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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.