Despite decades of observations, the nature of the hard X-ray/soft gamma-ray emission of Cen A, the brightestradio-loud AGN in the hard X-ray sky, is still unclear. The two main competing models are thermal Comptonizationand synchrotron self-Compton emission, and they predicted a spectral cutoff of roughly 300 keV or above 1 MeV,respectively and requires spectral coverage out to the MeV region to differentiate. INTEGRAL/SPI has spectral coverageto a few MeV and thus capability to constrain where the spectral cutoff occurs and assess the origin of the hardX-ray/soft gamma-ray emission. SPIs high energy resolution can also search for 511 keV annihilation features inthe spectrum on both short and long timescales. Motivated by this, we request a multi-year normal time proposal of3 Ms of exposure time in AO-19 and 3 Ms on exposure time in AO-20.
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.
European Space Agency, Rodi, 2026, 'CEN A: UNDERSTANDING THE NATURE OF THE HARD X-RAY/SOFT GAMMA-RAY EMISSION WITH INTEGRAL/SPI', 1.0, European Space Agency, https://doi.org/10.57780/esa-g4494n4
