Volume 532, August 2011
|Number of page(s)||7|
|Section||Stellar structure and evolution|
|Published online||26 July 2011|
Evidence for a resonant cyclotron line in IGR J16493−4348 from the Swift-BAT hard X-ray survey
Dipartimento di Fisica, Università di Palermo, via Archirafi 36, 90123 Palermo, Italy
2 INAF, Istituto di Astrofisica Spaziale e Fisica Cosmica, via U. La Malfa 153, 90146 Palermo, Italy
Received: 6 April 2011
Accepted: 13 June 2011
Context. Resonant absorption cyclotron features are a key diagnostic tool to directly measure the strength of the magnetic field of accreting neutron stars. However, typical values of cyclotron features lie in the high-energy part of the spectrum between 20 keV and 50 keV, where detection is often damped by the low quality statistics of results derived from single pointed observations.
Aims. We show that long-term monitoring campaign performed with Swift-BAT of persistently, but faint, accreting high-mass X-ray binaries is able to reveal in their spectra the presence of cyclotron features.
Methods. We extracted the average Swift-BAT 15−150 keV spectrum from the 54 months long Swift-BAT survey of the high-mass X-ray source IGR J16493−4348. To constrain the broadband spectrum, we used soft X-ray spectra from Swift-XRT and Suzaku pointed observations.
Results. We model the spectra using a set of phenomenological models usually adopted to describe the energy spectrum of accreting high-mass X-ray binaries. Irrespective of the models we used, we found significant improvements in the spectral fits adding to the models a broad (10 keV width) absorption feature, with best-fitting energy estimate between 30 and 33 keV, that we interpret as evidence of a resonant cyclotron absorption feature. We also discuss possible instrumental biases related to the use of Swift-BAT for this kind of study and the statistical method to weight the confidence level of this detection. Correcting for the gravitational redshift of a 1.4 M⊙ neutron star, the inferred surface magnetic field is Bsurf ~ 3.7 × 1012 gauss. The spectral parameters of IGR J16493−4348 fit well with empirical correlations observed when the whole sample of high-mass binaries with detected cyclotron features is considered.
Key words: magnetic fields / line: profiles / X-rays: binaries / X-rays: individuals: IGR J16493−4348
© ESO, 2011
Current usage metrics show cumulative count of Article Views (full-text article views including HTML views, PDF and ePub downloads, according to the available data) and Abstracts Views on Vision4Press platform.
Data correspond to usage on the plateform after 2015. The current usage metrics is available 48-96 hours after online publication and is updated daily on week days.
Initial download of the metrics may take a while.