{
  "id": "1903.04498",
  "version": "v1",
  "published": "2019-03-11T18:00:02.000Z",
  "updated": "2019-03-11T18:00:02.000Z",
  "title": "Multi-wavelength spectroscopy of the black hole candidate MAXI J1813-095 during its discovery outburst",
  "authors": [
    "M. Armas Padilla",
    "T. Muñoz-Darias",
    "J. Sánchez-Sierras",
    "B. De Marco",
    "F. Jiménez-Ibarra",
    "J. Casares",
    "J. M. Corral-Santana",
    "M. A. P. Torres"
  ],
  "comment": "9 pages, 6 figures, 2 tables. Accepted for publication in MNRAS",
  "categories": [
    "astro-ph.HE",
    "hep-ph"
  ],
  "abstract": "MAXI J1813-095 is an X-ray transient discovered during an outburst in 2018. We report on X-ray and optical observations obtained during this event, which indicate that the source is a new low-mass X-ray binary. The outburst lasted ~70 d and peaked at Lx(0.5-10keV)~7.6 x 10^36 erg s-1, assuming a distance of 8 kpc. Swift/XRT follow-up covering the whole activity period shows that the X-ray emission was always dominated by a hard power-law component with a photon index in the range of 1.4-1.7. These values are consistent with MAXI J1813-095 being in the hard state, in agreement with the ~30 per cent fractional root-mean-square amplitude of the fast variability (0.1-50 Hz) inferred from the only XMM-Newton observation available. The X-ray spectra are well described by a Comptonization emission component plus a soft, thermal component (kT ~0.2 keV), which barely contributes to the total flux (<8 per cent). The Comptonization y-parameter (~1.5), together with the low temperature and small contribution of the soft component supports a black hole accretor. We also performed optical spectroscopy using the VLT and GTC telescopes during outburst and quiescence, respectively. In both cases the spectrum lack emission lines typical of X-ray binaries in outburst. Instead, we detect the Ca II triplet and H_alpha in absorption. The absence of velocity shifts between the two epochs, as well as the evolution of the H_alpha equivalent width, strongly suggest that the optical emission is dominated by an interloper, likely a G-K star. This favours a distance >3 kpc for the X-ray transient.",
  "revisions": [
    {
      "version": "v1",
      "updated": "2019-03-11T18:00:02.000Z"
    }
  ],
  "analyses": {
    "keywords": [
      "black hole candidate maxi",
      "discovery outburst",
      "multi-wavelength spectroscopy",
      "x-ray transient",
      "comptonization emission component plus"
    ],
    "note": {
      "typesetting": "TeX",
      "pages": 9,
      "language": "en",
      "license": "arXiv",
      "status": "editable"
    }
  }
}