The future of high-resolution spectroscopy

Project Leader

The XRISM Observatory is a joint JAXA / NASA / ESA X-ray spectrometer that will launch in early 2022. XRISM will revolutionize how we understand accreting supermassive black holes, starting from how cold gas flows in from the interstellar medium of the galaxy, down to the inner accretion flow where matter is affected by the strong gravity of the black hole. This gravitational inflow leads to massive outflows, which may be powerful enough to prevent gas from cooling to form stars, thus affecting the evolution of the host galaxy. X-ray continuum emission is produced within a few gravitational radii of the central black hole and irradiates the remaining infalling or outflowing gas (e.g. the accretion disc, broad-line region clouds or the dusty torus), producing a plethora of emission features, known colloquially as the reflection spectrum. The Fe line is the most commonly used diagnostic of the structure around the AGN because it is an abundant element that appears in a relatively isolated region of the spectrum. XRISM will provide an unprecedented view of this important spectral feature.

Left: A comparison of XRISM to some of our current best instruments. XRISM will have vastly better sensitivity than the high resolution gratings on Chandra, and will have far superior energy resolution than the CCDs on XMM-Newton. This will help break degeneracies between different models of the emission from the inner accretion flow around AGN. Middle: An example of such a degeneracy in the XMM-pn spectra of MCG-6-30-15. The pn spectrum can be equally well described by pure relativistic reflection with an inclination of 5 deg (as shown in blue) or by relativistic reflection with an inclination of 75 deg with additional emission and absorption, including an ultrafast outflow of ∼ 0.13c (as shown in red). Right: XRISM will easily distinguish between these two scenarios, as the narrow emission and absorption will be resolved.

Team Members