The Athena X-ray Observatory: Community Support Portal

  • Athena: revealing the Hot and Energetic Universe

    Athena: revealing the Hot and Energetic Universe

  • Where are the hot baryons and how do they evolve?

  • Reveal the causes and effects of cosmic feedback

  • Track obscured accretion through the epoch of galaxy formation

  • Understand the physics of accretion onto compact objects

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Athena papers

"Magnetic Shielding of Soft Protons in Future X-Ray Telescopes: The Case of the Athena Wide Field Imager", by V. Fioretti et al.

V FIoretti

By Valentina Fioretti (INAF OAS, Bologna, Italy)

Interplanetary space and Earth’s magnetosphere are both populated by low-energy (<300 keV) protons that are potentially able to scatter on the reflecting surface of the optics of X-ray focusing telescopes and reach the focal plane. Given Athena’s large effective area (1.4 m2 at 1 keV), the minimization of the contamination from soft protons is a key for performing observations at the sensitivity limit. Examples are surveys for faint high-z super-massive black holes or studies of the extended thermal emission in clusters of galaxies, among the main scientific goals of the Wide Field Imager (WFI) detector. For this reason, the WFI is the best case study for evaluating the soft proton induced X-ray background and the shielding efficiency of a magnetic diverter that deflects protons away from the field of view.

We find for all plasma regimes encountered in either L1 or L2 orbits that without a magnetic diverter, protons are indeed funnelled toward the focal plane well in excess of the requirement set by the Athena science objectives (5 × 10−4 cnt cm−2 s−1 keV−1 in 2 – 7 keV). This strongly suggests the use of a proton diverter as a shielding system on board Athena and all high-throughput X-ray telescopes operating in the interplanetary space. For a magnetic field computed to deflect 99% of the protons that would otherwise reach the WFI, Geant4 simulations show that this configuration, in the assumption of a uniform field, would efficiently shield the focal plane, yielding a residual background level of order or below the requirement.

Read full document.

"Athena X-IFU synthetic observations of galaxy clusters to probe the chemical enrichment of the Universe", by E. Cucchetti et al.


By Edoardo Cucchetti (IRAP, Toulouse, France)

What are we made of? Most of the atoms and elements we know of are formed within stars, either during their life (winds) or during powerful end-of-life phenomena called supernovae. In fact, different mechanisms of metal creation exist in the Universe and elements were not formed evenly during its history. To investigate this chemical enrichment, one must look in the X-rays at the hot gas within clusters of galaxies – the intra cluster medium (ICM) – which is continuously enriched through time by the billions of stars contained in its galaxies. However, to perform meaningful studies of the enrichment through cosmic time, a combination of a high-resolution spatially-resolved spectroscopy and a large telescope collective area is required. For this reason, the Athena/X-IFU will be the breakthrough instrument to investigate metal formation and circulation in the Universe.

In this paper, we tested the power of the X-IFU to fulfil this specific science objective. Using a set of simulated clusters derived from hydrodynamical simulations, we performed synthetic observations of this sample of objects through time, up to a redshift z=2 (10.4 billion years ago) with a completely realistic set-up (including e.g., background, instrumental effects). We demonstrated that with routine 100 ks observations, the X-IFU will be able to study the enrichment with unprecedented accuracy out to the outskirts of the clusters and provide solid answers to the origin of their metal content.

This work is paramount in the Athena context, as it shows the power of the mission in answering some of the key astrophysical questions of our time. It also serves as a feasibility study of the X-IFU, consolidating the current design and the need for spatially-resolved high-resolution spectroscopy.

Read full document.

"X-ray Structure between the Innermost Disk and Optical Broad Line Region in NGC 4151", by J. M. Miller et al.


We present an analysis of the narrow Fe K-alpha line in Chandra/HETGS observations of the Seyfert AGN, NGC 4151. The sensitivity and resolution afforded by the gratings reveal asymmetry in this line. Models including weak Doppler boosting, gravitational red-shifts, and scattering are generally preferred over Gaussians at the 5 sigma level of confidence, and generally measure radii consistent with R ~ 500-1000 GM/c^2. Separate fits to "high/unobscured" and "low/obscured" phases reveal that the line originates at smaller radii in high flux states; model-independent tests indicate that this effect is significant at the 4-5 sigma level. Some models and Delta t ~ 2 E+4 s variations in line flux suggest that the narrow Fe K-alpha line may originate at radii as small as R ~ 50-130 GM/c^2 in high flux states. These results indicate that the narrow Fe K-alpha line in NGC 4151 is primarily excited in the innermost part of the optical broad line region (BLR), or X-ray BLR. Alternatively, a warp could provide the solid angle needed to enhance Fe K-alpha line emission from intermediate radii, and might resolve an apparent discrepancy in the inclination of the innermost and outer disk in NGC 4151. Both warps and the BLR may originate through radiation pressure, so these explanations may be linked. We discuss our results in detail, and consider the potential for future observations with Chandra, XARM, and ATHENA to measure black hole masses and to study the intermediate disk in AGN using narrow Fe K-alpha emission lines.

Read full document.

"On obtaining neutron-star mass and radius constraints from quiescent low-mass X-ray binaries in the Galactic plane", by A. Marino et al.

1806MarinoetalBy Alessio Marino (Università degli Studi di Palermo, Palermo, Italy)

Analysing spectra of quiescent Low Mass X-Ray Binaries (LMXBs) hosting Neutron Stars (NSs) is one of the main techniques for measuring the mass and/or the radius of NSs and, in turn, constrain the Equation of state of ultra-dense matter. However, the precision and the power of these constraints are heavily related to the quality of the spectra. Furthermore, several biases affect the results obtained with this method, in particular, the uncertainty in the distance, the possibility of missing the presence of a power-law component in the spectrum and the evidence that a small variation in the energy range over which the spectrum is extracted might change significantly the results of the fits. As shown in this paper, these biases and limitations could be partially overcome with ESA's Athena mission.

We simulated spectra of two LMXBs hosting Neutron Stars, 4U 1608-52 and EXO 0748-676, based on Chandra archival observations and compared the simulated with the “original” spectra. In the case of 4U 1608-52, while the quality of the Chandra spectrum is too poor to give valuable constraints on the mass and/or the radius of the NS, a fit with a composite quasi-thermal plus power-law model performed on the simulated Athena spectrum results in precise outcomes (relative errors of 0,01-0,001%). On the other hand, the Chandra spectral analysis of EXO 0748-676 is not only limited by the statistics, but also by the energy range dependence, which is apparent analysing a 0.3-10 keV and a 0.5-10 keV spectrum; a simulated single Athena spectrum of the source is, on the contrary, unaffected by the change in the energy range. These results show how in the Athena era the search for constraints on the equation of state of ultra-dense matter via NS radius and mass measurements might receive a considerable boost, although without precise distance measurements an uncertainty associated with the range of plausible distances of the source must be taken into account.

Read full document.

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Advanced Telescope for High Energy Astrophysics


Athena (Advanced Telescope for High ENergy Astrophysics) is the X-ray observatory mission selected by ESA, within its Cosmic Vision programme, to address the Hot and Energetic Universe scientific theme. It is the second L(large)-class mission within that programme and is due for launch in early 2030s.

Athena will study how hot baryons assemble into groups and clusters of galaxies, determine their chemical enrichment across cosmic time, measure their mechanical energy and characterise the missing baryons which are expected to reside in intergalactic filamentary structures. At the same time, it will study the physics of accretion into compact objects, find the earliest accreting supermassive black holes and trace their growth even when in very obscured environment, and show how they influence the evolution of galaxies and clusters through feedback processes. Athena will also have a fast target of opportunity observational capability, enabling studies and usage of GRBs and other transient phenomena. As an observatory, Athena will offer vital information on high-energy phenomena on all classes of astrophysical objects, from solar system bodies to the most distant objects known. See Science chapter for more details.

Athena will consist of a single large-aperture grazing-incidence X-ray telescope, utilizing a novel technology (High-performance Si pore optics) developed in Europe, with 12m focal length and 5 arcsec HEW on-axis angular resolution. The focal plane contains two instruments. One is the Wide Field Imager (WFI) providing sensitive wide field imaging and spectroscopy and high count-rate capability. The other one is the X-ray Integral Field Unit (X-IFU) delivering spatially resolved high-resolution X-ray spectroscopy over a limited field of view. See Mission chapter for more details.

With its unparalleled capabilities, Athena will be a truly transformational observatory, operating in conjunction with other large observatories across the electromagnetic spectrum available in the early 2030s (like ALMA, ELT, JWST, SKA, CTA, etc).