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

Journal Article · Sat Jun 20 00:00:00 EDT 2015 · Astrophysical Journal Letters

DOI:https://doi.org/10.1088/2041-8205/806/2/L24· OSTI ID:22518954

Fürst, F.; Miyasaka, H.; Harrison, F. A.; Tendulkar, S. P.; Walton, D. J. ^[1]; Pottschmidt, K. ^[2]; Bhalerao, V. ^[3]; Bachetti, M. ^[4]; Boggs, S. E.; Craig, W. W.; Tomsick, J. A. ^[5]; Christensen, F. E. ^[6]; Grinberg, V. ^[7]; Hailey, C. J. ^[8]; Kennea, J. A. ^[9]; Rahoui, F. ^[10]; Stern, D. ^[11]; Wilms, J. ^[12]; Zhang, W. W. ^[13]

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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)

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.

• OSTI ID: 22518954
• Journal Information: Astrophysical Journal Letters, Vol. 806, Issue 2; Other Information: Country of input: International Atomic Energy Agency (IAEA); ISSN 2041-8205
• Country of Publication: United States
• Language: English

Related Subjects

79 ASTROPHYSICS
COSMOLOGY AND ASTRONOMY
ABSORPTION
ACCRETION DISKS
CORRELATIONS
COSMIC X-RAY BURSTS
CYCLOTRON RESONANCE
KEV RANGE
LUMINOSITY
RESONANCE SCATTERING
STARS
TELESCOPES
X RADIATION