2025ApJ...995...61S

Hydrogen/helium-poor stripped-envelope core-collapse supernovae with broad lines (SNe Ic-bl) almost always accompany the nearby (z < 0.3) jetted relativistic explosions known as long duration gamma-ray bursts (GRBs). However, the majority of SNe Ic-bl have no detected GRB counterpart. At least some of these SNe should harbor off-axis jets, whose afterglow may become detectable at late times, particularly at radio wavelengths. Here, we present Karl G. Jansky Very Large Array (VLA) radio observations (rest-frame times of ∼3-4 × 10³ days post SN discovery) of a sample of 14 SNe Ic-bl discovered by the Palomar Transient Factory (PTF) that have been demonstrated to originate from the same host environments as the SNe Ic-bl associated with nearby GRBs. Of the 14 SNe, we identify three that are radio detected, one of which (PTF10tqv, z = 0.0795) is consistent with an off-axis jet with energy similar to classical GRBs (∼10⁵¹-10^51.7 erg). Using recently developed synchrotron radiation code, we find that for our 11 nondetections, which are among the deepest limits obtained for Ic-bl, we rule out an off-axis jet with an energy of ≳10⁵¹ erg in circumburst densities of ≳10^–1 cm^–3. We predict that well-spaced monitoring of newly discovered SNe Ic-bl from ∼10 days to ∼10 yr (rest frame) to luminosities of ∼10²⁷ erg s^–1 Hz^–1 will constrain the existence of highly off-axis jets (≳60°) with classical GRB energies. The VLA Sky Survey will probe jets that are ≲60° off-axis, whereas the Deep Synpotic Array 2000 will probe jets out to ∼90° off-axis, demonstrating the importance of utilizing radio surveys to supplement targeted observations.