[Steely Tom]

One article pertaining to this phenomenon states that the radiation is both "coherent" and "relatively broadband." I'm having a hard time picturing how radiation can have these two characteristics simultaneously unless it is a modulated carrier.

Also, the above-referenced article states that the bursts have a wavelength of about 1 meter (300 MHz) and have been observed to repeat at intervals of 77 minutes.

[Lonesome in Massachussets]

One article pertaining to this phenomenon states that the radiation is both "coherent" and "relatively broadband." I'm having a hard time picturing how radiation can have these two characteristics simultaneously unless it is a modulated carrier.

Doesn't seem to be the same phenomenon. The article is dated prior to the discovery of the sources in the Time article and refers to sources in the center of the Milky Way, not extra galactic sources.

The article did not say that the sources were "broadband", but occurred over a very large bandwidth. I take that to mean that any single source is coherent, i.e., narrowband, but the population includes sources at various wavelengths. (For objects within the Milky Was, it is unlikely that Doppler shift could cause very large Doppler shifts.)