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Ehud Behar

Publications and source records attributed to Ehud Behar.

6 records
All sourcesNASA NTRSDOE OSTI
NASA NTRS2024

Erratum: A NICER Viewing Angle on the Accretion Stream of Vela X-1 (2023 ApJ 950 170)

When this correction is applied to the model appearing in Figure 7, the overprediction of the Fe Kα flux vanishes and is replaced by a persistent underprediction at all phases. A corrected version of Figure 7 is given below (Figure 7). This corrected result is consistent with previous results by S. Watanabe et al. (2006). This correction does not invalidate the paper’s conclusions regarding additional reflection from the accretion stream. Rather, it is now apparent that the companion alone cannot account for the emission in any phase. This reinforces the role of the accretion stream as the most likely candidate for the observed emission lines. The exact contribution from the stream likely depends on how much of the stream is visible at each phase. We expect higher contributions around phases 0.35 and 0.65. In Figure 7 the highest accretion stream contribution is between 0.3–0.4 and around 0.7. Short observations of other fluorescence lines are required to study the geometry of the accretion stream further.

Roi Rahin↗
NASA NTRS2021

Modeling Magnetic Disk Wind State Transitions in Black Hole X-Ray Binaries

We analyze three prototypical black hole X-ray binaries, 4U 1630–472, GRO J1655–40, and H1743–322, in an effort to systematically understand the intrinsic state transition of the observed accretion disk winds between wind-on and wind-off states by utilizing state-of-the-art Chandra/HETGS archival data from multi-epoch observations. We apply our magnetically driven wind models in the context of magnetohydrodynamic(MHD)calculations to constrain(1)their global density slope(p),(2)their density (n17) at the foot point of the inner most launching radius, and(3)the abundances of heavier elements(AFe,S,Si). Incorporating the MHD winds into xstar photoionization calculations in a self-consistent manner, we create a library of synthetic absorption spectra given the observed X-ray continua. Our analysis clearly indicates a characteristic bimodal transition of multi-ion X-ray winds; i.e., the wind density gradient is found to steepen(fro mp∼1.2–1.4 to∼1.4–1.5)while its density normalization declines as the source transitions from the wind-onto the wind-off state. The model implies that the ionized wind remains physically present even in the wind-off state, despite its apparent absence in the observed spectra. Super solar abundances for heavier elements are also favored. Our global multi-ion wind models, taking into account soft X-ray ions as well as Fe K absorbers, show that the internal wind condition plays an important role in wind transitions besides photoionization changes. Simulated XRISM/Resolve and Athena/X-IFU spectra are presented to demonstrate a high fidelity of the multi-ion wind model for a better understanding of these powerful ionized winds in the coming decades

Keigo Fukumura↗
NASA NTRS2020

Planning In-Flight Calibration for XRISM

The XRISM X-ray observatory will fly two advanced instruments, the Resolve high-resolution spectrometer and the Xtend wide-field imager. These instruments, particularly Resolve, pose calibration challenges due to the unprecedented combination of spectral resolution, spectral coverage, and effective area, combined with a need to characterize the imaging fidelity of the full instrument system to realize the mission’s ambitious science goals. We present the status of the XRISM in-flight calibration plan, building on lessons from Hitomi and other X-ray missions. We present a discussion of targets and observing strategies to address the needed calibration measurements, with a focus on developing methodologies to plan a thorough and flexible calibration campaign and provide insight on calibration systematic error. We also discuss observations that exploit Resolve’s spectral resolution to calibrate atomic codes, and cross-calibration between the XRISM instruments and with other observatories.

Eric D Miller↗