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Dec 06, 2017

DAMPE direct detection of a TeV-energy break in cosmic-ray spectrum of electrons and positrons

The Chinese Dark Matter Particle Explorer (DAMPE, also known as Sun Wukong) space mission published its first relevant scientific results in Nature scientific journal, presenting the precise measurement of high energy cosmic ray electrons plus positrons (CREs), and highlighting a solid break (i.e. a sharp variation) in the spectral energy distribution at about 0.9 TeV.

High energy CREs provide an ideal probe of sources in our neighbourhood since they loose quickly their energy during their propagation in the interstellar medium: precision measurement of their flux by DAMPE can considerably narrow down the parameter space of different models - such as nearby pulsars, supernova remnants and/or candidates of particle dark matter - needed in order to explain the 'positron excess' observed by AMS up to about 500 GeV. Evidence for a spectral break in the TeV energy range has been previously provided by indirect measurements of H.E.S.S., although the results were qualified by sizeable systematic uncertainties. DAMPE CREs spectrum data are instead characterized by unprecedentedly energy resolution and low background. A smoothly broken power-law model rather than a single power-law model can properly fit the majority of the spectrum.

The DAMPE mission is funded by the strategic priority science and technology projects in space science of the Chinese Academy of Sciences (CAS). DAMPE, China's first astroparticle physics satellite, was launched from Jiuquan Satellite Launch Center into sun-synchronous orbit on Dec. 17th, 2015. At an altitude of about 500 km, DAMPE has been collecting data since a week after its launch. In its first 530 days of science operation through June 8 of this year, DAMPE has detected 1.5 million cosmic ray electrons and positrons above 25 GeV. DAMPE, with its 1900Kg of total weight (1400Kg for the scientific experiment), is expected to record more than 10 billion cosmic ray events over its useful life-projected to exceed five years given the current state of its instruments.
DAMPE is a collaboration of more than a hundred scientists, technicians and students at nine institutes in China, Switzerland and Italy, under the leadership of the Purple Mountain Observatory (PMO) of the CAS. Italy is involved with a group of about twenty scientists from the INFN sections of Perugia, Bari and Lecce and the Universities of Perugia, Bari and Salento. A key component of DAMPE is the silicon tracker, developed with the coordination of INFN-Perugia, based on the experience and skills acquired in the work done for other space experiments such as AMS-02 and Fermi-LAT. After the publication of the results about CREs, the Italian scientific group is working to measure the flux of protons and ions, and to study the detected high energy gamma-ray photons.

DAMPE is among the projects developed in the SSDC center: not only DAMPE data have been immediately available for download from the Cosmic Rays Data Base, but SSDC appears among the institutes in the Nature publication thanks to the contribute of D.D'Urso to the data handling in the Europe.

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Feb 06, 2017

Fermi Gamma-ray Space Telescope identified the farthest gamma-ray blazars.

The detection of high-redshift (z>3) blazars by the Fermi Large Area Telescope (LAT) is of great astrophysical importance as they are extreme objects whose energetics remain a mystery.More importantly, high-z blazars tend to host massive black holes and can be used to constrain the space density of heavy black holes in the early Universe. The first detection with the LAT of five gamma-ray emitting blazars beyond z=3.3, has been announced and presented at the American Physical Society meeting in Washington in January 2017, and a paper describing the results has been submitted to The Astrophysical Journal Letters.

Light from the most distant object, NVSS J151002+570243 (z=4.31), began its journey to us when the universe was 1.4 billion years old. These objects have steeply falling gamma-ray spectral energy distributions and, those that have been observed in X-rays, a very hard X-ray spectrum, both typical of powerful blazars.Their Compton dominance (ratio of the inverse Compton to synchrotron peak luminosities) is also very large (> 20). All of these properties place these objects among the most extreme members of the blazar population. The radio-loudness may play a key role in rapid black hole growth in the early Universe. Fermi LAT could have detected just the tip of the iceberg, the first examples of a galaxy population that previously has not been detected in gamma rays

This research was led by researchers at the Clemson University, South Carolina, USA and at the ASI Space Science Data Center (SSDC), Rome, Italy, including D. Gasparrini (ASI SSDC and INFN). They began by searching for the most distant sources in a catalog of 1.4 million quasars, a galaxy class closely related to blazars. Because only the brightest sources can be detected at great cosmic distances, they then eliminated all but the brightest objects at radio wavelengths from the list. With a final sample of about 1,100 objects, the scientists then examined LAT data for all of them, resulting in the detection of five new gamma-ray blazars.

More details in the NASA's press release, ASI news, and in the forthcoming ApJ Letter.

Dec 30, 2016

50000 orbits of AGILE celebrated with the observation of an exceptional gamma-ray event

A few months before its tenth birthday in orbit, on December 19, 2016 at 06:08:53 UTC the AGILE satellite has reached the significant milestone of 50000 passes over the ASI Malindi Ground Station in Kenya with all detectors operating nominally.

AGILE is devoted to gamma-ray astrophysics, and it is also capable of detecting high energy phenomena of terrestrial nature, such as Terrestrial Gamma-ray Flashes (TGFs) revealed in the Earth equatorial regions. It is also currently at the forefront in the hunt for electromagnetic counterparts of gravitational waves.

The Italian satellite, launched on April 23, 2007 in low Earth orbit, is a small Scientific Mission of ASI, built and operated in cooperation with INAF, INFN, CIFS and with the participation of the Italian companies CGS, Thales-Alenia Space e Telespazio.

The small high-tech jewel, designed for an operative life of only two years, continues its mission with high efficiency, and it has celebrated its 50000 orbit with the observation of an exceptional gamma-ray event of extragalactic origin.



Credits: Screenshot downloaded on December 19, 2016 from the AGILEScience free app dedicated to the AGILE satellite.

As you can see from the fascinating image above, two monsters black holes at the center of the two distant active galactic nuclei CTA 102 and 3C 454.3, apparently close to each other in the AGILE sky map, made a spectacular double super-flare almost simultaneously in gamma rays.

The image was downloaded from the AGILEScience free app that enables anyone to follow in real time the latest satellite observations.

In particular, the CTA 102 source in these days was the brightest of the entire gamma-ray sky, even brighter than much closer sources within our galaxy, such as the Vela pulsar.

For more information, see also:
ASI news and INAF news (in Italian)
AGILE ATel #9743, ATel #9788, ATel #9840, ATel #9911 and references therein.

The AGILE data acquired from the ASI Malindi Ground Station are readily processed archived and managed by the SSDC/ASDC, the multi-mission ASI data center, and distributed to the PI Team alert system at INAF Bologna. The automatic alerts are analyzed daily by researchers of the AGILE team at several INAF institutes and at the ASDC itself.