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The Palermo Active GalactIc Nuclei Entity (PAGiNE)Active galactic nuclei (AGN) are astronomical objects characterized by very high luminosities (1042–1048 ergs/s ) concentrated in small volumes (<<1 pc3). This emission is extended over the whole electromagnetic spectrum, from the radio domain through X and gamma-rays. The most probable (and currently accepted) explanation is that the radiation is supported by accretion of matter onto a Super-Massive Black Hole (SMBH), and possibly also by the SMBH rotational energy (e.g. Urry & Padovani, 1995). AGN can be considered a natural laboratory for extreme physics conditions, which cannot be reproduced on Earth. Moreover, their high intrinsic luminosity makes them the most distant observable objects, of great importance for the study of large scale structures in cosmology. The PAGiNE is active in the studies of two classes of AGNs: Blazars
High-energy studies of blazarsGamma-ray blazarsAmong active galactic nuclei (AGNs), blazars show strong flux variability at almost all frequencies of their spectral energy distributions (SED). The Energetic Gamma Ray Experiment Telescope (EGRET) instrument on board the Compton Gamma-Ray Observatory (CGRO) detected, above 30 MeV, several AGNs, establishing the blazars as a class of gamma-ray sources (Hartman et al., 1999, ApJS, 123, 79). Gamma-ray blazars are characterized by high variability on different timescales. At energies above 30 MeV, variability has been detected on timescales from one day (e.g. PKS 1622-297; Zhang et al., 2002, A&A, 386, 843) to one month (e.g. PKS 0208-512; von Montigny et al., 1995, ApJ, 440, 525). Blazars emit across several decades of energy, from the radio to the TeV energy band, and thus, they are the perfect candidates for simultaneous observations at different wavelengths. Nevertheless, only a few objects were detected on a timescale of about two weeks in the gamma-ray energy band, and simultaneously monitored at different energies, obtaining a multi frequency coverage. AGILE flaring blazarsSince its launch on 2007 April 23, the AGILE satellite (Tavani et al, 2009, A&A, in press) detected several flaring blazars in the gamma-ray energy band (30 MeV - 30 GeV), and thanks to the fast quick-look analysis procedure, extensive multi wavelength campaigns were organized for many of them.
The following Table shows the AGILE flaring blazar sample. Up to now,
a few sources were detected more than once,
S5 0716+714, PKS 1510-089, and 3C 454.3.
Multiwavelength Campaigns
INAF-IASF Palermo is deeply involved into the multiwavelength studies
of gamma-ray blazars. Stefano Vercellone is a member of the AGILE Team and he is
currently the Chairman of the AGILE AGN Working Groups.
This first result allowed us to perform several other multiwavelength campaigns lead by AGILE and involving Swift. These campaigns were and are currently perfomed both by means of dedicated high priority Target of Opportunuties (ToOs), and by means of pre-approved Guest Investigator (GI) proposals (Prop. ID #04024, PI S. Vercellone; Prop. ID #5080033, PI S. Vercellone). In particular, successful campaigns were performed on PKS 1510-089, S5 0716+714, 3C 454.3, and PKS 0537-441. For all of these objects scientific papers are in preparations. Monitoring CampaignsSince March 2009, we started a Swift monitoring campaign on two interesting blazars, PKS 1553+113 and PKS 0537-441, which are often monitored at optical/IR frequencies. The main purpose of the Swift observations, which are performed once per month (currently approved thoughout Summer 2009) is to provide a constant, evenly-paced monitoring of the flux level of these two sources throughout the year. This activity is locally led at IASF-Palermo by Pat Romano and in Italy by E. Pian (OA-Trieste) and Filippo D'ammando (IASF-Roma). Swift Fill-in TargetsA Swift fill-in target project is currently on-going. The aim of this project, led by Boris Sbarufatti of the Swift Team, is to compare the X-ray properties of a sample of candidate gamma-ray emitters with those of known gamma-ray loud objects. ReferencesA list of accepted papers on high-energy blazars can be found at the following LINK.External linksThe most relevant links are:Contact person at IASF-Palermo:
Optical spectroscopy of BL Lacs
Among blazars, BL Lac objects are characterized by the absence or extreme weakness of the spectral features in the optical-near UV spectral range. This hampers the determination of their redshift (See Fig. 1). In the standard model of BL Lacs, the weak emission lines (if present) are generated by fluorescence, as in other types of AGN, but the line equivalent widths (EW) are reduced by the strong beamed continuum, caused by the alignment with our line of sight of the relativistic jet produced by the nucleus. On the other hand absorption lines can be produced either from spectral features of the stellar population of the host galaxy (suffering dilution from the jet emission as in the case of emission lines) or from intervening halos as in the case of quasars. Detectability of the absorption features depends inversely on the brightness state of the central source. Because of the weakness of the emission lines (usually EW~5 Å) and the relatively bright central continuum source with respect to the emission from the host galaxy, in many cases the redshift of these objects is unknown and/or very uncertain. The obvious implication of this is that the distance of the sources remains undetermined, hampering a proper evaluation the physical parameters of the objects.
Since 2003 we had an ongoing program of optical spectroscopy at the European Southern Observatory (ESO) 8-meter Very Large Telescope (VLT) which utilizes the telescope in service mode under non-optimal seeing conditions, aimed at obtaining the redshift of known BL Lacs selected from the literature(see Fig. 2). The high S/N ratio that can be reached using a 8 meter telescope allows us to detect spectral lines down to an EW limit of 0.1 Å for the brightest objects. Thus far, out of 35 observed BL Lacs, we were able to measure the redshift in 17 cases. For the remaining objects we developed a technique which, given an EW upper limit and under the assumption that BL Lac host galaxies are candles (Sbarufatti et al., 2005b), enables us to give a lower limit on the redshift of the objects (Sbarufatti et al., 2006a). The observations were concluded in March 2009, with the data analysis of the last year of observations still ongoing. Starting from April 2009, we began a new program of ESO-VLT optical spectroscopy of BL Lacs, aimed at the measurement of the redshift of targets selected from the Plotkin et al. 2008 list of SDSS/FIRST BL Lacs. This complete sample of objects has the advantage of having an extensive, homogeneous data coverage in the radio, optical and X-ray bands. Integrating the existing SDSS optical spectroscopy with higher S/N VLT spectra will allow us to better exploit this catalog. ReferencesA list of accepted papers on BL LAC optical spectroscopy can be found at the following LINK.External linksThe most relevant links are:ZBLLAC contact person at IASF-Palermo:
LINERSIn collaboration with E. Pian (OA Trieste), D. Maoz (Tel Aviv), A. Cucchiara and C. Pagani (PSU), we are performing an investigation of the X-ray and UV properties of four LINERs observed with Swift, aimed at constructing good S/N and strictly simultaneous UV-X-ray SEDs. In the current paradigm, LINER emission is dominated by geometrically thick, radiatively inefficient radiation flows (RIAFs) as opposed to radiatively efficient, geometrically thin accretion disks thought to power higher luminosity AGNs (Seyferts and QSOs). However, some recent studies have found more similarities than differences between the SEDs of LINERs and those of more luminous AGNs, suggesting that LINERs are powered by the same mechanisms active in higher luminosity AGNs. Our new observations allow us to test this idea.ReferencesA list of accepted papers on LINERs can be found at the following LINK.LINERs contact person at IASF-Palermo: Current PAGiNE Team members:
Contact person at IASF-Palermo:
Last Modification: Friday, February 3 2012 Edit by Pat Romano |
F. D'Ammando (@ Perugia)