The defocused observations of bright sources with Athena /X-IFU

Kammoun ES, Barret D, Peille P, Willingale R, Dauser T, Wilms J, Guainazzi M, Miller JM (2022)

Publication Type: Journal article

Publication year: 2022

Journal

Astronomy & Astrophysics EDP Sciences

Book Volume: 664

Article Number: A29

DOI: 10.1051/0004-6361/202243606

Abstract

Context. The X-ray Integral Field Unit (X-IFU) is the high resolution X-ray spectrometer of ESA's Athena X-ray observatory. It will deliver X-ray data in the 0.2- 12 keV band with an unprecedented spectral resolution of 2.5 eV up to 7 keV. During the observation of very bright X-ray sources the X-IFU detectors will receive high photon rates. The count rate capability of the X-IFU will be improved by using the defocusing option, which will enable the observations of extremely bright sources with fluxes up to 1 Crab. In the defocused mode, the point spread function (PSF) of the telescope will be spread over a large number of pixels. In this case each pixel receives a small fraction of the overall flux. Due to the energy dependence of the PSF, this mode will generate energy-dependent artefacts increasing with count rate if not analysed properly. To account for the degradation of the energy resolution with pulse separation in a pixel, a grading scheme (of four grades) will be defined to realize the proper energy response to each event. This will create selection effects preventing the use of the nominal auxiliary response file (ARF) for all events. Aims. We present a new method for the reconstruction of the spectra obtained from observations performed with a PSF that varies as a function of energy. We apply our method to the case of the X-IFU spectra obtained during the defocused observations. Methods. We used the end-to-end SIXTE simulator to model defocused X-IFU observations. Then we estimated a new ARF for each of the grades by calculating the effective area at the level of each pixel. Results. Our method allows us to successfully reconstruct the spectra of bright sources when employed in the defocused mode, without any bias. Finally, we address how various sources of uncertainty related to our knowledge of the PSF as a function of energy affect our results.

Authors with CRIS profile

Thomas Dauser Dr.Karl-Remeis-Sternwarte Bamberg, Astronomisches Institut Jörn Wilms Lehrstuhl für Astronomie und Astrophysik

Involved external institutions

Université Toulouse III - Paul Sabatier FR France (FR) National Centre for Space Studies / Centre national d'études spatiales (CNES) FR France (FR) University of Leicester GB United Kingdom (GB) European Space Research and Technology Centre (ESTEC, ESA) NL Netherlands (NL) University of Michigan US United States (USA) (US)

How to cite

APA:

Kammoun, E.S., Barret, D., Peille, P., Willingale, R., Dauser, T., Wilms, J.,... Miller, J.M. (2022). The defocused observations of bright sources with Athena /X-IFU. Astronomy & Astrophysics, 664. https://dx.doi.org/10.1051/0004-6361/202243606

MLA:

Kammoun, E. S., et al. "The defocused observations of bright sources with Athena /X-IFU." Astronomy & Astrophysics 664 (2022).

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