Establishing HZ43 A, Sirius B, and RX J185635-3754 as soft X-ray standards: a cross-calibration between the Chandra LETG+HRC-S, the EUVE spectrometer, and the ROSAT PSPC
Establishing HZ43 A, Sirius B, and RX J185635-3754 as soft X-ray standards: a cross-calibration between the Chandra LETG+HRC-S, the EUVE spectrometer, and the ROSAT PSPC
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将 HZ43 A、Sirius B 和 RX J185635-3754 建立为软 X 射线标准：Chandra LETG HRC-S、EUVE 光谱仪和 ROSAT PSPC 之间的交叉校准
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发表时间：
2006
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通讯作者：
U. Tuebingen
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作者：
K. Beuermann;V. Burwitz;T. Astrophysik;U. Goettingen;H Germany;M. F. Physik;I. F. Astrophysik;U. Tuebingen
语境。软X射线范围内星载仪器的绝对校准很大程度上依赖于热白矮星的模型光谱。目标。我们分析了白矮星 HZ43 A 和天狼星 B 以及中子星 RX J185635−3754 的钱德拉 LETG+HRC 观测结果，旨在解决当前三颗恒星软 X 射线光谱通量和光球参数的不确定性。我们将导出的光子光谱应用于 LETG+HRC-S 与短波长 EUVE 光谱仪和 ROSAT PSPC 的交叉校准。方法。我们将 HZ43 A 与 44−48 A 范围内的 RX J1856 的通量联系起来，并对三颗恒星的 LETG+HRC 光谱进行同步最小二乘拟合。这使我们能够确定一组内部一致的光谱能量分布以及根据经验得出的对 LETG+HRC-S 有效面积的波长相关校正。我们对白矮星采用通过 TMAP 计算的 NLTE 模型大气，对 RX J1856 采用两黑体模型，与各自的光通量相关。结果。 RX J1856 的双黑体模型在较冷的恒星上有一个热点，产生 kTspot = 62.8 ± 0. 4e V 和 kTstar = 32.3 ± 0.7 eV，从无穷远看恒星角半径为 0.1371 ± 0.0010 km pc −1 。对于 HZ43 A，我们的拟合结果为 Teff = 51 126 ± 660 K 和 log g = 7.90 ± 0.080 (cgs)，具有反相关误差 (1-σ)，其中不仅包括拟合的统计不确定性，还包括系统不确定性。 HZ43AB 显示先前检测到的轫致辐射分量，其温度为 kT ± 0.6 keV。对于 Sirius B，我们发现 Teff = 24 923 ± 115 K，固定 log g = 8.6。短波长EUVE光谱仪的校准与LETG+HRC-S的校准相差15±7%。 ROSAT PSPC 被发现已正确校准，误差在百分之几以内，并且有关重大校准错误的报告是没有根据的。结论。我们获得了 RX J185635−3754、HZ43 A 和 Sirius B 的改进参数，这些参数适合从光学到软 X 射线区域的观测。我们的方法使我们能够引用它们在选定波长下的绝对光谱通量，这可能有助于其他星载仪器的校准。
Context. The absolute calibration of space-borne instruments in the soft X-ray regime rests strongly on model spectra of hot white dwarfs. Aims. We analyze the Chandra LETG+HRC observations of the white dwarfs HZ43 A and Sirius B and of the neutron star RX J185635−3754 with the aim of resolving current uncertainties in the soft X-ray spectral fluxes and photospheric parameters of the three stars. We apply the derived photon spectra to a cross-calibration of the LETG+HRC-S with the short-wavelength EUVE spectrometer and the ROSAT PSPC. Methods. We tie HZ43 A to the flux of RX J1856 in the 44−48 A range and perform a simultaneous least squares fit to the LETG+HRC spectra of the three stars. This allows us to determine an internally consistent set of spectral energy distributions and an empirically derived wavelength-dependent correction to the LETG+HRC-S effective area. We employ NLTE model atmospheres calculated with TMAP for the white dwarfs and a two-blackbody model for RX J1856, tied to the respective optical fluxes. Results. The two-blackbody model for RX J1856 features a hot spot on a cooler star and yields kTspot = 62.8 ± 0. 4e V and kTstar = 32.3 ± 0.7 eV with a stellar angular radius as seen from infinity of 0.1371 ± 0.0010 km pc −1 . For HZ43 A, our fit yields Teff = 51 126 ± 660 K and log g = 7.90 ± 0.080 (cgs) with anti-correlated errors (1-σ) which include not only the statistical but also the systematic uncertainties of the fit. HZ43AB displays a previously detected bremsstrahlung component with a temperature kT � 0.6 keV. For Sirius B, we find Teff = 24 923 ± 115 K for fixed log g = 8.6. The calibration of the short-wavelength EUVE spectrometer differs from that of the LETG+HRC-S by 15 ± 7%. The ROSAT PSPC is found to be correctly calibrated within a few percent and reports of a major miscalibration are unfounded. Conclusions. We have obtained improved parameters for RX J185635−3754, HZ43 A, and Sirius B which fit the observations from the optical to the soft X-ray regime. Our approach allows us to quote their absolute spectral fluxes at selected wavelengths which may aid the calibration of other space-borne instruments.