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PRODID:UW-Madison-Physics-Events
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SEQUENCE:2
UID:UW-Physics-Event-9059
DTSTART:20250129T180000Z
DTEND:20250129T200000Z
DTSTAMP:20260413T170702Z
LAST-MODIFIED:20250124T210525Z
LOCATION:6242 CH or https://uwmadison.zoom.us/j/91520312725?pwd=bCtnVG
 hybFhLOTRsQlJ1NkhnVmdWQT09
SUMMARY:A high-spectral resolution study of the galactic center soft X
 -ray bulge with the X-ray Quantum Calorimeter\, Thesis Defense\, Conje
 epuram V Ambarish\, Physics PhD Graduate Student
DESCRIPTION:The galactic center soft X-ray bulge\, clearly seen in the
  ROSAT all-sky survey map in the 0.44-1.2 keV band\, is one of the bri
 ghtest diffuse X-ray features in the sky in this energy range. The ext
 ended nature of the emission suggests that the source is likely hot ga
 s shock heated by supernovae. Deep shadows from molecular clouds at 2-
 4 kpc show that the soft X-ray bulge is not a local feature and is lik
 ely associated with either the galactic center or an inner spiral arm.
  The soft X-ray bulge has been studied previously with ROSAT and Suzak
 u\, but with their energy resolution of ~ 300 eV and 60 eV respectivel
 y\, they are only able to separate bulge emission from at least four f
 oreground and background emission components without resorting to high
 ly oversimplified models.
\nThe X-ray quantum calorimeter (XQC) is a s
 ounding rocket instrument with silicon thermistor microcalorimeters op
 erated at 50 mK. With a detector area of 1.44 cm2 mechanically collima
 ted to a 60 degree field of view\, XQC has a high throughput (~ 1 cm2 
 sr) and an energy resolution of ~ 8 eV FWHM below 1 keV. Since the sof
 t X-ray bulge is too far south to observe from NASA’s usual launch s
 ite at White Sands Missile Range (WSMR)\, XQC was part of NASA’s lon
 g-awaited campaign to Australia\, where we had a successful flight to 
 observe the bulge.
\nI present here a high resolution spectrum with cl
 early resolved lines from multiple ionization states of carbon\, nitro
 gen\, oxygen\, neon and iron. A model-independent analysis of ratios o
 f fluxes from these lines requires emission from a minimum of three th
 ermal components at ~ 1\,2\, and 8 MK. I show that our spectrum is con
 sistent with emission from either an adiabatic polytrope filling the i
 nner galaxy or an isothermal halo at ~ 2 MK\, both with additional X-r
 ay emission from unresolved stars.
\nAn alternative explanation for th
 e soft X-ray bulge could be a series of blowouts from star-forming reg
 ions in the inner spiral arm. The relative abundance estimates from th
 e observation\, particularly the Fe/O ratio\, are used to distinguish 
 between a galactic bulge or a spiral arm origin for the hot gas since 
 these two regions should be dominated by different types of supernovae
 \, type Ia and type II respectively. The metal yields of the two are d
 istinct with Type Ia producing mostly iron and Type II producing oxyge
 n and other alpha elements. Our fits indicate an Fe/O ratio of about t
 wice the solar value\, favoring enrichment by Type Ia supernova and a 
 galactic bulge origin for the hot gas.
URL:https://www.physics.wisc.edu/events/?id=9059
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