An investigation into the effect of exposing XMM–Newton’s Optical Monitor to the light of Jupiter

Abstract

Abstract After nearly 18 yr of successful and safe operations, on 2017 July 17 and 18, XMM–Newton’s Optical Monitor (OM) observed Jupiter – an object 10 magnitudes brighter than safe brightness limits – in its visual (V) filter. The object was exposed 40 arcsec from the nominal European Photon Imaging Cameras pn boresight in the negative Y direction, creating a patch of depleted sensitivity. Two exposures of 4000 s each in the V filter left the sensitivity depleted in an area 70 by 40 arcsec; with the decrease in throughput varying from 34 per cent in the V filter to 15 per cent in the ultraviolet bands, but reaching a depth of 45 per cent in flat-field exposures. The wavelength dependency suggests the majority of the detector damage is due to loss of sensitivity in the photocathode from damage inflicted by ion feedback, while up to 15 per cent could be due to gain depletion of the MCP. The physical mechanisms causing the damage to the detector are discussed as well as possible solutions and opportunities that exist for the future operation of the OM.