skip to main content

SciTech ConnectSciTech Connect

Title: DISTORTED CYCLOTRON LINE PROFILE IN CEP X-4 AS OBSERVED BY NuSTAR

We present spectral analysis of Nuclear Spectroscopic Telescope Array and Swift observations of Cep X-4 during its outburst in 2014. We observed the source once during the peak of the outburst and once during the decay, finding good agreement in the spectral shape between the observations. We describe the continuum using a power law with a Fermi–Dirac cutoff at high energies. Cep X-4 has a very strong cyclotron resonant scattering feature (CRSF) around 30 keV. A simple absorption-like line with a Gaussian optical depth or a pseudo-Lorentzian profile both fail to describe the shape of the CRSF accurately, leaving significant deviations at the red side of the line. We characterize this asymmetry with a second absorption feature around 19 keV. The line energy of the CRSF, which is not influenced by the addition of this feature, shows a small but significant positive luminosity dependence. With luminosities between (1–6) × 10{sup 36} erg s{sup −1}, Cep X-4 is below the theoretical limit where such a correlation is expected. This behavior is similar to Vela X-1 and we discuss parallels between the two systems.
Authors:
; ; ; ;  [1] ;  [2] ;  [3] ;  [4] ; ; ;  [5] ;  [6] ;  [7] ;  [8] ;  [9] ;  [10] ;  [11] ;  [12] ;  [13]
  1. Cahill Center for Astronomy and Astrophysics, California Institute of Technology, Pasadena, CA 91125 (United States)
  2. CRESST, Department of Physics, and Center for Space Science and Technology, UMBC, Baltimore, MD 21250 (United States)
  3. Inter-University Center for Astronomy and Astrophysics, Ganeshkhind, Pune 411007 (India)
  4. Osservatorio Astronomico di Cagliari, I-09047 Selargius (Italy)
  5. Space Sciences Laboratory, University of California, Berkeley, CA 94720 (United States)
  6. DTU Space, National Space Institute, Technical University of Denmark, DK-2800 Lyngby (Denmark)
  7. Massachusetts Institute of Technology, Kavli Institute for Astrophysics, Cambridge, MA 02139 (United States)
  8. Columbia Astrophysics Laboratory, Columbia University, New York, NY 10027 (United States)
  9. Department of Astronomy and Astrophysics, The Pennsylvania State University, University Park, PA 16802 (United States)
  10. European Southern Observatory, D-85748 Garching bei München (Germany)
  11. Jet Propulsion Laboratory, California Institute of Technology, Pasadena, CA 91109 (United States)
  12. Dr. Karl-Remeis-Sternwarte and ECAP, University of Erlangen-Nuremberg, D-96049 Bamberg (Germany)
  13. NASA Goddard Space Flight Center, Greenbelt, MD 20771 (United States)
Publication Date:
OSTI Identifier:
22518954
Resource Type:
Journal Article
Resource Relation:
Journal Name: Astrophysical Journal Letters; Journal Volume: 806; Journal Issue: 2; Other Information: Country of input: International Atomic Energy Agency (IAEA)
Country of Publication:
United States
Language:
English
Subject:
79 ASTROPHYSICS, COSMOLOGY AND ASTRONOMY; ABSORPTION; ACCRETION DISKS; CORRELATIONS; COSMIC X-RAY BURSTS; CYCLOTRON RESONANCE; KEV RANGE; LUMINOSITY; RESONANCE SCATTERING; STARS; TELESCOPES; X RADIATION