Cosmic ray detections on Gaia CCDs

Gaia’s Focal Plane Assembly (FPA) with its 106 CCDs acts as a single big radiation monitor in space. Apart from accumulated ionizing dose and proton fluence over the mission lifetime, transient events in form of cosmic ray background can give an indication of the radiation environment at Gaia’s operational orbit around the Sun-Earth Lagrange point 2 (SEL2).

High energy background particles can leave transient features in CCD data that often pollute images of astronomical sources. However, useful information on the radiation environment where the telescope is positioned can be retrieved from analysis of these features. To support the analysis of these characteristic charge trails in the images (in terms of deposited charge, angle of incidence and track length for example) a small data set is being made available here together with a technical note that describes the data release content and format in more detail.

The 152 Flexible Image Transport System (FITS) image files are subsets of the occasional engineering data from the readout process of the Basic Angle Monitor (BAM) CCDs acquired through the on-board Service Interface Function (SIF), which allows downlinking information otherwise discarded on-board before transmission. These BAM CCD images provide the most suitable data set, because of two reasons: (1) these are the only CCDs on board Gaia, which are operated in a stare mode with several seconds exposure time in addition to the nominal TDI readout mode, and (2) the particular readout window subsets contain apart from the cosmic rays no other external signal source but a relatively low and constant background that has been removed in a pre-processing step.

The complete data set covering data acquisitions from May 2014 to January 2015 and the corresponding technical note are available for download from the links below.

Full Technical Note

Data Files

If you make use of this data set, please use the following acknowledgement in any publications resulting from your work:

"This work has made use of a specially prepared data set from the ESA space mission Gaia. The raw data were processed by the Calibration Team at the ESA Gaia Science Operations Centre, making use also of systems developed by the Gaia Data Processing and Analysis Consortium (DPAC). Funding for the DPAC has been provided by national institutions, in particular the institutions participating in the Gaia Multilateral Agreement. The Gaia mission website is: https://www.cosmos.esa.int/gaia"

Extended data set: Cosmic ray detections on Gaia CCDs

In order to support more in-depth studies of the Gaia radiation environment, a dataset comprising of windows of charge trails from 15 of the CCDs (SM and BAM), as well as derived information on their characteristics and some auxiliary data has been gathered together. The dataset covers intermittent data acquisitions from a subset of these CCDS from January 2014 to January 2018. It is important to note that no astrometric information, nor any information at all from celestial sources, is contained in this dataset. The dataset was prepared at the Gaia Science Operations Center at ESA/ESAC in Madrid as part of a traineeship program. This work is part of the MSc thesis of Christian Kirsch (Remeis Observatory, Bamberg), which is available here.

For further details on the contents, or information on how to obtain this dataset, please contact the Gaia helpdesk.