A relativistic type Ibc supernova without a detected gamma-ray burst

Area of Science:

• Astrophysics
• Cosmic explosions
• Supernovae and Gamma-Ray Bursts

Background:

• Long-duration gamma-ray bursts (GRBs) are linked to the explosive deaths of massive stars, forming a rare subclass of Type Ibc supernovae.
• These events feature a relativistic outflow from a central engine (black hole or neutron star), observed as gamma-ray pulses and radio afterglows.
• Many GRBs may go undetected due to instrument sensitivity limits or emission beaming away from Earth.

Purpose of the Study:

• To investigate the possibility of detecting previously undiscovered GRBs through radio searches for supernovae with relativistic outflows.
• To identify supernovae exhibiting characteristics of central-engine activity beyond gamma-ray detection.

Main Methods:

• Radio surveys of Type Ibc supernovae were conducted.
• Analysis of luminous radio emission from SN 2009bb to infer the presence of a relativistic outflow.
• Comparison of findings with existing data on GRB rates and supernova populations.

Main Results:

• Luminous radio emission was detected from the Type Ibc supernova SN 2009bb, indicating a substantial relativistic outflow powered by a central engine.
• The study estimates that approximately one percent of Type Ibc supernovae harbor central engines, consistent with independent GRB rate estimates.
• A second, mildly relativistic supernova was also identified independently.

Conclusions:

• Radio observations can reveal hidden gamma-ray burst (GRB) populations by detecting relativistic outflows in supernovae.
• Supernova SN 2009bb provides evidence for central-engine activity in a previously unclassified event.
• The prevalence of central engines in supernovae is low but consistent with observed GRB rates, suggesting a significant population of undetected GRBs.