the energy of the Galactic event FRB 20200428. Additionally, its burst energy distribution displays a steep power law tail at high fluences. It is unclear whether this type of source can contribute to the cosmological FRB population. Recently, we have detected a burst from FRB 20200120E in 1.1-1.7 GHz, with a fluence of approximately 31.4 Jy ms, which is more than 44 times larger than the previous detected bursts 1.4 GHz frequencies and five times more energetic than FRB 20200428. It reaches one-third of the energy of the weakest burst from FRB 20121102A detected so far and is detectable at a distance exceeding 200Mpc. This suggests that globular clusters can host cosmological FRBs, and the currently localized FRB sample could contain FRBs from globular clusters. Together with SGR 1935+2154, these two most nearby sources support multiple progenitor sources for FRBs.

Ref:Zhang, Wang and Yang et al., 2023, arXiv:2310.00908 https://ui.adsabs.harvard.edu/abs/2023arXiv231000908Z/abstract

FRB radiation mechanism

Recently, a fast radio burst (FRB)-like event was found to be associated with a Galactic magnetar, SGR 1935+2154, accompanied by an X-ray burst. We find this radio burst challenges the typical emission mechanisms involving magnetars, especially for the coherent curvature radiation from charged bunches, and synchrotron maser from shocks.

We then revisit the intermediate-field FRB model where the radio waves are generated as fast-magnetosonic waves through magnetic reconnection near the light cylinder (see the figure on the right). The current sheet in the magnetar wind is compressed by a low frequency pulse emitted from the inner magnetosphere to trigger magnetic reconnection. We find that this model can naturally and self-consistently interpret the X-ray/radio event from SGR 1935+2154 and the QPO in FRB 20191221A. It can also explain the observed wide energy range of repeating FRBs in a narrow bandwidth.

Ref: Wang, 2020, ApJ, https://iopscience.iop.org/article/10.3847/1538-4357/aba955

Wang et al. 2023, RAA, 23, 035010 https://ui.adsabs.harvard.edu/abs/2023RAA....23c5010W/abstract

FRB models and EM counterparts

FRBs can have electromagnetic counterparts, as such activity usually are associated with outflows. For repeating FRB, a nebula might be produced by the electron synchrotron radiaiton in the outflow. We find this nebula can explain very well of the persistent radio counterpart of FRB 121102 (see the right figure), but requires an average energy injection rate into the nebula to be between 10^39 erg/s and 10^44 erg/s. Consequently, for FRB 121102 and its nebula: (1) WD and accretion BH central engines are disfavored; (2) a rotation- powered NS central engine works when 10^12 G < B < 7.8 *10^14 G with initial period P < 180 ms, but the radio emission must be more efficient than that in typical giant pulses of radio pulsars; and (3) a magnetic- powered NS central engine works when its internal magnetic field B_*>10^16 G. We also find that the radio-emitting electrons in the nebula could produce a significant rotation measure (RM), but cannot account for the entire observed RM of FRB 121102.

Ref: Wang & Lai 2020, ApJ, https://iopscience.iop.org/article/10.3847/1538-4357/aba955

Non-repeating FRBs could possiblty produced by the magnetospheric interaction during the neutron star inspirals (see the right figure), if the radio radiation is coherent. In this framework, we propose the repeating FRBs are produced between the collisions of asteroids and magnetised neutron stars. In this X/gamma-ray bursts and gravitational wave radiation might be associated with FRBs.

Ref: Wang et al. 2016, ApJL, https://iopscience.iop.org/article/10.3847/2041-8205/822/1/L7

Dai, Wang, Wu, & Huang, 2016, ApJL, https://iopscience.iop.org/article/10.3847/0004-637X/829/1/27

Page updated

Google Sites

Report abuse