The first <i>Fermi</i> multifrequency campaign on BL Lacertae [electronic resource] : Characterizing the low-activity state of the eponymous blazar
- Washington, D.C. : United States. Dept. of Energy, 2011. and Oak Ridge, Tenn. : Distributed by the Office of Scientific and Technical Information, U.S. Dept. of Energy
- Physical Description:
- Article numbers 101 : digital, PDF file
- Additional Creators:
- SLAC National Accelerator Laboratory, United States. Department of Energy, and United States. Department of Energy. Office of Scientific and Technical Information
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- Free-to-read Unrestricted online access
- Here, we report on observations of BL Lacertae during the first 18 months of <i>Fermi</i> LAT science operations and present results from a 48 day multifrequency coordinated campaign from 2008 August 19 to 2008 October 7. The radio to gamma-ray behavior of BL Lac is unveiled during a low-activity state thanks to the coordinated observations of radio-band (Metsähovi and VLBA), near-IR/optical (Tuorla, Steward, OAGH, and MDM), and X-ray (<i>RXTE</i> and <i>Swift</i>) observatories. No variability was resolved in gamma rays during the campaign, and the brightness level was 15 times lower than the level of the 1997 EGRET outburst. Moderate and uncorrelated variability has been detected in UV and X-rays. The X-ray spectrum is found to be concave, indicating the transition region between the low- and high-energy components of the spectral energy distribution (SED). VLBA observation detected a synchrotron spectrum self-absorption turnover in the innermost part of the radio jet appearing to be elongated and inhomogeneous, and constrained the average magnetic field there to be less than 3 G. Over the following months, BL Lac appeared variable in gamma rays, showing flares (in 2009 April and 2010 January). There is no evidence for the correlation of gamma rays with the optical flux monitored from the ground in 18 months. The SED may be described by a single-zone or a two-zone synchrotron self-Compton (SSC) model, but a hybrid SSC plus external radiation Compton model seems to be preferred based on the observed variability and the fact that it provides a fit closest to equipartition.
- Published through SciTech Connect., 03/10/2011., Astrophysical Journal 730 2 ISSN 0004-637X AM, and Abdo, A.; Ackermann, M.; Ajello, M.; Antolini, E.; Baldini, L.; Ballet, J.; Barbiellini, G.; Bastieri, D.; Bechtol, K.; Bellazzini, R.; Berenji, B.; Blandford, R.; Bonamente, E.; Borgland, A.; Bregeon, J.; Brez, A.; Brigida, M.; Bruel, P.; Buehler, R.; Buson, S.; Caliandro, G.; Cameron, R.; Cannon, A.; Caraveo, P.; Carrigan, S.; et al.
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