The Presupernova H II Region around SN 1987A

摘要: The slow expansion of the bright ring around SN 1987A and large size estimated for radio source at an age ~1500 days suggest a low mass-loss rate, , from blue supergiant progenitor star; we adopt = 7.5 × 10-8 M☉ yr-1 wind velocity vw 450 km s-1 as standard values. This density would not give substantial free-free absorption during first few when low-frequency was observed, but turnover can be attributed to synchrotron self-absorption. X-ray emission observed since 1990 require that supernova shock interacting with denser gas than in free wind. We propose it is H II region created by B3 Ia star swept-up red extends radius rII ≈ 3 1017 cm R 6 equatorial plane has hydrogen ~102 cm-3. front will reach dense until year 2005 ± 3. luminosity should slowly increase time. ionization trapped gas; its associated bipolar nebula are initially neutral part shell. In polar direction, broke out gas, there no shell, consistent lack thin shell direction.