Discovery of a Cyclotron Resonance Feature in the X-ray Spectrum of GX 304-1 with RXTE and Suzaku during Outbursts Detected by MAXI in 2010

Abstract

We report the discovery of a cyclotron resonance scattering feature (CRSF) in the X-ray spectrum of GX 304-1, obtained by RXTE and Suzaku during major outbursts detected by MAXI in 2010. The peak intensity in August reached 600 mCrab in the 2-20 keV band, which is the highest ever observed from this source. The RXTE observations on more than twenty occasions and one Suzaku observation revealed a spectral absorption feature at around 54 keV, which is the first CRSF detection from this source. The estimated strength of surface magnetic field, $4.7\times 10^{12}$ G, is one of the highest among binary X-ray pulsars from which CRSFs have ever been detected. The RXTE spectra taken during the August outburst also suggest that the CRSF energy changed over 50-54 keV, possibly in a positive correlation with the X-ray flux. The behavior is qualitatively similar to that observed from Her X-1 on long time scales, or from A 0535+26, but different from the negative correlation observed from 4U 0115+63 and X 0331+53.

7 pages, 4 figures, accepted for publication in PASJ

References in corpus (7)

• Gas Slit Camera (GSC) onboard MAXI on ISS
• Discovery of a flux-related change of the cyclotron line energy in Her X-1
• In-Orbit Performance of MAXI Gas Slit Camera (GSC) on ISS
• A Further Study of the Luminosity-Dependent Cyclotron Resonance Energies of the Binary X-ray Pulsar 4U0115+63 with RXTE
• Cyclotron Line Variability
• The pre-outburst flare of the A 0535+26 August/September 2005 outburst
• The appearance of magnetospheric instability in flaring activity at the onset of X-ray outbursts in A0535+26

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