{
  "id": "1311.1519",
  "version": "v1",
  "published": "2013-11-06T21:00:30.000Z",
  "updated": "2013-11-06T21:00:30.000Z",
  "title": "Optical and X-ray emission from stable millisecond magnetars formed from the merger of binary neutron stars",
  "authors": [
    "Brian D. Metzger",
    "Anthony L. Piro"
  ],
  "comment": "13 pages, 8 figures, 2 appendices, submitted to MNRAS",
  "categories": [
    "astro-ph.HE"
  ],
  "abstract": "The coalescence of binary neutron stars (NSs) may in some cases produce a stable massive NS remnant rather than a black hole. Due to the substantial angular momentum from the binary, such a remnant is born rapidly rotating and likely acquires a strong magnetic field (a `millisecond magnetar'). Magnetic spin-down deposits a large fraction of the rotational energy from the magnetar behind the small quantity of mass ejected during the merger. This has the potential for creating a bright transient that could be useful for determining whether a NS or black hole was formed in the merger. We investigate the expected signature of such an event, including for the first time the important impact of electron/positron pairs injected by the millisecond magnetar into the surrounding nebula. These pairs cool via synchrotron and inverse Compton emission, producing a pair cascade and hard X-ray spectrum. A fraction of these X-rays are absorbed by the ejecta walls and re-emitted as thermal radiation, leading to an optical/UV transient peaking at a luminosity of ~1e43-1e44 erg/s on a timescale of several hours to days. This is dimmer than predicted by simpler analytic models because the large optical depth of electron/positron pairs across the nebula suppresses the efficiency with which the magnetar spin down luminosity is thermalized. Nevertheless, the optical/UV emission is more than two orders of magnitude brighter than a radioactively powered `kilonova.' In some cases nebular X-rays are sufficiently luminous to re-ionize the ejecta, in which case non-thermal X-rays escape the ejecta unattenuated with a similar peak luminosity and timescale as the optical radiation. We discuss the implications of our results for the temporally extended X-ray emission that is observed to follow some short gamma-ray bursts (GRBs), including the kilonova candidates GRB 080503 and GRB 130603B.",
  "revisions": [
    {
      "version": "v1",
      "updated": "2013-11-06T21:00:30.000Z"
    }
  ],
  "analyses": {
    "keywords": [
      "binary neutron stars",
      "stable millisecond magnetars",
      "x-ray emission",
      "black hole",
      "case non-thermal x-rays escape"
    ],
    "tags": [
      "journal article"
    ],
    "publication": {
      "doi": "10.1093/mnras/stu247",
      "journal": "Monthly Notices of the Royal Astronomical Society",
      "year": 2014,
      "month": "Apr",
      "volume": 439,
      "number": 4,
      "pages": 3916
    },
    "note": {
      "typesetting": "TeX",
      "pages": 13,
      "language": "en",
      "license": "arXiv",
      "status": "editable",
      "inspire": 1263628,
      "adsabs": "2014MNRAS.439.3916M"
    }
  }
}