At seven this morning, from Cape Canaveral, the launch of the IXPE satellite telescope took place, born from the collaboration between NASA and an Italian partnership under the coordination of ASI, the Italian space agency, and with the scientific contribution of the National Institute of Astrophysics. A fundamental role was played by a team of researchers from the INAF-Astronomical Observatory of Cagliari both in the technological development of on-board instruments and in the development of observational and scientific procedures. For the first time, the Sardinian Observatory is directly participating in an international space mission of this magnitude.

IXPE, acronym for Imaging X-ray Polarimetry Explorer, is the name given to the NASA mission that brought a new telescope into orbit aboard a Falcon-9 from the American company SpaceX. The fundamental novelty is the measurement of the polarization of X-rays coming from some types of highly energetic cosmic objects such as supermassive black holes at the center of galaxies (billions of times the mass of the Sun) or tiny and very heavy neutron stars (the mass of Sun in just 20 km in diameter).

Italy provided the "heart" of the scientific mission: the detectors capable of recognizing the polarization of the X-rays of celestial objects that the satellite will observe during its 3 years of expected nominal life. In total, the Italian team is close to one hundred people and of these thirty - including the scientific manager Paolo Soffitta - are Inaf personnel and, in particular, four represent the INAF team from Cagliari: Alessio Trois, Matteo Bachetti, Maura Pilia and Andrea Possenti.

Trois, researcher technologist from Cagliari trained in the space astrophysics institutes of Milan and Rome before moving to Cagliari, explains: "The delivery of the Ixpe instrument to American colleagues in such a short time, just 3 years, was a success made possible only thanks to to the extraordinary organizational synergy of all the institutions involved. As Inaf of Cagliari we have made a substantial contribution in defining the logic of the on-board computer, in the integration and testing of the instrument as well as in its physical integration on the satellite module that will take it into orbit and in the qualification campaign of the entire observatory, consisting of by three identical and independent telescopes. We also take care of the support for the instrument's in-flight operations which will be managed directly by the American industry. "

“The preparation of a space mission - he adds - requires spasmodic attention to detail. The costs for launching space telescopes are very high. Furthermore, with the sole exception of the Hubble telescope, no missions are set up to be visited and adjusted in orbit. Therefore, every transistor, every solder, every rivet must have a purpose and work perfectly. Everything must be validated, tested and verified before launch in order to be sure that the satellite will be able to survive the extreme conditions it will be subjected to from launch to its operation in orbit around the Earth, when exposed to gamma rays and extreme temperature excursions. . "

The instruments must therefore be tested and calibrated with painstaking care, and this requires months of work (for Ixpe about 12) in overprotected environments, the so-called "clean rooms". The analysis of all these preparations is carried out with a dedicated software that is specially written and which in turn must be thoroughly tested.

His writing is essential not only to validate the technical part of the assembly of the instruments but also to evaluate which observations will maximize the impact of the mission. To do this, INAF researcher Maura Pilia - originally from Villasalto and trained in Cagliari, Bologna, Milan and the Netherlands - worked extensively in the programming and simulation of scenarios and mathematical models to be applied to some of Ixpe's favorite celestial objects: the milliseconds pulsar. These are neutron stars that rotate (and consequently "pulsate") at incredible speeds: up to more than 700 rotations per second, which is why they are considered the cosmic clocks par excellence. The polarized X-ray signals that Ixpe will be able to observe will integrate the observations made in wavelengths other than X-rays. "These simulations - emphasizes Pilia - are not only fundamental for understanding which sources are optimal for observations with Ixpe and therefore establish observational priorities, but also allow us to arrive prepared for the actual observations, having already prepared the tools for data analysis and models for comparison. We expect many discoveries and we want to be able to communicate them fully and as soon as possible ".

The only way to get X-rays coming from Space is to send satellites into orbit and for Ixpe a fundamental role was played by Matteo Bachetti, a Selargius researcher with experience in France, in the United States and who has become one of the points of reference for temporal analyzes with the satellite, so much so that he won a medal awarded by NASA and an honor from the municipality where he was born. Today, he brings this experience to Ixpe: “For example, to process each X-ray captured by NuSTAR and Ixpe - he explains - the detector switches off for a very short time, a phenomenon called dead time. This creates problems in searching for periodic signals in data from very bright sources. Over time we have developed strategies to circumvent these problems in NuSTAR that will be useful for Ixpe ”.

Among the supporters of the involvement of the Sardinian research center in the project, there is the astrophysicist Andrea Possenti, first researcher and coordinator of the scientific activities of INAF-OAC connected with the mission: "After the thrill of the launch - he says - they will arrive soon There are also abundant scientific discoveries, for example in the field of magnetar stars, which are the most magnetized objects in the Universe. The observation in polarized X-rays will reveal the geometry of these magnetic fields one million billion times more intense than that of our Earth ".

The participation of the Astronomical Observatory of Cagliari in the Ixpe project was not accidental and represents a great achievement because it is the first time that INAF-OAC directly contributes to the preparation of an international space mission. “This result - it is underlined in a note - was made possible thanks to the far-sighted project of the Sardinia Radio Telescope (SRT) wanted and realized by the late president of INAF, Nichi D'Amico. The Sardinian radio telescope has in fact had a double role. On the one hand, it has allowed the return of numerous Italian researchers and technologists who worked outside Sardinia while attracting many researchers from every corner of the world (South Africa, China, Pakistan, Australia, United States, to name a few) and with they their knowledge of technology and science in various fields. Furthermore, the construction of SRT has strengthened the collaboration between the Italian Space Agency and INAF which share the same instrument on Sardinian soil, constantly improving it with mutual benefit ".

“It is a very exciting and satisfying moment for the Astronomical Observatory of Cagliari - concludes the director of INAF-OAC, Emilio Molinari - which has confirmed itself as a driving force of excellence for the whole territory. Able to offer employment opportunities for young female researchers and consequently to grow on the island of expertise of great value, able to play leading roles in world-class scientific enterprises ".

(Unioneonline / ss)

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