It’s official, AGILE works perfectly. Sent into orbit just three weeks ago, the small Italian satellite for the study of the violent Universe has already «captured», in the initial test phase of the instrumentation, its first gamma photon, which carries with it the information of an immense and remote cosmic explosion.
In the beginning of the afternoon of Tuesday May 8th, or to be precise at 15:19:32 Italian time, the satellite of the Italian Space Agency AGILE has begun its hunt for gamma rays. In fact, AGILE was built by the INFN Trieste division with the data acquisition designed by INAF. By opening its silicon eye for the first time, it has intercepted its first photon: a very high energy photon (about 250 MeV, mega-electron-volts), originated in a remote part of the Universe, probably outside our Galaxy. The first to notice, by analysing the data file just received by the ASI reception station of Malindi, in Kenya, were some young researchers of the INAF-IASF in Milan.
«Knowing that that file might hold the first photons », remembers Marco Tavani, from the INAF-IASF in Rome, scientific coordinator for AGILE, «we immediately started to look for them. And as soon as we detected one, I sent an email to the whole group. At that point it was already evening, but we were too excited: one by one I called all the researchers involved in the analysis, scattered between Milan, Rome and Bologna, to congratulate them». Since then, AGILE has been detecting thousands of gamma photons, just like we expected. When, following its orbit, it passes over Kenya, which happens 14 times a day, it sends down all its data to the ASI station in Malindi. From there the data is bounced back, through another satellite, to the Operational Mission Centre in Fucino, and finally to a data archive, from which researchers can download and analyze it.
“We have had to overcome many difficulties to miniaturize and bring the silicon detectors to work with much lower current levels than the ones normally used, but the INFN group in Trieste, under the direction of Michela Prest, has realized one measurement instrument which is really unique in its kind, which allows AGILE to measure, for the first time, both Gamma and X radiation together” declares Guido Barbiellini with satisfaction, AGILE scientific coordinator for the INFN. The efficiency of rejection of the particle noise (around 1000 to 1 was the noise-photons ratio) was crucial for success. It was designed by our group coordinated by Andrea Argan e realized by the Alcatel-Alenia Spazio of Milan.
The first photon intercepted by AGILE had travelled for billions of years, before ending its trip in the satellite’s silicon tracer: a kind of multilayer sandwich, where the photon, meeting heavy tungsten nuclei, has converted its energy in matter and anti-matter, giving rise to two particles: an electron and a positron. «For a few moments, the two particles travel together», explains Tavani, «but then, meeting other tungsten nuclei in the following layers, they separate, tracing a characteristic path shaped like a reversed Y ». For researchers this is the unmistakeable sign that the photon is «a good one», one of the ones AGILE was designed for, which will allow them to give an explanation to a number of hitherto unresolved phenomena about the most violent and fascinating displays of the Universe, from black holes to the gamma ray beams.
AGILE, whose name is the acronym of Astro-rivelatore Gamma a Immagini Leggero (Light Astro-Gamma image detector), is a mission of the Italian Space Agency, designed by the National Institute for Astrophysics, by the National Institute for Nuclear Physics, by the National Council for Research and by many Italian university Institutes. Entirely realized in Italy by the scientific Institutes and by an industrial consortium (Carlo Gavazzi Space, Alcatel Alenia Space, Oerlikon Contraves, Telespazio), was launched from India the last April 23rd. Its next objective is the finalization of the X detector (Super-Agile). Once this preliminary phase concluded, AGILE will observe a highly energetic pulsar, the Vela pulsar. Already by the end of June a map of this pulsar, both in gamma and in X rays, will be completed.
Great satisfaction among the Organisations that have promoted, funded and realized AGILE. For ASI "The fist signals from Agile confirm the importance of the mission and the role of our scientists in the high energy astrophysics. In the near future, along with Agile, ASI has the intention of promoting a chain of small missions, from Earth Observation to Telecommunications".
“The detection of the first gamma photon shows that AGILE works perfectly and it is an excellent result for Italy” - comments Sergio De Julio, Commissario Straordinario at INAF – “f the INAF Institutes in Rome, Milan and Bologna which have given an essential contribution to the development of AGILE and to the realization of its most innovative aspects, such as the simultaneous acquisition of Gamma and X rays. This is a unique characteristic which distinguishes it from all the other space missions, both the preceding ones in the X and Gamma fields, from NASA and ESA, and it will remain important in the near future too”.
“We are happy about this first manifestation of the AGILE apparatus, complementary to what another apparatus, PAMELA, has been realizing in orbit for about a year in its quest for antimatter.” – The president of INFN, Roberto Petronzio, also commented – “The first signal allows us to look with optimism to the next deadlines. The next deadline is for GLAST, the experiment that will be sent in orbit in February 2008 which will host 16 detection structures analogous to the ones on AGILE. Or like AMS which will enlarge Pamela’s search”.
For information: Marco Tavani, Marco.Tavani@iasf-roma.inaf.it, cell. 335 58 36 14