{ital ASCA} and Contemporaneous Ground-based Observations of the BL Lacertae Objects 1749{plus}096 and 2200{plus}420 (BL {bold Lac})

Sambruna, R M; Ghisellini, G; Hooper, E; Kollgaard, R I; Pesce, J E; Urry, C M

doi:10.1086/307005

Title: {ital ASCA} and Contemporaneous Ground-based Observations of the BL Lacertae Objects 1749{plus}096 and 2200{plus}420 (BL {bold Lac})

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Abstract

We present {ital ASCA} observations of the radio-selected BL Lacertae objects 1749{plus}096 (z=0.32) and 2200{plus}420 (BL Lac, z=0.069) performed in 1995 September and November, respectively. The {ital ASCA} spectra of both sources can be described as a first approximation by a power law with photon index {Gamma}{approximately}2. This is flatter than for most X-ray{endash}selected BL Lacs observed with {ital ASCA}, in agreement with the predictions of current blazar unification models. While 1749{plus}096 exhibits tentative evidence for spectral flattening at low energies, a concave continuum is detected for 2200{plus}420: the steep low-energy component is consistent with the high-energy tail of the synchrotron emission responsible for the longer wavelengths, while the harder tail at higher energies is the onset of the Compton component. The two BL Lacs were observed with ground-based telescopes from radio to TeV energies contemporaneously with {ital ASCA}. The spectral energy distributions are consistent with synchrotron self-Compton emission from a single homogeneous region shortward of the IR/optical wavelengths, with a second component in the radio domain related to a more extended emission region. For 2200{plus}420, comparing the 1995 November state with the optical/GeV flare of 1997 July, we find that models requiring inverse Compton scattering of external photons providemore »« less

Authors:

Sambruna, R M ^[1]; Ghisellini, G ^[2]; Hooper, E ^[3]; Kollgaard, R I ^[4]; Pesce, J E ^[1]; Urry, C M ^[5]

Pennsylvania State University, Department of Astronomy and Astrophysics, 525 Davey Lab, State College, PA 16802 (United States)
Osservatorio Astronomico di Brera, via Bianchi 46, 22055 Merate (Saint Lucia) (Italy)
Harvard-Smithsonian Center for Astrophysics, 60 Garden Street, Cambridge, MA 02138 (United States)
Fermi National Accelerator Laboratory, Pine Road and Kirk Street, Batavia, IL 60510 (United States)
Space Telescope Science Institute, 3700 San Martin Drive, Baltimore, MD 21218 (United States)

Publication Date:: Thu Apr 01 00:00:00 EST 1999

OSTI Identifier:: 353755

Resource Type:: Journal Article

Journal Name:: Astrophysical Journal

Additional Journal Information:: Journal Volume: 515; Journal Issue: 1; Other Information: PBD: Apr 1999

Country of Publication:: United States

Language:: English

Subject:: 66 PHYSICS; PHOTOEMISSION; SYNCHROTRON RADIATION; SPECTRAL DENSITY; EMISSION SPECTRA; BL LACERTAE OBJECTS; GALAXIES; X-RAY GALAXIES; INDIVIDUAL (1749 + 096); INDIVIDUAL (2200 + 420)

Citation Formats


                    Sambruna, R M, Ghisellini, G, Hooper, E, Kollgaard, R I, Pesce, J E, and Urry, C M. {ital ASCA} and Contemporaneous Ground-based Observations of the BL Lacertae Objects 1749{plus}096 and 2200{plus}420 (BL {bold Lac}).  United States: N. p., 1999. 
        Web.  doi:10.1086/307005.

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                    Sambruna, R M, Ghisellini, G, Hooper, E, Kollgaard, R I, Pesce, J E, & Urry, C M. {ital ASCA} and Contemporaneous Ground-based Observations of the BL Lacertae Objects 1749{plus}096 and 2200{plus}420 (BL {bold Lac}).  United States.  https://doi.org/10.1086/307005

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                    Sambruna, R M, Ghisellini, G, Hooper, E, Kollgaard, R I, Pesce, J E, and Urry, C M. 1999.  
        "{ital ASCA} and Contemporaneous Ground-based Observations of the BL Lacertae Objects 1749{plus}096 and 2200{plus}420 (BL {bold Lac})".  United States.  https://doi.org/10.1086/307005.

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@article{osti_353755,

  title        = {{ital ASCA} and Contemporaneous Ground-based Observations of the BL Lacertae Objects 1749{plus}096 and 2200{plus}420 (BL {bold Lac})},

  author       = {Sambruna, R M and Ghisellini, G and Hooper, E and Kollgaard, R I and Pesce, J E and Urry, C M},

  abstractNote = {We present {ital ASCA} observations of the radio-selected BL Lacertae objects 1749{plus}096 (z=0.32) and 2200{plus}420 (BL Lac, z=0.069) performed in 1995 September and November, respectively. The {ital ASCA} spectra of both sources can be described as a first approximation by a power law with photon index {Gamma}{approximately}2. This is flatter than for most X-ray{endash}selected BL Lacs observed with {ital ASCA}, in agreement with the predictions of current blazar unification models. While 1749{plus}096 exhibits tentative evidence for spectral flattening at low energies, a concave continuum is detected for 2200{plus}420: the steep low-energy component is consistent with the high-energy tail of the synchrotron emission responsible for the longer wavelengths, while the harder tail at higher energies is the onset of the Compton component. The two BL Lacs were observed with ground-based telescopes from radio to TeV energies contemporaneously with {ital ASCA}. The spectral energy distributions are consistent with synchrotron self-Compton emission from a single homogeneous region shortward of the IR/optical wavelengths, with a second component in the radio domain related to a more extended emission region. For 2200{plus}420, comparing the 1995 November state with the optical/GeV flare of 1997 July, we find that models requiring inverse Compton scattering of external photons provide a viable mechanism for the production of the highest (GeV) energies during the flare. In particular, an increase of the external radiation density and of the power injected in the jet can reproduce the flat {gamma}-ray continuum observed in 1997 July. A directly testable prediction of this model is that the line luminosity in 2200{plus}420 should vary shortly after ({approximately}1 month) a nonthermal synchrotron flare. {copyright} {ital {copyright} 1999.} {ital The American Astronomical Society}},

  doi          = {10.1086/307005},

  url          = {https://www.osti.gov/biblio/353755},
  journal      = {Astrophysical Journal},
number       = 1,

  volume       = 515,

  place        = {United States},

  year         = {Thu Apr 01 00:00:00 EST 1999},

  month        = {Thu Apr 01 00:00:00 EST 1999}

}

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