Dario Gasparrini

A Minimal Spanning Tree algorithm for source detection in γ-ray images

We developed a source detection algorithm based on the Minimal Spanning Tree (MST), that is a graph-theoretical method useful for finding clusters in a given set of points. This algorithm is applied to gamma-ray bidimensional images where the points correspond to the arrival direction of photons, and the possible sources are associated with the regions where they clusterize. Some filters to select these clusters and to reduce the spurious detections are introduced. An empirical study of the statistical properties of MST on random fields is carried in order to derive some criteria to estimate the best filter values. We introduce also two parameters useful to verify the goodness of candidate sources. To show how the MST algorithm works in the practice, we present an application to an EGRET observation of the Virgo field, at high galactic latitude and with a low and rather uniform background, in which several sources are detected.

The number counts, luminosity functions, and evolution of microwave-selected (WMAP) blazars and radio galaxies

We have carried out an extensive search to identify the counterparts of all the microwave foreground sources listed in the WMAP 3-year catalogue using literature and archival data. Our work has led to the identifi- cation of 309 WMAP sources, 98% of which are blazars, radio quasars or radio galaxies. Only 7 WMAP detections were identified with other types of cosmic sources (3 starburst galaxies and 4 planetary/LBN nebulae). At present, 15 objects ( 15 ◦ ) which is virtually completely identified (99%). The microwave band is ideally suited for blazar statistical studies since this is the part of the electromagnetic spectrum that is least affected by the superposition of spectral components of different origin, and therefore by selection effects. Using this data-set we have derived number counts, luminosity functions and cosmological evolution of blazars and radio galaxies at microwave frequencies. Our results are in good agreement with those found at radio (cm) frequencies. The 5 GHz bivariate blazar luminosity functions are similar to those derived from the DXRBS survey, which shows that this sample is representative of the blazar population at 41 GHz. Microwave selected broad-lined quasars are about six times more abundant than BL Lacs, a ratio that is similar to, or larger than, that seen at radio and gamma-ray frequencies, once spectral selection effects are taken into account. This strongly suggests that the mechanism responsible for the generation of gamma-rays is, at first order, the same in all blazar types, leaving little room for models (like external Compton radiation) that predict very different gamma-ray emission in broad-lined and lineless blazars. Our results confirm, and strengthen on a more solid statistical base, the findings of Giommi & Colafrancesco (2004, 2006) that blazars and radio galaxies are the largest contaminants of the CMB anisotropy maps. We predict that these sources are also bright gamma-ray sources, most of which will be detected by the AGILE and Fermi satellites.

Challenges in reconciling observations and theory of the brightest high-energy flare ever of 3C 279

Recent high-energy missions have allowed keeping watch over blazars in flaring states, which provide deep insights into the engine powered by supermassive black holes. However, having a quasar caught in a very bright flaring state is not easy requiring long surveys. Therefore, the observation of such flaring events represents a goldmine for theoretical studies. Such a flaring event was captured by the INTEGRAL mission in June 2015 while performing its (as of today) deepest extragalactic survey when it caught the prominent blazar 3C~279 in its brightest flare ever recorded at gamma-ray energies. The flare was simultaneously recorded by the Fermi gamma-ray mission, by the Swift mission, by the INTEGRAL mission and by observations ranging from UV, through optical to the near-IR bands. The derived snapshot of this broad spectral energy distribution of the flare has been modeled in the context of a one-zone radiation transfer leptonic and lepto-hadronic models constraining the single emission components. The derived parameters of both models challenge the physical conditions in the jet. However, very recently published very-high-energy (VHE) data at TeV energies are very close to our lepto-hadronic model.

The 3rd Catalog of AGN Detected by the Fermi LAT

The third catalog of active galactic nuclei (AGNs) detected by the Fermi Large Area Telescope (3LAC) is presented. It is based on the third catalog (3FGL,cite{3FGL}) of sources detected with a test statistic greater than 25, using the first 4 years of data. The 3LAC includes 1591 AGNs located at high (

On the underlying particles in the jet of 3C 279

|b|>10^circ

Gamma-ray Beacons at the Dawn of the Universe

) Galactic latitudes (with 28 duplicate associations, thus corresponding to 1563 gamma-ray sources among 2192 sources in the 3FGL catalog), providing

Multiwavelength Picture of the Blazar S5 0716+714 during Its Brightest Outburst

71%

The Second LAT AGN Catalogue from the Fermi observatory

more sources with respect to the 2FGL. Various properties, such as gamma-ray fluxes and photon power law spectral indices, redshifts, gamma-ray luminosities, variability, and their correlations are presented and discussed for the different blazar and non-blazar classes.

Microwave to gamma-ray properties of Fermi-LAT detected AGNs

Recent high-energy missions have allowed keeping watch over blazars in flaring states, which provide deep insights into the engine powered by supermassive black holes. However, having a blazar caught in a very bright flaring state is not easy requiring long surveys. Therefore, the observation of such flaring events represents a goldmine for theoretical studies. nSuch a flaring event was captured by the INTEGRAL mission in June 2015 while performing its today’s deepest extragalactic survey when it caught the prominent blazar 3C 279 in its brightest flare ever recorded at gamma rays. The flare was simultaneously recorded by the Fermi-LAT mission, by the Swift mission, by the INTEGRAL mission and by observations ranging from UV, through optical to the near-IR bands. The derived snapshot of this broad spectral energy distribution of the flare has been modeled in the context of a one-zone radiation transfer leptonic and lepto-hadronic models constraining the single emission components. We discuss results and challenges faced by trying to reconcile these observations and theory. Also we show how the recently published VHE data from H.E.S.S. of the same flare tie in with our lepto-hadronic model.

A MST algorithm for source detection in γ‐ray images

Gamma ray detected high-redshift blazars (z>3) are intrinsically interesting since they inform us about the evolution of gamma-ray blazars and are, by definition, some of the more luminous blazars in the Universe. It has been found in many studies that such high z blazars host extremely massive black holes (