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

F. Fürst; K. Pottschmidt; H. Miyasaka; V. Bhalerao; M. Bachetti; S. E. Boggs; F. E. Christensen; W. W. Craig; V. Grinberg; C. J. Hailey; F. A. Harrison; J. A. Kennea; F. Rahoui; D. Stern; S. P. Tendulkar; J. A. Tomsick; D. J. Walton; J. Wilms; W. W. Zhang

doi:10.1088/2041-8205/806/2/L24

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

F. Fürst, K. Pottschmidt, H. Miyasaka, V. Bhalerao, M. Bachetti, S. E. Boggs, F. E. Christensen, W. W. Craig, V. Grinberg, C. J. Hailey, F. A. Harrison, J. A. Kennea, F. Rahoui, D. Stern, S. P. Tendulkar, J. A. Tomsick, D. J. Walton, J. Wilms, W. W. Zhang

Astronomy & Astrophysics

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Abstract

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) × 10³⁶ erg s^-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.

Original language	English (US)
Article number	L24
Journal	Astrophysical Journal Letters
Volume	806
Issue number	2
DOIs	https://doi.org/10.1088/2041-8205/806/2/L24
State	Published - Jun 20 2015

All Science Journal Classification (ASJC) codes

Astronomy and Astrophysics
Space and Planetary Science

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10.1088/2041-8205/806/2/L24

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Fürst, F., Pottschmidt, K., Miyasaka, H., Bhalerao, V., Bachetti, M., Boggs, S. E., Christensen, F. E., Craig, W. W., Grinberg, V., Hailey, C. J., Harrison, F. A., Kennea, J. A., Rahoui, F., Stern, D., Tendulkar, S. P., Tomsick, J. A., Walton, D. J., Wilms, J., & Zhang, W. W. (2015). DISTORTED CYCLOTRON LINE PROFILE IN CEP X-4 AS OBSERVED BY NuSTAR. Astrophysical Journal Letters, 806(2), [L24]. https://doi.org/10.1088/2041-8205/806/2/L24

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title = "DISTORTED CYCLOTRON LINE PROFILE IN CEP X-4 AS OBSERVED BY NuSTAR",

abstract = "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) × 1036 erg s-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.",

author = "F. F{\"u}rst and K. Pottschmidt and H. Miyasaka and V. Bhalerao and M. Bachetti and Boggs, {S. E.} and Christensen, {F. E.} and Craig, {W. W.} and V. Grinberg and Hailey, {C. J.} and Harrison, {F. A.} and Kennea, {J. A.} and F. Rahoui and D. Stern and Tendulkar, {S. P.} and Tomsick, {J. A.} and Walton, {D. J.} and J. Wilms and Zhang, {W. W.}",

year = "2015",

month = jun,

day = "20",

doi = "10.1088/2041-8205/806/2/L24",

language = "English (US)",

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journal = "Astrophysical Journal Letters",

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Fürst, F, Pottschmidt, K, Miyasaka, H, Bhalerao, V, Bachetti, M, Boggs, SE, Christensen, FE, Craig, WW, Grinberg, V, Hailey, CJ, Harrison, FA, Kennea, JA, Rahoui, F, Stern, D, Tendulkar, SP, Tomsick, JA, Walton, DJ, Wilms, J & Zhang, WW 2015, 'DISTORTED CYCLOTRON LINE PROFILE IN CEP X-4 AS OBSERVED BY NuSTAR', Astrophysical Journal Letters, vol. 806, no. 2, L24. https://doi.org/10.1088/2041-8205/806/2/L24

TY - JOUR

T1 - DISTORTED CYCLOTRON LINE PROFILE IN CEP X-4 AS OBSERVED BY NuSTAR

AU - Fürst, F.

AU - Pottschmidt, K.

AU - Miyasaka, H.

AU - Bhalerao, V.

AU - Bachetti, M.

AU - Boggs, S. E.

AU - Christensen, F. E.

AU - Craig, W. W.

AU - Grinberg, V.

AU - Hailey, C. J.

AU - Harrison, F. A.

AU - Kennea, J. A.

AU - Rahoui, F.

AU - Stern, D.

AU - Tendulkar, S. P.

AU - Tomsick, J. A.

AU - Walton, D. J.

AU - Wilms, J.

AU - Zhang, W. W.

PY - 2015/6/20

Y1 - 2015/6/20

N2 - 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) × 1036 erg s-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.

AB - 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) × 1036 erg s-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.

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U2 - 10.1088/2041-8205/806/2/L24

DO - 10.1088/2041-8205/806/2/L24

M3 - Article

AN - SCOPUS:84937567984

SN - 2041-8205

VL - 806

JO - Astrophysical Journal Letters

JF - Astrophysical Journal Letters

IS - 2

M1 - L24

ER -

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

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