I’ve read that Fast Radio Bursts are very “intense”, but how is intensity measured?


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Radio astronomers typically characterize the strength of a signal by its flux density, $S_{\nu}$, the power delivered per square meter per unit frequency. The units of flux density are Janskys, with the conversion $$1\;\text{Jansky}=10\times10^{-26}\;\text{Watts}\times\text{meter}^{-2}\times\text{Hertz}^{-1}$$ To find the total flux, then, you simply integrate the flux density across your observing band.

For some numbers: The first detected FRB, discovered in archival 1.4 GHz data and designated FRB 010724 (Lorimer et al. 2007), had a peak flux of roughly 30 Jy during its 5-millisecond duration. Most FRBs fall in the 50 mJy - 100 Jy range - FRB 010724, the Lorimer burst, turned out to be one of the brighter ones. I believe FRB 150807 holds the current record, and around 120 Jy (Ravi et al. 2016), again centered around 1.4 GHz. Then again, the field's progressing fairly steadily, so that could be eclipsed in the near future.

Many FRBs are, as you mentioned, rather intense compared to typical radio sources; it's not too unusual to work with sources on the order of milliJanskys or tens of milliJanskys, depending on the source.

  • $\begingroup$ Do you think you could do a worldbuilding-style comparison to a rock concert? I'm coming up with values on the order of ~100 Jy, but I'm having trouble accounting for bandwidth in that. Rock concerts tend to be around 1W/m^2, but the bandwidth of music is complicated, especially since their power tends to be concentated on low frequencies! $\endgroup$
    – Cort Ammon
    Jun 29, 2020 at 0:43
  • $\begingroup$ @CortAmmon It's an interesting thought, though I wonder how valid that comparison would be, given that we'd be talking about the bandwidth of sound as opposed to the bandwidth of electromagnetic radiation. Given that human hearing spans . . . I think four orders of magnitude of frequency, I get ridiculously high flux density ($\sim10^{21}\;\text{Jy}$) if I use that as a bandwidth. $\endgroup$
    – HDE 226868
    Jun 29, 2020 at 0:58
  • $\begingroup$ the bandwidth is 20 kHz or less. $\endgroup$
    – JEB
    Jun 29, 2020 at 1:36
  • $\begingroup$ but the power spectrum is contoured to accommodate the frequency response of the human ear. this is why bass players like me have to haul around such huge amp stacks. $\endgroup$ Jun 29, 2020 at 1:58

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