Accretion and ejection in black holes

The strong gravity of black holes may capture surrounding material that spirals around the black hole from the outer regions down to the event horizon. This material is heated to very high temperatures emitting radiation, mostly in the optical-UV and the X-ray frequencies of the electro-magnetic spectrum. A fraction of the inflowing material is sometimes ejected from the system in the form of winds or jets, ranging from low power to very powerful, highly collimated and sometimes highly relativistic jets. Our research activity is devoted to the understanding of the physical phenomena that regulates the accretion and ejection of material in black holes, by interpreting the radiative properties at multi-frequency, with a particular focus at X-gamma ray and radio emission.

Gamma ray burst (GRB), illustration. GRBs are focused beams of extremely high energy coming from distant galaxies. It is thought that they occur when a star is torn apart by powerful jets that form as it undergoes gravitational collapse. This massive short-lived burst of energy is hundreds of times brighter than an ordinary supernova or hypernova.


Transients and highly variable sources of various types are common in the Universe. Many of these objects have been discovered and extensively studied at different timescales ranging from less than 1 second to years. In recent times a wealth of new transients and associated phenomena have been discovered especially thanks to the all-sky or wide field instruments onboard Swift, Fermi, MAXI and INTEGRAL. These include e.g. bright Galactic black holes, NS sources, outbursts following tidal disruption events, gamma-ray bursts and supernova shock breakouts. Many new transients are expected to be discovered in the near future and new types will be amenable to study, like EM counterparts to GW sources discovered by LIGO/Virgo and possibly other multi-messenger sources as neutrino emitters, fast radio bursts etc.

epa05154649 A undated handout graphic, made available 11 February 2016 by NASA /  CALTECH-JPL, showing an artist's impression of gravitational waves generated by binary neutron stars. US researchers said 11 February 2016 they have detected gravitational waves, which physicist Albert Einstein first described 100 years ago as 'ripples in the fabric of space-time.' Scientists from Caltech and the Massachusetts Institute of Technology (MIT) made the announcement in Washington and other locations around the world. There were immediate suggestions that the discovery could well win them the Nobel Prize in Physics. The signal detected with LIGO, an observatory with sites on both sides of the United States, was very clear and there was no room for doubt that it was direct evidence of the waves, said Bruce Allen, who is acting director at Germany's Max Planck Institute for Gravitational Physics. He said two scientists with his group in the northern German city of Hanover were the first to notice the effect. The announcement may confirm Albert Einstein's last unproven theory, dating from 1916.  EPA/R. HURT / CALTECH-JPL / HANDOUT  HANDOUT EDITORIAL USE ONLY

Gravitational Waves

Gravitational waves (GW) were predicted nearly one hundred years ago as a natural consequence of general relativity and finally detected on 2015 September 14 by the LIGO-VIRGO Collaboration from the BBH (Binary Black Hole) merger GW150914. Since then INTEGRAL has observed in gamma rays 5 out of the 6 BBH GW detections mergers and provided the tightest upper limits on GW150914. In the last two years INTEGRAL has gained a leadership in the search of GW EM counterparts from binary black holes mergers, and detected the first gamma-ray counterpart, contemporary with Fermi, from two the coalescent neutron stars GW170817, starting the era of the “multi-messenger” astronomy: a success of our Group expected to continue in the future. The first detection of the prompt electromagnetic counterpart coincident with GW170817 has been a forward step in our knowledge of NS-NS merging.
An unexpected result was the extremely low isotropic luminosity of the event relative to other short gamma-ray bursts (SGRBs) with known redshifts, revealing a population of low luminosity SGRBs. The most popular interpretation is that GRB 170817A was viewed off-axis, rather than that the event had an intrinsically low luminosity. In either case, this result has spurred off-line searches for SGRBs below instrument trigger thresholds in hopes of finding similar events.



The latest IBIS survey by our team collected data from 1000 INTEGRAL orbits and resulted in a list of about 1000 hard -X ray Astrophysical emitting object of all types. A step forward is on the way to get 1500 orbit light curves in different energy bands and spectra covering the 20-300 keV range for these 1000 objects and many others from other surveys. This activity would lead to understanding of the hard X-ray properties of different classes, studying the variability patterns as well as modulation on long term with this data base covering almost 15 years. We will search for short term variability aiming to discover other SFXT candidates and possibly discovery new “exotic" objects. Also, a correlation between the Fermi unidentified objects and the H.E.S.S. galactic plane survey will be possible.