Abstract
Abstract We present High Sensitivity Array and enhanced Multi-Element Remotely Linked Interferometer Network observations of the radio-loud broad-lined Type Ic supernova PTF11qcj obtained ∼7.5 yr after the explosion. Previous observations of this supernova at 5.5 yr since explosion showed a double-peaked radio light curve accompanied by a detection in the X-rays, but no evidence for broad Hα spectral features. The Very Long Baseline Interferometry (VLBI) observations presented here show that the PTF11qcj GHz radio ejecta remains marginally resolved at the submilliarcsecond level ≈7.5 yr after the explosion, pointing toward a nonrelativistic expansion. Our VLBI observations thus favor a scenario in which the second peak of the PTF11qcj radio light curve is related to the strong interaction of the supernova ejecta with a circumstellar medium of variable density, rather than to the emergence of an off-axis jet. Continued VLBI monitoring of PTF11qcj in the radio may further strengthen this conclusion.
Highlights
Supernovae (SNe) of Type Ib/c are believed to mark the deaths of massive stars that are stripped of their hydrogen (Type Ib), and possibly helium (Type Ic), envelope before explosion (Filippenko 1997)
Because nonthermal radio photons are produced in the interaction of the SN shock with the circumstellar material (CSM), bright radio emission can be the smoking gun for ejecta interacting with a high-density CSM (e.g., Chevalier 1998; Chevalier et al 2004; Chevalier & Fransson 2006)
We have presented High Sensitivity Array (HSA) and Element Remotely Linked Interferometer Network (eMERLIN) observations of PTF11qcj obtained ∼7.5 yr postexplosion
Summary
Supernovae (SNe) of Type Ib/c are believed to mark the deaths of massive stars that are stripped of their hydrogen (Type Ib), and possibly helium (Type Ic), envelope before explosion (Filippenko 1997). As discussed in Palliyaguru et al (2019), two more complex scenarios can be invoked to interpret this peculiar behavior of PTF11qcj: (i) a spherical SN shock going through a medium with extreme CSM density variations, perhaps related to eruptive progenitor mass loss, and (ii) a radio-emitting SN shock (first peak) followed by radio emission from an emerging off-axis GRB jet, initially pointed away from our line of sight (second peak). Here we present Very Long Baseline Interferometry (VLBI) observations of PTF11qcj aimed at setting direct constraints on the size (angular diameter) of its radio ejecta These observations provide a direct test for the presence of relativistic expansion, as expected in the case of an off-axis GRB jet.
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