2009/02/06 by A. Tziamtzis, M. Schirmer, P. Lundqvist +1 · 14 citations
Physics and Astronomy · #Astronomy and Astrophysical Research #Astrophysics and Cosmic Phenomena #Brightness #Crab Nebula #Gamma-ray bursts and supernovae #Halo #Kinetic energy #Scattering #Spectral line #Supernova #Surface brightness #astro-ph.SR
paper · pdf · doi:10.1051/0004-6361/200811385
published in Astronomy and Astrophysics 497(1), 167-176 (EDP Sciences) · 10 pages, 13 figures, accepted for publication in A&A
arxiv created 2009/02/06 · openalex publication_date 2009/02/18 · arxiv updated 2009/12/01 · openalex created_date 2016/06/24 · openalex updated_date 2026/08/05
<i>Aims. <i/>We searched for a fast moving H<i>α<i/> shell around the Crab nebula. Such a shell could account for this supernova remnant's missing mass, and carry enough kinetic energy to make SN 1054 a normal type II event.<i>Methods. <i/>Deep H<i>α<i/> images were obtained with WFI at the 2.2 m MPG/ESO telescope and with MOSCA at the 2.56 m NOT. The data are compared with theoretical expectations derived from shell models with ballistic gas motion, constant temperature, constant degree of ionisation, and a power law for the density profile.<i>Results. <i/>We reach a surface brightness limit of 5 10<sup>-8<sup/> erg s<sup>-1<sup/> cm<sup>-2<sup/> sr<sup>-1<sup/>. A halo is detected, but at a much higher surface brightness than our models of recombination emission and dust scattering predict. Only collisional excitation of Ly<i>β<i/> with partial de-excitation to H<i>α<i/> could explain such amplitudes. We show that the halo seen is caused by PSF scattering and thus not related to a real shell. We also investigated the feasibility of a spectroscopic detection of high-velocity H<i>α<i/> gas towards the centre of the Crab nebula. Modelling the emission spectra shows that such gas easily evades detection in the complex spectral environment of the H<i>α<i/>-line.<i>Conclusions. <i/>PSF scattering significantly contaminates our data, preventing a detection of the predicted fast shell. A real halo with observed peak flux of about 2 10<sup>-7<sup/> erg s<sup>-1<sup/> cm<sup>-2<sup/> sr<sup>-1<sup/> could still be accomodated within our error bars, but our models predict a factor 4 lower surface brightness. Eight meters class telescopes could detect such fluxes unambiguously, provided that a sufficiently accurate PSF model is available. Finally, we note that PSF scattering also affects other research areas where faint haloes are searched for around bright and extended targets.