Time Variability of the Geocoronal Solar Wind Charge Exchange in the Direction of the Celestial Equator

TL;DR

This study detects time-variable X-ray emission from geocoronal solar wind charge exchange, correlating with solar wind flux, and suggests using X-ray observations to model Earth's neutral hydrogen and solar wind environment.

Contribution

It provides the first evidence of time variability in geocoronal SWCX emission and links it to solar wind flux, offering a new method to constrain Earth's neutral hydrogen distribution.

Findings

Detected strong, variable OVII line emission in X-ray spectra.

Found a significant correlation between line intensity and solar wind O7+ flux.

Proposed using X-ray data to model Earth's neutral hydrogen and solar wind distribution.

Abstract

We report the detection of a time variable OVII line emission in a deep 100 ks Suzaku X-ray Imaging Spectrometer spectrum of the Galactic Ridge X-ray emission. The observed line intensity is too strong (11+/-2 line unit or photon cm^-2 s^-1 str^-1) to be emitted inside the heavily obscured Galactic disk. It showed a factor of two time variation which shows a significant (~4 sigma) correlation with the solar wind O^7+ ion flux. The high line intensity and the good time correlation with the solar wind strongly suggests that it originated from geocoronal solar wind charge exchange emission. We discuss the X-ray line intensity considering a line of sight direction and also theoretical distribution models of the neutral hydrogen and solar wind around the Earth. Our results indicate that X-ray observationsof geocoronal solar wind charge exchange emission can be used to constrain these models.