Low Radio Frequency Observations and Spectral Modelling of the Remnant of Supernova 1987A

Abstract

We present Murchison Widefield Array observations of the supernova remnant (SNR) 1987A between 72 and 230 MHz, representing the lowest frequency observations of the source to date. This large lever arm in frequency space constrains the properties of the circumstellar medium created by the progenitor of SNR 1987A when it was in its red supergiant phase. As of late-2013, the radio spectrum of SNR 1987A between 72 MHz and 8.64 GHz does not show any deviation from a non-thermal power-law with a spectral index of $-0.74\pm 0.02$. This spectral index is consistent with that derived at higher frequencies, beneath 100 GHz, and with a shock in its adiabatic phase. A spectral turnover due to free-free absorption by the circumstellar medium has to occur below 72 MHz, which places upper limits on the optical depth of $\le$ 0.1 at a reference frequency of 72 MHz, emission measure of $\lesssim$ 13,000 cm${}^{-6}$ pc, and an electron density of $\lesssim$ 110 cm${}^{-3}$. This upper limit on the electron density is consistent with the detection of prompt radio emission and models of the X-ray emission from the supernova. The electron density upper limit implies that some hydrodynamic simulations derived a red supergiant mass loss rate that is too high, or a wind velocity that is too low. The mass loss rate of $\sim 5\times 10^{-6}$ $M_{\odot }$ yr${}^{-1}$ and wind velocity of 10 km s${}^{-1}$ obtained from optical observations are consistent with our upper limits, predicting a current turnover frequency due to free-free absorption between 5 and 60 MHz.

arXiv comment9 pages, accepted by MNRAS

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Cited by in corpus (13)

• Statistical Analysis of Supernova Remnants in the Large Magellanic Cloud
• High angular resolution ALMA images of dust and molecules in the SN 1987A ejecta
• Radio Evolution of Supernova Remnants Including Non-linear Particle Acceleration: Insights from Hydrodynamic Simulations
• The 30-Year Search for the Compact Object in SN 1987A
• Radio Source Extraction with ProFound
• The ASKAP-EMU Early Science Project: 888 MHz Radio Continuum Survey of the Large Magellanic Cloud
• Connecting X-ray absorption and 21cm neutral hydrogen absorption in obscured radio AGN
• Detection of Linear Polarization in the Radio Remnant of Supernova 1987A
• Sensitivity of the Cherenkov Telescope Array to TeV photon emission from the Large Magellanic Cloud
• Radio modelling of the brightest and most luminous non-thermal colliding-wind binary Apep
• Polarized radio emission unveils the structure of the pre-supernova circumstellar magnetic field and the radio emission in SN1987A
• The Radio Remnant of Supernova 1987A - A Broader View
• A Radio Continuum Study of NGC 2082