AT2018cow: a luminous millimeter transient

Understand

We present detailed submillimeter- through centimeter-wave observations of the extraordinary extragalactic transient AT2018cow.

• The apparent characteristics -- the high radio luminosity, the long-lived emission plateau at millimeter bands, and the sub-relativistic velocity -- have no precedent.
• A basic interpretation of the data suggests $E_k \gtrsim 10^{48}$ erg coupled to a fast but sub-relativistic ($v \approx 0.13c$) shock in a dense ($n_e \approx 3 \times 10^{5}\,$cm$^{-3}$) medium.
• We find that the X-ray emission is not naturally explained by an extension of the radio-submm synchrotron spectrum, nor by inverse Compton scattering of the dominant blackbody UVOIR photons by energetic electrons within the forward shock.