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A High Spectral Resolution Observation of the Galactic Center Soft X-ray Bulge

Presentation #128.03 in the session Molecular Clouds, HII Regions, Interstellar Medium I.

Published onJul 01, 2023
A High Spectral Resolution Observation of the Galactic Center Soft X-ray Bulge

The ROSAT maps in the 0.5-1 keV range, characteristic of 1.5-3.5 x 106 K gas, show a very bright region about 30° radius around the Galactic center. It is strongly affected by intervening absorption and the superposition of unrelated features, particularly north of the plane, but can be rather well fit, both spatially and spectrally, by a simple adiabatic polytrope sitting in the gravitational potential well of the Galaxy. An alternative explanation is that it might be a chain of blowouts from star-forming regions along the inner spiral arm of the Galaxy, which has a similar extent.

Both models predict the presence of multiple phases at different temperatures, which is confirmed by Suzaku and XMM-Newton observations from the region showing evidence of components ranging from 1.5 - 4 x 106 K. Disentangling these observations to determine the physical state and relative abundances in the different components requires better spectral resolution than exists in current CCD detectors.

We present a preliminary spectrum of the southern part of the bulge (l= 350°, b= –15°) as the first attempt to distinguish these models with high spectral resolution detectors. The spectrum is from a five-minute sounding rocket flight of the University of Wisconsin-Madison/Goddard Space Flight Center X-ray Quantum Calorimeter (XQC) instrument, which launched from Arnhem Space Center in Australia’s Northern Territory, on June 26, 2022. This instrument has an array of microcalorimeter detectors with HgTe absorbers and doped silicon thermistors that operate at 50 mK. The detectors are sensitive from ~.07 - 7 keV, with a ~8 eV FWHM energy resolution below 1 keV, and ~1600 cm2 deg2 throughput at 600 eV. Furthermore, the total detector area, 1.4 cm2, is mechanically collimated to a 60° diameter field of view. With this large throughput and high spectral resolution, our spectrum shows lines of most of the astrophysically abundant elements, including oxygen and several ionization states of iron.

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