{
  "id": "2309.17013",
  "version": "v1",
  "published": "2023-09-29T06:53:28.000Z",
  "updated": "2023-09-29T06:53:28.000Z",
  "title": "Long-term evolution of Cyclotron Line energy in an eclipsing pulsar 4U 1538-522",
  "authors": [
    "Ruchi Tamang",
    "Manoj Ghising",
    "Mohammed Tobrej",
    "Binay Rai",
    "Bikash Chandra Paul"
  ],
  "comment": "Accepted for publication in MNRAS, 11 pages, 12 figures",
  "doi": "10.1093/mnras/stad2907",
  "categories": [
    "astro-ph.HE"
  ],
  "abstract": "We present the timing and spectral analysis of the HMXB source 4U 1538-522 using NuSTAR observations. One of the observations partially covers the X-ray eclipse of the source along with eclipse ingress. The source is found to spin down at the rate of 0.163 $\\pm$ 0.002 s $\\text{yr}^{-1}$ between $\\sim$ (54973-58603) MJD. It is evident that at time $\\sim$ 58620 MJD, a torque reversal occurred, thereafter the source exhibited a spin-up trend at the rate - (0.305 $\\pm$ 0.018) s $\\text{yr}^{-1}$ until 59275 MJD. A recent NuSTAR observation finds the pulse period of the source: (526.2341 $\\pm$ 0.0041) s. The pulse profile exhibits a transition from double-peaked to single-peaked nature above $\\sim$ 30 keV. We analyzed the overall trend of the temporal evolution of fundamental Cyclotron Resonance Scattering Feature (CRSF), $\\text{E}_\\text{cyc}$, incorporating recent NuSTAR measurements. Initially, during the time span $\\sim$ (50452.16-55270.8) MJD, the cyclotron line energy is found to increase at a rate of 0.11 $\\pm$ 0.03 keV $\\text{yr}^{-1}$ which is further followed by a decrease at a rate - 0.14 $\\pm$ 0.01 keV $\\text{yr}^{-1}$ between (55270.8-59267) MJD. The combined measurements in the time span (50452.16-59267) MJD reveal that the cyclotron line energy is increasing linearly at a rate of 0.08 $\\pm$ 0.02 keV $\\text{yr}^{-1}$.",
  "revisions": [
    {
      "version": "v1",
      "updated": "2023-09-29T06:53:28.000Z"
    }
  ],
  "analyses": {
    "keywords": [
      "cyclotron line energy",
      "eclipsing pulsar 4u",
      "long-term evolution",
      "time span",
      "fundamental cyclotron resonance scattering feature"
    ],
    "tags": [
      "journal article"
    ],
    "note": {
      "typesetting": "TeX",
      "pages": 11,
      "language": "en",
      "license": "arXiv",
      "status": "editable"
    }
  }
}