{
  "id": "2411.19382",
  "version": "v1",
  "published": "2024-11-28T21:22:17.000Z",
  "updated": "2024-11-28T21:22:17.000Z",
  "title": "Can the central compact object in HESS J1731--347 be indeed the lightest neutron star observed?",
  "authors": [
    "Shu-Rui Zhang",
    "Jorge A. Rueda",
    "Rodrigo Negreiros"
  ],
  "comment": "Accepted for publication in ApJ, comments are welcome!",
  "categories": [
    "astro-ph.HE",
    "astro-ph.SR"
  ],
  "abstract": "The exceptionally low mass of $0.77_{-0.17}^{+0.2} M_{\\odot}$ for the central compact object (CCO) XMMU J173203.3 -- 344518 (XMMU J1732) in the supernova remnant (SNR) HESS J1731 -- 347 challenges standard neutron star (NS) formation models. The nearby post-AGB star IRAS 17287 -- 3443 ($\\approx 0.6 M_\\odot$), also within the SNR, enriches the scenario. To address this puzzle, we advance the possibility that the gravitational collapse of a rotating pre-SN iron core ($\\approx 1.2 M_\\odot$) could result in a low-mass NS. We show that angular momentum conservation during the collapse of an iron core rotating at $\\approx 45\\%$ of the Keplerian limit results in a mass loss of $\\approx 0.3 M_\\odot$, producing a stable newborn NS of $\\approx 0.9 M_\\odot$. Considering the possible spin-down, this indicates that the NS is now slowly rotating, thus fulfilling the observed mass-radius relation. Additionally, the NS's surface temperature ($\\approx 2 \\times 10^6$ K) aligns with canonical thermal evolution for its $\\approx 4.5$ kyr age. We propose the pre -- SN star, likely an ultra-stripped core of $\\approx 4.2 M_\\odot$, formed a tidally locked binary with IRAS 17287 -- 3443, having a 1.43-day orbital period. The supernova led to a $\\approx 3 M_\\odot$ mass loss, imparting a kick velocity $\\lesssim 670$ km s$^{-1}$, which disrupted the binary. This scenario explains the observed 0.3 pc offset between XMMU J1732 and IRAS 17287 -- 3443 and supports the possibility of CCOs forming in binaries, with rotation playing a key role in core-collapse, and the CCO XMMU J1732 being the lightest NS ever observed.",
  "revisions": [
    {
      "version": "v1",
      "updated": "2024-11-28T21:22:17.000Z"
    }
  ],
  "analyses": {
    "keywords": [
      "central compact object",
      "lightest neutron star",
      "nearby post-agb star iras",
      "mass loss",
      "challenges standard neutron star"
    ],
    "note": {
      "typesetting": "TeX",
      "pages": 0,
      "language": "en",
      "license": "arXiv",
      "status": "editable"
    }
  }
}