A new method to unveil blazars among multi-wavelength counterparts of Unassociated Fermi gamma-ray Sources

We discuss a new method for unveiling the possible blazar AGN nature among the numerous population of Unassociated Gamma-ray sources (UGS) in the Fermi catalogues. Our tool relies on positional correspondence of the Fermi object with X-ray sources (mostly from Swift-XRT), correlated with other radio, IR and optical data in the field. We built a set of Spectral Energy Distributions (SED) templates representative of the various blazar classes, and we quantitatively compared them to the observed multi-wavelength flux density data for all Swift-XRT sources found within the Fermi error-box, by taking advantage of some well-recognised regularities in the broad-band spectral properties of the objects. We tested the procedure by comparison with a few well-known blazars, and tested the chance for false positive recognition of UGS sources against known pulsars and other Galactic and extragalactic sources. Based on our spectral recognition tool, we find the blazar candidate counterparts for 14 2FGL UGSs among 183 selected at high galactic latitudes. Further our tool also allows us rough estimates of the redshift for the candidate blazar. In a few cases in which this has been possible (i.e. when the counterpart was a SDSS object), we verified that our estimate is consistent with the measured redshift. The estimated redshifts of the proposed UGS counterparts are larger, on average, than those of known Fermi blazars, a fact that might explain the lack of previous association or identification in published catalogues.Comment: 41 pages, 40 figures, 3 tables, accepted for publication in MNRA

Spectroscopy of 10 gamma-ray BL Lac objects at high redshift

We present high S/N optical spectra of 10 BL Lac objects detected at GeV energies by Fermi satellite (3FGL catalog), for which previous observations suggested that they are at relatively high redshift. The new observations, obtained at the 10 m Gran Telescopio Canarias, allowed us to find the redshift for J0814.5+2943 (z = 0.703) and we can set spectroscopic lower limit for J0008.0+4713 (z>1.659) and J1107.7+0222 (z>1.0735) on the basis of Mg II intervening absorption features. In addition we confirm the redshifts for J0505.5+0416 (z=0.423) and for J1450+5200 (z>2.470). Finally we contradict the previous z estimates for five objects (J0049.7+0237, J0243.5+7119, J0802.0+1005, J1109.4+2411, and J2116.1+3339).Comment: 10 pages, 2 figures, 4 tables; accepted for publication in Ap

On the redshift of the very high energy {\gamma}-ray BL Lac object S2 0109+22

The determination of the redshift of extragalactic gamma ray sources is of fundamental importance for the interpretation of their emission models and extragalactic population studies, AGN classification schemes, and to study the interaction with the extragalactic background light. Here we focus on the BL Lac S2 0109+22, recently detected at very high energies. We obtained a high signal-to-noise optical spectrum at Gran Telescopio Canarias for the source over the spectral range 4000-10000 Angstrom, to search for spectral features of the host galaxy and/or of the nuclear source and it was compared with previous observations in order to confirm and/or dispute its redshift determination. We find the S2 0109+22 optical spectrum is well represented by a power law continuum without any absorption or emission feature of Equivalent Width >0.1 Angstrom. Based on the new optical spectrum we are able to set a redshift lower limit z>0.35, assuming the source is hosted by a massive elliptical galaxy typical for this class of sources. The redshift z=0.265 proposed in the literature for this object is most probably referred to a r=18.3 galaxy at 15" from S2 0109. This galaxy could belong to a group of faint galaxies located at z~0.26.Comment: 5 pages, 5 figures; accepted on MNRA

A Multi-wavelength Study of Unidentified Objects in the Second Fermi Gamma-Ray Catalogue

The research field of the gamma-ray astronomy is new and rapidly grown, providing remarkable and promising scientific results. In the last decades, the development of new gamma-ray detectors on board satellites as the AGILE and the Fermi observatories, or groud-based instruments as the Imaging Atmospheric Cherenkov Technique telescope MAGIC, lead up to a big increase in the number of discovered gamma-ray emitters. Different types of astrophysical sources have been identified as gamma-ray emitter classes, of Galactic and extragalactic origin, such as Supernova Remants, Pulsars, Microquasars and Active Galactic Nuclei. Moreover, it has been suggested that gamma-ray radiation can be also related to annihilation/decay processes of Dark Matter particles expected in several celestial objects with high DM density as the Galactic Center, the Galaxy clusters, the Dwarf Spheroidal Satellite Galaxies of the Milky Way and finally the clumps of DM overdensities within the DM halo of our Galaxy. The aim of this PhD Thesis is both searching for gamma-ray signals from DM particles and combining the time-progressive all-sky Fermi survey with dedicated pointed observations performed by the Cherenkov telescopes. To perform this purpose, this Thesis work followed two different, but deeply related paths. The first part of this Thesis has adopted the Second Catalogue of the Fermi Gamma Ray Observatory (2FGL) as the main dataset for searches of new classes of extragalactic sources, DM objects candidates or unexpected high-energy phenomena. The Fermi mission has carried out a survey of the all sky at the gamma-ray energies from 30 MeV to 100 GeV, making use of the large area and field of view of the LAT instrument. In the 2FGL catalogue, 1873 points sources are detected: 1297 have been associated as known class of gamma-ray emitters, while the remaining 576 objects, the so-called Unassociated Fermi Objects (UFO), still lack a plausible identification and offer the best chance to search for DM sources. The population of the UFOs is the second major component of the gamma-ray sky and we selected a sub-sample of 183 UFOs of high Galactic latitude with |b|>20° (avoiding the confusion effects in the Galactic plane) with the aim to classify these sources and to determine if, among them, there are new types of AGNs, DM object candidates or unexpected high-energy phenomena. For each UFO of our sample we search for counterparts in optical, X-ray and radio band, in order to determine a possible association with a suitable set of sources of other astronomical catalogs. Then, through new tools based on multiwavelength approaches, we suggest a rather secure classification for most of them. Our UFO association procedure is primarily based on the use of available X-ray Swift satellite data that cover the FERMI error-box (typically of a few arcmins) associated to the gamma-ray detection. If an X-ray bright source is revealed within the FERMI error-box and if other sources at different wavelengths (from radio, IR and optical catalogues) are positionally coincident with the X-ray counterpart, we consider them as an unique source associated to the UFO. In addition we perform a dedicated X-ray data analysis for the X-ray counterpart found in order to determine the spectral shape in this energy band. Finally we build the UFO broad-band Spectral Energy Distribution (SED) combining the available measured fluxes at different wavelengths recovered as explained before. At this point, we perform the characterization of the SED of each our UFO, identifying it as belonging to a class of the main gamma-ray emitters. In particular for the blazar identification tool, we build a code based on the use of a library of bona-fide multi-frequency SED templates of known objects belonging to the four blazar categories: High-peaked (HBL), Intermediate-peaked (IBL), Low-peaked BL Lac (LBL), and Flat Spectrum radio Quasar (FSQR). Therefore, through the adoption of these SED template and choosing the one that models the data maximizing the likelihood, this code determines if a given UFO of our sample can be identified as a blazar object. In the same time, it provides an estimate of the redshift, still in the absence of spectroscopic observations (that is a well known issue for this kind of sources). From this procedure we obtain a reasonable classification as blazar objects for about 50 UFOs of our sample, belonging to all of the classes and with redshifts spanning from 0.2 to 1.5. This tool has been also applied on two well-known blazars, 1ES 1011+496 and PG 1553+113, used as test sources to prove the efficacy in recognizing AGN sources. Notably, we found results compatible with the real blazar class and redshift of the two test sources. Although in this PhD thesis we study UFOs of high Galactic latitude, the other category of gamma-ray emitters that we decided to consider as possible identification was also the class of microquasars. We have been encouraged to pursue this task because, during the procedure of association for some UFOs, we find set of MWL counterparts resulting in a peculiar broad-band SED similar to the those typically observed for microquasar objects. To achieve this interpretation, we built a diagnostic plot superimposing the luminosity data points of four known microquasars. If the SED points of a given UFO are located inside the regions defined by the known microquasar points, we suggest a microquasar identification for the studied object. About 15 UFOs of our sample are turned out to likely be Galactic sources, as microquasars, high galactic latitude Neutron Stars and pulsars. This could be a finding of great interest, given the small number of such objects in the 2FGL catalogue. For this reason, further investigations are ongoing. We note that for ten objects no X-ray sources in the available Swift/XRT data has been found within the Fermi error-box and, although we highlight that it might be dependent on the quality of the X-ray observations, they could be considered as the best candidates to perform DM searches. Finally, for the remaining UFOs, we cannot provide a clear identification since we found multiple sets of associations. Further observations, especially in the X-ray and radio bands, will allow us to disentangle this issue. The second line of investigation of this Thesis is in the field of very high energy (VHE) observations of Fermi sources with Cherenkov telescopes on ground, in particular with the MAGIC telescope, one of the largest IACT stereo systems and situated on the Canarian island La Palma, at 2245 m a.s.l. Such VHE data offer an invaluable astrophysical information on the sources. In this Thesis a detailed data analysis of the VHE radiation emitted by two HBL blazars, PG 1553+113 and 1ES 1011+496, is provided. Both sources have been observed in stereoscopic mode with MAGIC for a total of 12 hours and 21 hours, respectively, in order to perform a complete temporal evolution analysis of the integral flux and a detailed study of the VHE differential energy spectrum. Futhermore, the MAGIC observations were performed in the framework of dedicated multiwavelength campaigns, and for PG 1553+113 the campaign was planned in collaboration with the WEBT team involving several instruments of the north hemisphere operating at different energy bands. Simultaneous data, with a good temporal coverage, were collected from radio to VHE regimes, allowing us to sample the whole broad-band SED. The typical doubled bump shape, due to syncrothron and IC mechanisms, is showed by both sources, in agreement with the current Synchrotron Self-Compton blazar models. In addition both sources provide a modest (or any) activity in the HE, VHE and radio bands, while a clear variability in the UV and Optical regimes, related to the synchrotron bump frequencies, is present, especially for PG 1553+113. However any evidence of flare episodes have been detected. For this reasons, and thanks to high quality multiwavelength sampling of their SEDs, PG 1553+113 and 1ES 1011+496 were used as test sources to verify the efficency of our blazar identification tool (explained before) in recognizing AGN sources

The redshift of the BL Lac object TXS 0506+056

The bright BL Lac object TXS 0506+056 is a most likely counterpart of the IceCube neutrino event EHE 170922A. The lack of this redshift prevents a comprehensive understanding of the modeling of the source. We present high signal-to-noise optical spectroscopy, in the range 4100-9000 $\textrm{\AA}$, obtained at the 10.4m Gran Telescopio Canarias. The spectrum is characterized by a power law continuum and is marked by faint interstellar features. In the regions unaffected by these features, we found three very weak (EW $\sim$ 0.1 $\textrm{\AA}$) emission lines that we identify with [O II] 3727 $\textrm{\AA}$, [O III] 5007 $\textrm{\AA}$, and [N II] 6583 $\textrm{\AA}$, yielding the redshift z = 0.3365$\pm$0.0010.Comment: 7 pages, 3 figures, 2 tables; accepted for publication in ApJ

An Optical View of Extragalactic γ-Ray Emitters

The Fermi Gamma-ray Observatory discovered about a thousand extragalactic sources emitting energy from 100 MeV to 100 GeV. The majority of these sources belong to the class of blazars characterized by a quasi-featureless optical spectrum (BL Lac Objects). This hampers the determination of their redshift and therefore hinders the characterization of this class of objects. To investigate the nature of these sources and to determine their redshift, we are carrying out an extensive campaign using the 10 m Gran Telescopio Canarias to obtain high S/N ratio optical spectra. These observations allow us to confirm the blazar nature of the targets, to find new redshifts or to set stringent limits on the redshift based on the minimum equivalent width of specific absorption features that can be measured in the spectrum and are expected from their host galaxy, assuming it is a massive elliptical galaxy. These results are of importance for the multi-frequencies emission models of the blazars, to test their extreme physics, to shed light on their cosmic evolution and abundance in the far Universe. These gamma emitters are also of great importance for the characterization of the extragalactic background light through the absorption by the IR-optical background photons

Crizotinib-induced antitumour activity in human alveolar rhabdomyosarcoma cells is not solely dependent on ALK and MET inhibition

BACKGROUND: Rhabdomyosarcoma (RMS) is the most commonly diagnosed malignant soft tissue tumour in children and adolescents. Aberrant expression of Anaplastic Lymphoma Kinase (ALK) and MET gene has been implicated in the malignant progression of RMS, especially in the alveolar subtype. This observation suggests that crizotinib (PF-02341066), a kinase inhibitor against ALK and MET, may have a therapeutic role in RMS, although its antitumour activity in this malignancy has not yet been studied. METHODS: RH4 and RH30 alveolar RMS (ARMS) cell lines were treated with crizotinib and then assessed by using proliferation, viability, migration and colony formation assays. Multiple approaches, including flow cytometry, immunofluorescence, western blotting and siRNA-based knock-down, were used in order to investigate possible molecular mechanisms linked to crizotinib activity. RESULTS: In vitro treatment with crizotinib inhibited ALK and MET proteins, as well as Insulin-like Growth Factor 1 Receptor (IGF1R), with a concomitant robust dephosphorylation of AKT and ERK, two downstream kinases involved in RMS cell proliferation and survival. Exposure to crizotinib impaired cell growth, and accumulation at G2/M phase was attributed to an altered expression and activation of checkpoint regulators, such as Cyclin B1 and Cdc2. Crizotinib was able to induce apoptosis and autophagy in a dose-dependent manner, as shown by caspase-3 activation/PARP proteolytic cleavage down-regulation and by LC3 activation/p62 down-regulation, respectively. The accumulation of reactive oxygen species (ROS) seemed to contribute to crizotinib effects in RH4 and RH30 cells. Moreover, crizotinib-treated RH4 and RH30 cells exhibited a decreased migratory/invasive capacity and clonogenic potential. CONCLUSIONS: These results provide a further insight into the molecular mechanisms affected by crizotinib in ARMS cells inferring that it could be a useful therapeutic tool in ARMS cancer treatment