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Title: Near-infrared and gamma-ray monitoring of TANAMI gamma-ray bright sources

Abstract

Context. We present that spectral energy distribution and its variability are basic tools for understanding the physical processes operating in active galactic nuclei (AGN). Aims. In this paper we report the results of a one-year near-infrared (NIR) and optical monitoring of a sample of 22 AGN known to be gamma-ray emitters, aimed at discovering correlations between optical and gamma-ray emission. Methods. We observed our objects with the Rapid Eye Mount (REM) telescope in J,H,K, and R bands nearly twice every month during their visibility window and derived light curves and spectral indexes. We also analyzed the gamma-ray data from the Fermi gamma-ray Space Telescope, making weekly averages. Results. Six sources were never detected during our monitoring, proving to be fainter than their historical Two micron all sky survey (2MASS) level. All of the sixteen detected sources showed marked flux density variability, while the spectral indexes remained unchanged within our sensitivity limits. Steeper sources showed, on average, a larger variability. From the NIR light curves we also computed a variability speed index for each detected source. Only one source (PKS 0208-512) underwent an NIR flare during our monitoring. Half of the sources showed a regular flux density trend on a one-yearmore » time scale, but do not show any other peculiar characteristic. The broadband spectral index α ro appears to be a good proxy of the NIR spectral index only for BL Lac objects. No clear correlation between NIR and gamma-ray data is evident in our data, save for PKS 0537-441, PKS 0521-360, PKS 2155-304, and PKS 1424-418. In conclusion, the gamma-ray/NIR flux ratio showed a large spread, QSO being generally gamma-louder than BL Lac, with a marked correlation with the estimated peak frequency (ν peak) of the synchrotron emission.« less

Authors:
 [1];  [2];  [3];  [4];  [5]
  1. INAF-IAPS, via Fosso del Cavaliere 100, Roma (Italy); Universita La Sapienza, Roma (Italy)
  2. Universita di Perugia (Italy)
  3. Nordic Optical Telescope (Spain)
  4. NASA Goddard Space Flight Center, Astrophysics Science Division, Greenbelt, MD (United States); Catholic University of America, Washington, DC (United States). Institute for Astrophysics & Computational Sciences
  5. Univ. Wurzburg (Germany). Institut fur Theoretische Physik und Astrophysik, Lehrstuhl fur Astronomie; Dr. Karl-Remeis-Sternwarte and Erlangen Centre for Astroparticle Physics (Germany)
Publication Date:
Research Org.:
SLAC National Accelerator Lab., Menlo Park, CA (United States)
Sponsoring Org.:
USDOE
Contributing Org.:
Fermi-LAT Collaboration
OSTI Identifier:
1356584
Grant/Contract Number:  
AC02-76SF00515
Resource Type:
Accepted Manuscript
Journal Name:
Astronomy and Astrophysics
Additional Journal Information:
Journal Volume: 555; Journal ID: ISSN 0004-6361
Publisher:
EDP Sciences
Country of Publication:
United States
Language:
English
Subject:
79 ASTRONOMY AND ASTROPHYSICS; BL Lacertae objects: general; radiation mechanisms: non-thermal; gamma rays: galaxies

Citation Formats

Nesci, R., Tosti, G., Pursimo, T., Ojha, R., and Kadler, M. Near-infrared and gamma-ray monitoring of TANAMI gamma-ray bright sources. United States: N. p., 2013. Web. doi:10.1051/0004-6361/201321094.
Nesci, R., Tosti, G., Pursimo, T., Ojha, R., & Kadler, M. Near-infrared and gamma-ray monitoring of TANAMI gamma-ray bright sources. United States. doi:10.1051/0004-6361/201321094.
Nesci, R., Tosti, G., Pursimo, T., Ojha, R., and Kadler, M. Tue . "Near-infrared and gamma-ray monitoring of TANAMI gamma-ray bright sources". United States. doi:10.1051/0004-6361/201321094. https://www.osti.gov/servlets/purl/1356584.
@article{osti_1356584,
title = {Near-infrared and gamma-ray monitoring of TANAMI gamma-ray bright sources},
author = {Nesci, R. and Tosti, G. and Pursimo, T. and Ojha, R. and Kadler, M.},
abstractNote = {Context. We present that spectral energy distribution and its variability are basic tools for understanding the physical processes operating in active galactic nuclei (AGN). Aims. In this paper we report the results of a one-year near-infrared (NIR) and optical monitoring of a sample of 22 AGN known to be gamma-ray emitters, aimed at discovering correlations between optical and gamma-ray emission. Methods. We observed our objects with the Rapid Eye Mount (REM) telescope in J,H,K, and R bands nearly twice every month during their visibility window and derived light curves and spectral indexes. We also analyzed the gamma-ray data from the Fermi gamma-ray Space Telescope, making weekly averages. Results. Six sources were never detected during our monitoring, proving to be fainter than their historical Two micron all sky survey (2MASS) level. All of the sixteen detected sources showed marked flux density variability, while the spectral indexes remained unchanged within our sensitivity limits. Steeper sources showed, on average, a larger variability. From the NIR light curves we also computed a variability speed index for each detected source. Only one source (PKS 0208-512) underwent an NIR flare during our monitoring. Half of the sources showed a regular flux density trend on a one-year time scale, but do not show any other peculiar characteristic. The broadband spectral index αro appears to be a good proxy of the NIR spectral index only for BL Lac objects. No clear correlation between NIR and gamma-ray data is evident in our data, save for PKS 0537-441, PKS 0521-360, PKS 2155-304, and PKS 1424-418. In conclusion, the gamma-ray/NIR flux ratio showed a large spread, QSO being generally gamma-louder than BL Lac, with a marked correlation with the estimated peak frequency (νpeak) of the synchrotron emission.},
doi = {10.1051/0004-6361/201321094},
journal = {Astronomy and Astrophysics},
number = ,
volume = 555,
place = {United States},
year = {2013},
month = {6}
}

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