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Broad-band observations of the Be/X-ray binary pulsar RX J0440.9+4431: discovery of a cyclotron absorption line

Authors

  • S. S. Tsygankov,

    Corresponding author
    1. Finnish Centre for Astronomy with ESO (FINCA), University of Turku, Väisäläntie 20, FI-21500 Piikkiö, Finland
    2. Astronomy Division, Department of Physics, University of Oulu, FI-90014 Oulu, Finland
    3. MPI for Astrophysics, Karl-Schwarzschild Str. 1, 85741 Garching, Germany
    4. Space Research Institute of the Russian Academy of Sciences, Profsoyuznaya Str. 84/32, Moscow 117997, Russia
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  • R. A. Krivonos,

    1. MPI for Astrophysics, Karl-Schwarzschild Str. 1, 85741 Garching, Germany
    2. Space Research Institute of the Russian Academy of Sciences, Profsoyuznaya Str. 84/32, Moscow 117997, Russia
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  • A. A. Lutovinov

    1. Astronomy Division, Department of Physics, University of Oulu, FI-90014 Oulu, Finland
    2. Space Research Institute of the Russian Academy of Sciences, Profsoyuznaya Str. 84/32, Moscow 117997, Russia
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E-mail: tsygankov@iki.rssi.ru

ABSTRACT

We report the results of an analysis of data obtained with the International Gamma-Ray Astrophysics Laboratory (INTEGRAL), Swift and Rossi X-ray Timing Explorer (RXTE) observatories during the 2010 April and September outbursts of the X-ray pulsar RX J0440.9+4431. The temporal and spectral properties of the pulsar in a wide energy band (0.6–120 keV) were studied for the first time. We discovered a ∼32-keV cyclotron resonant scattering feature in the source spectrum that allowed us to estimate the magnetic field strength of the neutron star as B≃ 3.2 × 1012 G. The estimate of the magnetic field strength was confirmed by a comprehensive analysis of the noise power spectrum of the source. Based on the recurrence time between Type I outbursts, the orbital period of the binary system can be estimated as ∼155 d. We have shown that the pulse profile has a sinusoidal-like single-peaked shape and has practically no dependence on the source luminosity or energy band.

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