2018ApJ...856...56C

The energy source powering the extreme optical luminosity of hydrogen-stripped superluminous supernovae (SLSNe-I) is not known, but recent studies have highlighted the case for a central engine. Radio and/or X-ray observations are best placed to track the fastest ejecta and probe the presence of outflows from a central engine. We compile all the published radio observations of SLSNe-I to date and present three new observations of two new SLSNe-I. None were detected. Through modeling the radio emission, we constrain the subparsec environments and possible outflows in SLSNe-I. In this sample, we rule out on-axis collimated relativistic jets of the kind detected in gamma-ray bursts (GRBs). We constrain off-axis jets with opening angles of 5° (30°) to energies of E_k< 4×10⁵⁰erg (E_k< 10⁵⁰erg) in environments shaped by progenitors with mass-loss rates of {dot}M< 10^–4M_☉yr^–1 ({dot}M< 10^–5M_☉yr^–1) for all off-axis angles, assuming fiducial values ε_e=0.1 and ε_B=0.01. The deepest limits rule out emission of the kind seen in faint uncollimated GRBs (with the exception of GRB 060218) and from relativistic SNe. Finally, for the closest SLSN-I, SN 2017egm, we constrain the energy of an uncollimated nonrelativistic outflow like those observed in normal SNe to E_k≲10⁴⁸ erg.