SN 1998bw

SN 1998bw
Name	SN 1998bw
Type	Ic-BL / hypernova
Discovery date	1998-04-25
Ra	19:35:03.3
Dec	−52:50:44
Host	ESO 184-G82
Distance	~37 Mpc
Constellation	Indus

SN 1998bw was a bright, broad-lined Type Ic supernova discovered in 1998 that became notable for its extreme luminosity, unusually high expansion velocities, and temporal and spatial coincidence with a gamma-ray burst. The event occurred in the spiral galaxy ESO 184-G82 and was rapidly targeted by observers at facilities associated with the European Southern Observatory, the Cerro Tololo Inter-American Observatory, and the Anglo-Australian Telescope. Its properties established connections between core-collapse supernovae, relativistic outflows, and high-energy transients studied by missions such as the Compton Gamma Ray Observatory.

Discovery and observational history

The transient was first reported by the international team operating the International Astronomical Union circulars, with follow-up imaging and spectroscopy carried out by groups at the European Southern Observatory, the National Optical Astronomy Observatory, and the Australian National University. Early photometry used instruments at the Cerro Tololo Inter-American Observatory and the Anglo-Australian Telescope while spectroscopic time series were secured with the Very Large Telescope and the Keck Observatory teams. Rapid coordination involved astronomers associated with the International Astronomical Union, the Harvard-Smithsonian Center for Astrophysics, and the Max Planck Institute for Astronomy, enabling comparison with archival targets from the Hubble Space Telescope and X-ray observations from the Rossi X-ray Timing Explorer and the BeppoSAX mission.

Classification and progenitor system

Spectroscopy obtained by research groups at the European Southern Observatory and the Carnegie Institution showed broad absorption features consistent with stripped-envelope supernovae previously studied by teams at Princeton University and the University of Tokyo. The spectra lacked hydrogen and helium lines noted in other supernova classes cataloged by the Harvard-Smithsonian Center for Astrophysics, leading to a Type Ic designation with exceptionally broad lines (Ic-BL) that echoed properties reported in the literature from the Max Planck Society and the Smithsonian Astrophysical Observatory. Stellar evolution models developed by researchers at the University of California, Santa Cruz and the Monash University group favored a massive Wolf–Rayet progenitor or a massive star in a close binary system as proposed by theorists at the Kavli Institute and the Institute for Advanced Study.

Light curve and spectral evolution

Photometric monitoring by groups affiliated with the European Southern Observatory, the Cerro Tololo Inter-American Observatory, and the Australian National University produced a rapidly rising and luminous light curve that exceeded typical Type Ic templates used by the Supernova Cosmology Project and the Carnegie Supernova Project. Spectral time series from the Keck Observatory, the Very Large Telescope, and the Anglo-Australian Telescope showed extreme Doppler broadening with velocities inferred by teams from the Max Planck Institute and the Harvard-Smithsonian Center for Astrophysics. Comparison to bolometric models published by researchers at the California Institute of Technology and the University of Tokyo implied a large synthesized mass of radioactive nickel, consistent with explosion models advanced at the Kavli Institute for Theoretical Physics and the Barcelona Supernova group.

Association with GRB 980425

The temporal and spatial coincidence with GRB 980425, detected by the BeppoSAX satellite and monitored by the Compton Gamma Ray Observatory team, linked the optical transient to high-energy phenomena studied by the European Space Agency and the NASA Goddard Space Flight Center. The association was examined by investigators at the Massachusetts Institute of Technology, the University of California, Berkeley, and the Space Telescope Science Institute, prompting comparative studies with cosmological gamma-ray bursts cataloged by the Burst and Transient Source Experiment and the Swift mission. Debates between groups at Princeton University, the Max Planck Institute for Extraterrestrial Physics, and the University of Leicester considered whether the event represented an off-axis jet, a low-luminosity class of burst, or a new channel connecting collapsars as formulated by theorists at the Institute for Advanced Study and the Jet Propulsion Laboratory.

Explosion mechanism and energetics

Hydrodynamic and radiative-transfer modeling by teams at the California Institute of Technology, the Max Planck Institute, and the University of Tokyo favored a highly energetic core-collapse explosion often termed a "hypernova" in the literature produced by the Kavli Institute and the Institute of Astronomy, Cambridge. Estimates of kinetic energy derived by researchers at the Harvard-Smithsonian Center for Astrophysics and the University of California, Santa Cruz reached values substantially above canonical supernova energies, consistent with central-engine models invoking a rapidly rotating compact object as proposed by groups at the Institute for Advanced Study and the National Astronomical Observatory of Japan. Alternative simulations from the University of Oxford and the Barcelona Supernova group explored asymmetric explosions, jet-driven outflows, and magnetorotational mechanisms discussed in reviews from the Royal Astronomical Society and the American Astronomical Society.

Remnant and host galaxy environment

The host, the barred spiral galaxy ESO 184-G82 in the constellation Indus, was characterized by observers from the European Southern Observatory, the Australian National University, and the Hubble Space Telescope team as a star-forming galaxy with regions of active massive-star formation similar to systems cataloged by the Sloan Digital Sky Survey and the Two Micron All Sky Survey. Follow-up radio and X-ray campaigns by groups at the National Radio Astronomy Observatory, the Chandra X-ray Center, and the Very Large Array searched for late-time emission and compact remnants analogous to pulsars and black holes studied by the Max Planck Institute for Radio Astronomy and the Jet Propulsion Laboratory. Continued study by the Space Telescope Science Institute and the University of Cambridge aims to constrain the nature of any compact object and the impact of the explosion on the interstellar medium, building on comparative surveys by the Anglo-Australian Observatory and the European Southern Observatory.

Category:Supernovae Category:Type Ic supernovae Category:1998 in astronomy