Examinando por Autor "Panessa, F."

Mostrando 1 - 3 de 3
  • No hay miniatura disponible
    Ítem
    An XMM-Newton look at the strongly variable radio-weak BL Lac Fermi J1544-0639
    (Astronomy and Astrophysics, 2019-02-01) Ursini, F.; Bassani, L.; Panessa, F.; Pian, E.; Bruni, G.; Bazzano, A.; Masetti, N.; Sokolovsky, K.; Ubertini, P.
    Context. Fermi J1544-0639/ASASSN-17gs/AT2017egv was identified as a gamma-ray/optical transient on May 15, 2017. Subsequent multiwavelength observations suggest that this source may belong to the new class of radio-weak BL Lacs. Aims. We studied the X-ray spectral properties and short-term variability of Fermi J1544-0639 to constrain the X-ray continuum emission mechanism of this peculiar source. Methods. We present the analysis of an XMM-Newton observation, 56 ks in length, performed on February 21, 2018. Results. The source exhibits strong X-ray variability, both in flux and spectral shape, on timescales of ∼10 ks, with a harder-when-brighter behaviour typical of BL Lacs. The X-ray spectrum is nicely described by a variable broken power law, with a break energy of around 2.7 keV consistent with radiative cooling due to Comptonization of broad-line region photons. We find evidence for a "soft excess", nicely described by a blackbody with a temperature of ∼0.2 keV, consistent with being produced by bulk Comptonization along the jet.
  • Miniatura
    Ítem
    Restarting activity in the nucleus of PBC J2333.9-2343 An extreme case of jet realignment
    (EDP Sciences, 2017-07) Hernández-García, L.; Panessa, F.; Giroletti, M.; Ghisellini, G.; Bassani, L.; Masetti, N.; Pović, M.; Bazzano, A.; Ubertini, P.; Malizia, A.; Chavushyan, V.
    Context. The giant radio galaxy PBC J2333.9-2343 shows different characteristics at different wavebands that are difficult to explain within the actual generic schemes of unification of active galactic nuclei (AGN). It is therefore a good candidate host for different phases of nuclear activity. Aims. We aim at disentangling the nature of this AGN by using simultaneous multiwavelength data. Methods. We obtained data in 2015 from the Very Long Baseline Array (VLBA), the San Pedro Mártir telescope, and the XMM-Newton observatories. This allows the study of the nuclear parts of the galaxy through its morphology and spectra and the analysis of the spectral energy distribution (SED). We also reanalysed previously-presented optical data from the San Pedro Mártir telescope from 2009 to provide a homogeneous comparison. Results. At X-ray frequencies the source is unabsorbed. The optical spectra are of a type 1.9 AGN, both in 2009 and 2015, although showing a broader component in 2015. The VLBA radio images show an inverted spectrum with a self-absorbed, optically thick compact core (αc = 0.40, where Sν ∝ ν+ α) and a steep-spectrum, optically thin jet (αj,8−15 = −0.5). The SED resembles that of typical blazars and is best represented by an external Compton (EC) model with a viewing angle of approximately 3–6°. The apparent size of the large-scale structure of PBC J2333.9-2343 must correspond to an intrinsic deprojected value of approximately 7 Mpc for θv < 10°, and to >13 Mpc for θv < 5°, a value much larger than the biggest giant radio galaxy known, which is 4.5 Mpc. Conclusions. The above arguments suggest that PBC J2333.9-2343 has undergone a new episode of nuclear activity and that the direction of the new jet has changed in the plane of the sky and is now pointing towards us. This changes this source from a radio galaxy to a blazar, a very exceptional case of restarting activity.
  • Miniatura
    Ítem
    Variable broad lines and outflow in the weak blazar PBC J2333.9-2343
    (Oxford University Press, 2018-08) Hernández-García, L.; Vietri, G.; Panessa, F.; Piconcelli, E.; Chavushyan, V.; Jiménez-Andrade, E.F.; Bassani, L.; Bazzano, A.; Cazzoli, S.; Malizia, A.; Masetti, N.; Monaco, L.; Pović, M.; Saviane, I.; Ubertini, P.
    PBC J2333.9-2343 is a peculiar active nucleus with two giant radio lobes and a weak blazarlike nucleus at their centre. In this work we show new optical, ultraviolet (UV), and X-ray data taken from the San Pedro Mártir telescope, the New Technology Telescope, NTT/EFOSC2, and the Swift/XRT satellite. The source is highly variable at all frequencies, in particular the strongest variations are found in the broad Hα component with a flux increase of 61±4 per cent between 2009 and 2016, following the X-ray flux increase of 62±6 per cent between 2010 and 2016. We also detected a broad Hβ component in 2016, making the optical classification change from type 1.9 to type 1.8 in 1 yr. We have also detected a broad component of the [OIII]λ5007 line, which is blue-shifted and of high velocity, suggesting an origin from a highly disturbed medium, possibly an outflow. The line flux variability and broad widths are indicative of a jet that is, at least in part, responsible for the ionization of the broad line region (BLR) and narrow line region (NLR). © 2018 The Author(s) Published by Oxford University Press on behalf of the Royal Astronomical Society.