Unifying Circumstellar Environment in Broad-Lined Type Ic Radio Supernovae Towards Off-axis Gamma-Ray Burst Exploration

TL;DR

The paper develops a unified framework for radio emission from Type Ic-bl SNe hosting off-axis GRB jets by coupling SN shock and GRB afterglow in a wind-like circumstellar medium. It demonstrates that composite light curves can exhibit double peaks under specific energetic and geometric conditions, and applies the model to SN 2007bg to illustrate potential off-axis GRB signatures. Analytic diagnostics and a morphology atlas are provided to predict when double-peaked radio behavior should appear, guiding long-term, multi-band radio monitoring of nearby IcBL SNe. The work offers a pathway to constrain the true GRB incidence among IcBL SNe and to illuminate GRB–SN progenitor physics, with implications for future facilities like the SKA.

Abstract

Decades have passed since the first confirmed association between a broad-lined Type Ic supernova (Type IcBL SN) and a long gamma-ray burst (GRB), and the number of known GRB-SN associations has steadily increased. However, it is important to note that the radiation from GRB afterglows and the radio emission from SNe may be both produced by outflows evolving within the same ambient medium. In this study, we present the first comprehensive theoretical predictions of radio emission from a Type IcBL supernova associated with a GRB jet, explicitly accounting for the structure of the ambient medium. We model each component of the radio emission, with particular emphasis on exploring wide ranges of isotropic explosion energy and viewing angle in our GRB afterglow calculations. We show that, within specific regions of parameter space, the composite radio light curve exhibits a characteristic double-peaked structure. This clear double-peaked feature emerges when either (1) the isotropic explosion energy is small (low-luminosity GRB) or (2) the viewing angle is large (off-axis GRB). Our results demonstrate that follow-up radio observations carried out within a few years of the optical discovery of nearby Type IcBL SNe (-100 Mpc) can provide a unique diagnostic of off-axis GRBs that would otherwise remain undetected in Type IcBL SNe. This represents a step toward revealing the nature of long GRB progenitors and clarifying their connection to Type IcBL SNe.

Figures (5)

• Figure 1: Schematic picture of the system assumed in this study.
• Figure 2: Multi-band radio light curves for SN 2007bg. Each panel corresponds to the different radio frequency. The filled circles are observed data, and open triangles are upper limit. Our demonstrated light curves are shown in dashed (SN), dotted (GRB), and solid (total) lines. The parameters are $E_0=3\times10^{54}$ erg, $A=10\ \rm cm^{-1}$, $p_{\rm GRB}=2.5$, $\epsilon_{e,\rm GRB}=10^{-1}$, $\epsilon_{B,\rm GRB}=10^{-2}$, $\theta_{\rm jet}=0.05$ rad, $\theta_{\rm obs}=1.2$ rad. For SN, $p_{\rm SN}=3.0$, $\epsilon_{e,\rm SN}=3\times10^{-1}$ and $\epsilon_{B,\rm SN}=5\times10^{-2}$.
• Figure 3: Demonstrative superposition of radio light curves (solid) of an SN (dashed) and a GRB afterglow (dotted) for fixed viewing angle $\theta_{\rm obs}=0.8$ rad. From the top to the bottom, the isotropic-equivalent energy is changed as $E_{\rm iso}=10^{50},\ 10^{51},\ 10^{52},\ 10^{53},\ 10^{54},\ 10^{55}$ erg.
• Figure 4: The same as Figure \ref{['fig:demonstration_Eiso']}, but the isotropic-equivalent energy is fixed to $E_{\rm iso}=10^{53}$ erg. From the top to the bottom, the viewing angle is changed as $\theta_{\rm obs}=$ 0.0, 0.2, 0.5, 0.8, 1.2, 1.5 rad.
• Figure 5: The characteristic $(E_{\rm iso},\theta_{\rm obs})$ plane for $A=1$ (left panel) and $A=10$ (right panel). The blue-dotted lines express the typical peak time of the GRB radio afterglow, meanwhile the typical SN peak is around 10 days. The black shaded regions corresponds to 'partial' cases. The fixed parameters are $\Gamma_0=100$, $p_{\rm GRB}=2.5$, $\epsilon_{e,\rm GRB}=10^{-1}$, $\epsilon_{B,\rm GRB}=10^{-2}$, $\theta_{\rm jet}=0.05$ rad. For SN, $p_{\rm SN}=3.0$, $\epsilon_{e,\rm SN}=10^{-1}$ and $\epsilon_{B,\rm SN}=10^{-2}$. The source distance is assumed as $D_{\rm L}=100$ Mpc and $z=0.024$.