Welcome to my webpage!

I'm a Support Scientist for the X-Ray Imaging and Spectroscopy Mission (XRISM)
at NASA Goddard Space Flight Center (Greenbelt, Maryland, USA).
On these pages you will find more about my activities, research interests, as well as a CV, a list of publications, and other (useful and less useful) things...


X-Ray Imaging and Spectroscopy Mission (XRISM) is an ambitious JAXA/NASA collaborative space mission (with participation from ESA), designed to explore the X-ray emission of our Universe like never before. On one hand, its spectrometer Resolve will "see" X-ray sources in the sky (massive stars, stellar and supermassive black holes, hot gas in clusters and group of galaxies, etc.) with an unprecedented spectral resolution of ~5 eV, which will revolutionize our understanding of astrophysics (at high energies but not only). On the other hand, its imager Extend will allow impressive mapping over a very large field-of-view spreading over 38 arcmin. Expected to be launched this year, the mission will fly in low-Earth orbit, ensuring low and stable background to maximize its scientific performances.

Located at NASA Goddard Space Flight Center, the XRISM Guest Observer Facility (GOF) will ensure continuous support to the general astrophysics community with the aim to facilitate all procedures related to XRISM observations and data analysis.

Research interests

About 80% of the total baryonic matter of the Universe is in the form of a very hot gas, glowing in X-ray wavelengths, and filling the very large gravitational well of clusters of galaxies. This so-called intra-cluster medium (ICM) contains not only primordial hydrogen and helium, but is rich in heavy elements (O, Mg, Si, S, Ca, Fe, Ni,...). These metals have been created by billions of supernovae within cluster galaxies since the major epoch of star formation (about 10-12 billion years ago), then spread out and accumulated over cosmic time into the ICM. When, where, and how did this chemical enrichment occur? And which types of supernovae are responsible for creating the metals we see today? Using X-ray observatories (e.g. XMM-Newton, Chandra, XRISM), I measure the abundance of these elements in galaxy clusters in order to answer these open questions.

Abell 4059

(credit: F.M.)

Cas A supernova

(credit: NASA/JPL-Caltech)

Abell 4038

(credit: F.M.)

Hydra A

(credit: Chandra X-ray obs.)


(credit: Chandra X-ray obs.)

Abell 85

(credit: F.M.)

Tycho supernova

(credit: NASA/CXC/Rutgers)


(credit: ESA)

Perseus cluster

(credit: NASA/CXC/IoA)


Born in Brussels (Belgium), 27 June 1989
Languages: French (native), English (fluent), Dutch (intermediate)

Academic positions

  • 2022-now - XRISM support scientist - NASA/GSFC, University of Maryland (USA)

  • 2019-2022 - Research Fellow - ESA/ESTEC (The Netherlands)

  • 2017-2019 - Postdoc - MTA/Eötvos University (Hungary)

  • 2017-2017 - Postdoc - Leiden University (The Netherlands)


  • 2013-2017 - PhD - High-energy Astrophysics, Leiden University/SRON (The Netherlands)

  • 2010-2012 - MSc - Space Sciences, University of Liège (Belgium)

  • 2007-2010 - BSc - Physics, Université Libre de Bruxelles (Belgium)

  • 2001-2007 - High school - Latin-Mathematics, Lycée Émile Jacqmain, Brussels (Belgium)


First author:


Scripts (etc.)

Here are some of my scripts, routines and tables you may find useful...

    - abunfit

    • Fits a set of intra-cluster abundances with a combination of supernova yield models. Several models (either SNcc or SNIa) are available and can be updated or created.


    /!\ If you use abunfit.py for a publication, please cite:
    Mernier, F., de Plaa, J., Pinto, C., et al. 2016b, A&A, 595, A126

    /!\ If you use the abundance measurements reported in abunfit/cluster/ for a publication, please cite:
    Mernier, F., de Plaa, J., Pinto, C., et al. 2016a, A&A, 592, A157

    /!\ If you use the supernova yields reported in abunfit/ for a publication, please cite the original papers accordingly.

    - SPEX (cie) vs. XSPEC (apec) comparison

    • These tables show the relative deviations of a given best-fit parameter (kT, Fe, O/Fe, Mg/Fe, Si/Fe, S/Fe) between the X-ray spectral models "cie" v3.0.5 (in the fitting package SPEX) and "(v)apec" v3.0.9 (in the fitting package XSPEC) expected for a collisionally ionized plasma at various assumed temperatures and metallicities. When you get a best-fit temperature or metal abundance value for your favourite galaxy cluster/group using your favourite spectral code, you can refer to these tables. They will give you an estimate of the current atomic/code-related uncertainties of your best-fit parameter.

    SPEX vs. XSPEC comparison tables

    /!\ If you use or refer to these numbers in a publication, please cite:
    Mernier, F., Werner, N., Lakhchaura, K., et al. 2019, Astron. Nachr., 341, 203


Science is for everyone, and thus should be accessible to everyone. We, astronomers, are in general supported by public fundings; therefore it is also our responsibility to “close the loop” by revealing citizens the beauty of the Universe, keeping young (and less young) minds curious, and show the necessity of science in everyday’s life.

Below you will find some slides I presented during outreach events; in particular for the astronomy youth camps "Jeunesse et Science" (Modave, Belgium), for Astronomy on Tap - Budapest, and for Astronomy on Tap - Leiden.

About me (outside astronomy)

Astronomy is great, so are many other activities.
I'm also into music (rock, pop, and/or jazz), and one of my favourite Sunday-afternoon activities is to play piano/keyboards (see my YouTube channel). I'm also into sports: (indoor) football, fencing, sometimes also swimming, biking, or simply running. And of course, always in for deep discussions about politics, society, and philosophy while enjoying a good (preferably Trappist!) beer.


NASA Goddard Space Flight Center
Building 34, Office W203,
8800 Greenbelt Rd,
Greenbelt, MD 20771 (USA)
Email 1: [firstname].[surname]@nasa.gov
Email 2: f[surname]@umd.edu
...where [firstname] is francois
...and [surname] is mernier