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  • 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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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).