While INTEGRAL instruments typically observe Galactic sources on the hundreds to thousands of pc scale, the closest vicinity to Earth, the solar system, has received almost no attention from INTEGRAL in its more than 18 yr mission life time. So far, the Earth had been used as an occulting object to measure the cosmic X-ray background. During one such observation, IBIS could observe auroral X-ray emission from Earth in real time, showing the interactions of the solar wind with the magnetic field of Earth. Such auroral emission has also been measured from Jupiter, and found to not only be powered by solar activity, but by the planet itself. Venus is also a known X-ray source. Lacking strong magnetic field and subsequently a pronounced magnetosphere, Venus produces X-ray emission with atmospheric fluorescence as it is illuminated by Solar X-rays, by Solar Wind Charge Exchange Mechanism (SWCX), or possibly by other currently poorly understood unknown processes. Most of the phenomena are restricted to photon energies of few keV, but electron bremsstrahlung can be expected up to the hard X-ray regime as suggested from a population of relativistic electrons in the Jupiter system. A significant contribution to the diffuse emission above 100 keV comes from the interaction of cosmic rays (CRs) with asteroids in the Main Belt (MB) between Mars and Jupiter as well as from Kuiper Belt Objects (KBOs) Especially at the 511 keV line, such a contribution from the ecliptic may result in false inferences for the size of and flux from the bulge, halo, and disk. We propose an observation program of the ecliptic to constrain the hard X-ray emission from Venus and Jupiter, and to better estimate the foreground emission from the solar system M-NM-3-ray albedo. This proposal is a replacement and an extension of a multi-year proposal accepted in AO18 (PI: T. Siegert) and AO19. The present proposal differs primarily by adding Venus.
The INTEGRAL (International Gamma-Ray Astrophysics Laboratory) mission, launched by the European Space Agency (ESA) on October 17, 2002, was designed to study high-energy phenomena in the universe. INTEGRAL was operating until february 2025 and it was equipped with three high-energy instruments: the Imager on Board the INTEGRAL Satellite (IBIS), the Spectrometer on INTEGRAL (SPI), and the JEM-X (Joint European Monitor for X-rays). Its Optical Monitoring Camera (OMC) provided optical V-band magnitude measurements, complementing the high-energy observations.
