The Radio Scream from Black Holes at Cosmic Dawn: A Semi-Analytic Model
  for the Impact of Radio Loud Black-Holes on the 21 cm Global Signal
  We use a semi-analytic model to explore the potential impact of a brief and
violent period of radio-loud accretion onto black-holes (The Radio Scream)
during the Cosmic Dawn on the HI hyperfine 21 cm signal. We find that radio
emission from super-massive black hole seeds can impact the global 21 cm signal
at the level of tens to hundreds of percent provided that they were as radio
loud as $z\approx1$ black holes and obscured by gas with column depths of
$N_\text{H}\gtrsim 10^{23}$ cm$^{-2}$. We determine plausible sets of
parameters that reproduce some of the striking features of the EDGES absorption
feature including its depth, timing, and side steepness while producing
radio/X-ray backgrounds and source counts that are consistent with published
limits. Scenarios yielding a dramatic 21 cm signature also predict large
populations of $\sim \mu$Jy point sources that will be detectable in future
deep surveys from the Square Kilometer Array (SKA). Thus, 21 cm measurements,
complemented by deep point source surveys, have the potential to constrain
optimistic scenarios where super-massive black-hole progenitors were
radio-loud.
