A new flaring high energy gamma-ray source

We report the detection of a new gamma-ray source in the Fermi-LAT sky using a source detection tool based on the Minimal Spanning Tree algorithm. The source, not reported in previous LAT catalogues but very recently observed in the X-rays and optical bands, is characterized by an increasing gamma-ray activity in 2012 June-September, reaching a weekly peak flux of (3.3+-0.6)*10^-7 photons cm^-2 s^-1. A search for a possible counterpart provides indication that it can be associated with the radio source NVSS J141828+354250 whose optical SDSS colours are typical of a blazar.Comment: 4 pages, 3 figures. Accepted for publication in Astronomy & Astrophysic

ECONOMIC ANALYSIS IN DISPUTES OVER TRADE REMEDY AND RELATED MEASURES IN AGRICULTURE, WITH EXAMPLES FROM RECENT CASES

International Relations/Trade,

Unidentifed gamma-ray sources: hunting gamma-ray blazars

One of the main scientific objectives of the ongoing Fermi mission is unveiling the nature of the unidentified gamma-ray sources (UGSs). Despite the large improvements of Fermi in the localization of gamma-ray sources with respect to the past gamma-ray missions, about one third of the Fermi-detected objects are still not associated to low energy counterparts. Recently, using the Wide-Field Infrared Survey Explorer (WISE) survey, we discovered that blazars, the rarest class of Active Galactic Nuclei and the largest population of gamma-ray sources, can be recognized and separated from other extragalactic sources on the basis of their infrared (IR) colors. Based on this result, we designed an association method for the gamma-ray sources to reognize if there is a blazar candidate within the positional uncertainty region of a generic gamma-ray source. With this new IR diagnostic tool, we searched for gamma-ray blazar candidates associated to the UGS sample of the second Fermi gamma-ray catalog (2FGL). We found that our method associates at least one gamma-ray blazar candidate as a counterpart each of 156 out of 313 UGSs analyzed. These new low-energy candidates have the same IR properties as the blazars associated to gamma-ray sources in the 2FGL catalog.Comment: 24 pages, 4 figures, Accepted for publication on the Astrophysical Journa

WATCAT: a tale of wide-angle tailed radio galaxies

We present a catalog of 47 wide-angle tailed radio galaxies (WATs), the WATCAT; these galaxies were selected by combining observations from the National Radio Astronomy Observatory/Very Large Array Sky Survey (NVSS), the Faint Images of the Radio Sky at Twenty-Centimeters (FIRST), and the Sloan Digital Sky Survey (SDSS), and mainly built including a radio morphological classification. We included in the catalog only radio sources showing two-sided jets with two clear "warmspots" (i.e., jet knots as bright as 20% of the nucleus) lying on the opposite side of the radio core, and having classical extended emission resembling a plume beyond them. The catalog is limited to redshifts z $\leq$ 0.15, and lists only sources with radio emission extended beyond 30 kpc from the host galaxy. We found that host galaxies of WATCAT sources are all luminous (-20.5 $\gtrsim$ Mr $\gtrsim$ -23.7), red early-type galaxies with black hole masses in the range $10^8\lesssim$ M$_{\rm BH} \lesssim 10^9$ M$_\odot$. The spectroscopic classification indicates that they are all low-excitation galaxies (LEGs). Comparing WAT multifrequency properties with those of FRI and FRII radio galaxies at the same redshifts, we conclude that WATs show multifrequency properties remarkably similar to FRI radio galaxies, having radio power of typical FRIIs

Deciphering the large-scale environment of radio galaxies in the local Universe: where do they born, grow and die?

The role played by the large-scale environment on the nuclear activity of radio galaxies (RGs), is still not completely understood. Accretion mode, jet power and galaxy evolution are connected with their large-scale environment from tens to hundreds of kpc. Here we present a detailed, statistical, analysis of the large-scale environment for two samples of RGs up to redshifts $z_\mathrm{src}$=0.15. The main advantages of our study, with respect to those already present in the literature, are due to the extremely homogeneous selection criteria of catalogs adopted to perform our investigation. This is also coupled with the use of several clustering algorithms. We performed a direct search of galaxy-rich environments around RGs using them as beacon. To perform this study we also developed a new method that does not appear to suffer by a strong $z_\mathrm{src}$ dependence as other algorithms. We conclude that, despite their radio morphological (FR\,I $vs$ FR\,II) and/or their optical (HERG $vs$ LERG) classification, RGs in the local Universe tend to live in galaxy-rich large-scale environments having similar characteristics and richness. We highlight that the fraction of FR\,Is-LERG, inhabiting galaxy rich environments, appears larger than that of FR\,IIs-LERG. We also found that 5 out of 7 FR\,II-HERGs, with $z_\mathrm{src}\leq$0.11, lie in groups/clusters of galaxies. However, we recognize that, despite the high level of completeness of our catalogs, when restricting to the local Universe, the low number of HERGs ($\sim$10\% of the total FR\,IIs investigated) prevent us to make a strong statistical conclusion about this source class.Comment: 21 pages, 25 figures, accepted for publication on the Astrophysical Journal Supplement Series - pre-proof versio

Early-type galaxies in the Chandra COSMOS Survey

We study a sample of 69 X-ray detected Early Type Galaxies (ETGs), selected from the Chandra COSMOS survey, to explore the relation between the X-ray luminosity of hot gaseous halos (L_X, gas) and the integrated stellar luminosity (L_K) of the galaxies, in a range of redshift extending out to z=1.5. In the local universe a tight steep relationship has been stablished between these two quantities (L_X,gas~ L_K^4.5) suggesting the presence of largely virialized halos in X-ray luminous systems. We use well established relations from the study of local universe ETGs, together with the expected evolution of the X-ray emission, to subtract the contribution of low mass X-ray binary populations (LMXBs) from the X-ray luminosity of our sample. Our selection minimizes the presence of active galactic nuclei (AGN), yielding a sample representative of normal passive COSMOS ETGs; therefore the resulting luminosity should be representative of gaseous halos, although we cannot exclude other sources such as obscured AGN, or enhanced X-ray emission connected with embedded star formation in the higher z galaxies. We find that most of the galaxies with estimated L_X<10^42 erg/s and z<0.55 follow the L_X,gas- L_K relation of local universe ETGs. For these galaxies, the gravitational mass can be estimated with a certain degree of confidence from the local virial relation. However, the more luminous (10^42<L_X<10^43.5 erg/s) and distant galaxies present significantly larger scatter; these galaxies also tend to have younger stellar ages. The divergence from the local L_X,gas - L_K relation in these galaxies implies significantly enhanced X-ray emission, up to a factor of 100 larger than predicted from the local relation. We discuss the implications of this result for the presence of hidden AGN, and the evolution of hot halos, in the presence of nuclear and star formation feedback.Comment: 29 pages, 10 figures, accepted for publication on ApJ on May 27 201

Unveiling the nature of the unidentified gamma-ray sources III: gamma-ray blazar-like counterparts at low radio frequencies

About one third of the gamma-ray sources listed in the second Fermi LAT catalog (2FGL) have no firmly established counterpart at lower energies so being classified as unidentified gamma-ray sources (UGSs). Here we propose a new approach to find candidate counterparts for the UGSs based on the 325 MHz radio survey performed with Westerbork Synthesis Radio Telescope (WSRT) in the northern hemisphere. First we investigate the low-frequency radio properties of blazars, the largest known population of gamma-ray sources; then we search for sources with similar radio properties combining the information derived from the Westerbork Northern Sky Survey (WENSS) with those of the NRAO VLA Sky survey (NVSS). We present a list of candidate counterparts for 32 UGSs with at least one counterpart in the WENSS. We also performed an extensive research in literature to look for infrared and optical counterparts of the gamma-ray blazar candidates selected with the low-frequency radio observations to confirm their nature. On the basis of our multifrequency research we identify 23 new gamma-ray blazar candidates out of 32 UGSs investigated. Comparison with previous results on the UGSs are also presented. Finally, we speculate on the advantages on the use of the low-frequency radio observations to associate UGSs and to search for gamma-ray pulsar candidates.Comment: 15 pages, 13 figures, 3 tables, ApJS accepted for publication (version pre-proof corrections

LOFAR observations of 4C+19.44. On the discovery of low frequency spectral curvature in relativistic jet knots

We present the first LOFAR observations of the radio jet in the quasar 4C+19.44 (a.k.a. PKS 1354+19) obtained with the long baselines. The achieved resolution is very well matched to that of archival Jansky Very Large Array (JVLA) observations at higher radio frequencies as well as the archival X-ray images obtained with {\it Chandra}. We found that, for several knots along the jet, the radio flux densities measured at hundreds of MHz lie well below the values estimated by extrapolating the GHz spectra. This clearly indicates the presence of spectral curvature. Radio spectral curvature has been already observed in different source classes and/or extended radio structures and it has been often interpreted as due to intrinsic processes, as a curved particle energy distribution, rather than absorption mechanisms ({ Razin-Tsytovich} effect, free-free or synchrotron self absorption to name a few). Here we discuss our results according to the scenario where particles undergo stochastic acceleration mechanisms also in quasar jet knots.Comment: 13 pages, 4 tables, 4 figures, pre-proof version, published on the Astrophysical Journal (Harris, et al. 2019 ApJ, 873, 21