Abstract
Long-slit spectroscopic CCD observations of the H II region N44C (refs 1–3) in the Large Magellanic Cloud and its central hot, massive star2,3 show that the stellar temperature is far too low to account for the high excitation of the nebula. In particular the strong nebular HeII 4686-Å recombination radiation, which is absent in normal H II regions, cannot be understood in terms of ionization by the stellar ultraviolet flux. Here we propose an alternative interpretation in terms of a (fossil) X-ray photo-ionized nebula resembling the recently discovered He III region around the luminous X-ray binary LMC X-l (ref. 4). In this picture the presently extinct X-ray source that has been responsible for the high ionization in N44C could well be identical with the transient LMC X-5 (refs 5, 6). From photon-counting arguments and re-combination timescales of the interstellar plasma we find that less than 100 years ago the X-ray luminosity should have been compar-able with that of the most luminous X-ray binaries (a few x l038erg s−1). This hypothesis can be tested by future observa-tions.
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Pakull, M., Motch, C. Is N44C a fossil X-ray ionized nebula?. Nature 337, 337–339 (1989). https://doi.org/10.1038/337337a0
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DOI: https://doi.org/10.1038/337337a0
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