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arXiv 1208.0169astro-ph.HE
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来自Swift-BAT硬X射线巡天的IGR J16493-4348中共振回旋线的证据

Evidence for a resonant cyclotron line in IGR J16493-4348 from the Swift-BAT hard X-ray survey

A. D'Aì, G. Cusumano, V. La Parola, A. Segreto, T. Di Salvo, R. Iaria, N. R. Robba

摘要:

共振吸收回旋特征是直接测量吸积中子星磁场强度的关键诊断工具。然而,回旋特征的典型值位于20 keV和50 keV之间的光谱的高能量部分,其中检测经常被来自单点观测的低统计数据所抑制。我们表明,长期的监测活动进行持续的,但微弱的,吸积高质量的X射线二进制的斯威夫特-BAT能够揭示在他们的光谱回旋特征的存在。我们从对高质量X射线源IGR J16493-4348进行的长达54个月的Swift-BAT调查中提取了平均Swift-BAT 15-150 keV光谱。为了限制宽带谱,我们使用来自Swift-XRT和朱雀点观测的软X射线谱。我们用一套描述吸积高质量X射线双星能谱的唯象模型来模拟能谱;无论我们使用哪种模型,我们都发现谱拟合有显着改进,为模型增加了广泛的(10 keV宽度)吸收特征,最佳拟合能量估计值在30和33 keV之间,我们认为这是共振回旋吸收特征的证据。我们还讨论了与使用Swift-BAT进行此类研究相关的工具问题,以及衡量这种检测置信水平的统计方法。修正了1.4 M $_{\sun}$中子星的引力红移后,推断出的表面磁场为Bsurf 3.7 x 10^{12}高斯。IGR J16493-4348的光谱参数符合经验的相关性时,观察到的高质量双星与检测到的回旋特征的整个样本被认为是。

英文摘要:

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 for 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 statistics from single pointed observations. 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. 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. 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 for a resonant cyclotron absorption feature. We also discuss instrumental issues related to the use of Swift-BAT for this kind of studies and the statistical method to weight the confidence level of this detection. Correcting for the gravitational redshift of a 1.4 M$_{\sun}$ neutron star, the inferred surface magnetic field is Bsurf 3.7 x 10^{12} 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.

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