{
  "id": "1903.05505",
  "version": "v1",
  "published": "2019-03-13T14:17:40.000Z",
  "updated": "2019-03-13T14:17:40.000Z",
  "title": "Thermal emission from bow shocks I: 2D Hydrodynamic Models of the Bubble Nebula",
  "authors": [
    "Samuel Green",
    "Jonathan Mackey",
    "Thomas J. Haworth",
    "Vasilii V. Gvaramadze",
    "Peter Duffy"
  ],
  "comment": "Accepted for publication in Astronomy & Astrophysics",
  "categories": [
    "astro-ph.GA"
  ],
  "abstract": "The Bubble Nebula (or NGC 7635) is a parsec-scale seemingly spherical wind-blown bubble around the relatively unevolved O star BD+60$^\\circ$2522. The small dynamical age of the nebula and significant space velocity of the star suggest that the Bubble Nebula might be a bow shock. We have run 2D hydrodynamic simulations to model the interaction of the central star's wind with the interstellar medium (ISM). The models cover a range of possible ISM number densities of $n=50-200 {\\rm cm}^{-3}$ and stellar velocities of $v_{\\star}=20-40$ km s$^{-1}$. Synthetic H$\\alpha$ and 24 $\\mu$m emission maps predict the same apparent spherical bubble shape with quantitative properties similar to observations. The synthetic maps also predict a maximum brightness similar to that from the observations and agree that the maximum brightness is at the apex of the bow shock. The best-matching simulation had $v_{\\star}\\approx20$ km s$^{-1}$ into an ISM with $n\\sim100 {\\rm cm}^{-3}$, at an angle of 60$^\\circ$ with respect to the line of sight. Synthetic maps of soft ($0.3-2$ keV) and hard ($2-10$ keV) X-ray emission show that the brightest region is in the wake behind the star and not at the bow shock itself. The unabsorbed soft X-rays have luminosity $\\sim10^{32}-10^{33}$ erg s$^{-1}$. The hard X-rays are fainter, luminosity $\\sim 10^{30} - 10^{31}$ erg s$^{-1}$, and may be too faint for current X-ray instruments to successfully observe. Our results imply that the O star creates a bow shock as it moves through the ISM and in turn creates an asymmetric bubble visible at optical and infrared wavelengths, and predicted to be visible in X-rays. The Bubble Nebula does not appear to be unique, it could be just a favourably oriented very dense bow shock. The dense ISM surrounding BD+60$^\\circ$2522 and its strong wind suggest that it could be a good candidate for detecting non-thermal emission.",
  "revisions": [
    {
      "version": "v1",
      "updated": "2019-03-13T14:17:40.000Z"
    }
  ],
  "analyses": {
    "keywords": [
      "bow shock",
      "bubble nebula",
      "2d hydrodynamic models",
      "thermal emission",
      "seemingly spherical wind-blown bubble"
    ],
    "note": {
      "typesetting": "TeX",
      "pages": 0,
      "language": "en",
      "license": "arXiv",
      "status": "editable"
    }
  }
}