Confirmation of a High Magnetic Field in GRO J1008-57

Abstract

GRO J1008$-$57 is a high-mass X-ray binary for which several claims of a cyclotron resonance scattering feature near 80 keV have been reported. We use NuSTAR, Suzaku, and Swift data from its giant outburst of November 2012 to confirm the existence of the 80 keV feature and perform the most sensitive search to date for cyclotron scattering features at lower energies. We find evidence for a 78${}_{-2}^{+3}$ keV line in the NuSTAR and Suzaku data at $>4\sigma$ significance, confirming the detection using Suzaku alone by Yamamoto et al. (2014). A search of both the time-integrated and phase-resolved data rules out a fundamental at lower energies with optical depth larger than 5% of the 78 keV line. These results indicate that GRO J1008$-$57 has a magnetic field of $6.7\times 10^{12}(1+z)$ G, the highest of known accreting pulsars.

Submitted to the Astrophysical Journal. 8 pages, 6 figures, 3 tables

References in corpus (4)

• A model for cyclotron resonance scattering features
• Line Searches in Swift X-ray Spectra
• Now you see it, now you don't - the circumstellar disk in the GRO J1008--57 system
• NuSTAR J033202-2746.8: direct constraints on the Compton reflection in a heavily obscured quasar at z~2

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• Relation of cyclotron resonant energy and luminosity in a strongly magnetized neutron star GRO J1008-57 observed by Insight-HXMT
• Insight-HXMT firm detection of the highest energy fundamental cyclotron resonance scattering feature in the spectrum of GRO J1008-57
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