Engineering topics

Brian Williams

Publications and source records attributed to Brian Williams.

3 records

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↗

NASA NTRSDate not supplied

Direct Measurement of the Ion Temperatures in Tycho's SNR

We present preliminary results of our XMM- Newton/RGS observation of the southeastern ejecta knots in Tycho's supernova remnant. The RGS successfully resolved numerous emission lines including O He-alpha, O Ly-alpha, and Fe L lines. Line broadening was measured to be ~3 eV for the O He-alpha and ~4.5 eV for Fe L lines. If we attribute the broadening to pure thermal Doppler effects, then we obtain kT_O and kT_Fe to be ~400 keV and 1.5 MeV, respectively. These temperatures can be explained by collisionless shock heating with a shock velocity of ~3600 km/s. This is inconsistent with (slightly smaller than) a forward shock speed of ~4300 km/s, suggesting that the knots are heated by a reverse shock. The relative abundance of intermediate-mass elements to oxygen in the knots is more consistent with that expected in a classical W7 model (a single-degenerate scenario) than a violent merger of two white dwarves (a double-degenerate scenario).

Brian Williams↗

NASA NTRSDate not supplied

Two Decades of Evolution in Tycho: An X-ray Perspective

Tycho’s supernova in 1572 was a pivotal event in the history of astronomy, showing that the heavens could no longer be considered fixed and unchanging. Four centuries later, we have decades of observations of the remnant from this supernova, which we can now watch evolve over the course of an astronomer’s career. In this talk, I will give a historical overview of the radio and X-ray observations of Tycho’s SNR, from which we can measure expansion velocities of both the forward shock and the ejecta. I will show that despite Tycho being circular in shape, the remnant is expanding asymmetrically, and may be decelerating rapidly in some locations. I will also discuss what the kinematics of the ejecta velocities tell us about the progenitor supernova system.

Brian Williams↗