We report on two BeppoSAX observations of BL Lac (2200+420) performed respectively in June and December 1999, as part of a ToO program to monitor blazars in high states of activity. During both runs the source has been detected up to 100 keV, but it showed quite different spectra: in June it was concave with a very hard component above 5-6 keV (alpha_1 ~ 1.6; alpha_2 ~ 0.15); in December it was well fitted by a single power law (alpha ~ 0.6). During the first BeppoSAX observation BL Lac showed an astonishing variability episode: the 0.3 - 2 keV flux doubled in ~ 20 minutes, while the flux above 4 keV was almost constant. This frequency-dependent event is one of the shortest ever recordered for BL Lac objects and places lower limits on the dimension and the magnetic field of the emitting region and on the energy of the synchrotron radiating electrons. A similar but less extreme behaviour is detected also in optical light curves, that display non-simultaneous, smaller fluctuations of ~ 20% in 20 min. We fit the spectral energy distributions with a homogeneous, one-zone model to constrain the emission region in a very simple but effective SSC + external Compton scenario, highlightning the importance of the location of the emitting region with respect to the Broad Line Region and the relative spectral shape dependence. We compare our data with historical radio to gamma-ray Spectral Energy Distributions.

BL Lacertae: complex spectral variability and rapid synchrotron flare detected with BeppoSAX / Ravasio, M.; Tagliaferri, G.; Ghisellini, G.; Giommi, P; Nesci, R.; Massaro, E.; Chiappetti, L.; Celotti, Anna Lisa; Costamante, L.; Maraschi, L.; Tavecchio, F.; Tosti, G.; Treves, A.; Wolter, A.; Balonek, T.; Carini, M.; Kato, T.; Kurtanidze, O.; Montagni, F.; Nicolashvili, M.; Noble, J.; Nucciarelli, G.; Raiteri, C. M.; Sclavi, S.; Uemura, M.; Villata, M.. - In: ASTRONOMY & ASTROPHYSICS. - ISSN 0004-6361. - 383:3(2002), pp. 763-772. [10.1051/0004-6361:20011828]

BL Lacertae: complex spectral variability and rapid synchrotron flare detected with BeppoSAX

Celotti, Anna Lisa;
2002

Abstract

We report on two BeppoSAX observations of BL Lac (2200+420) performed respectively in June and December 1999, as part of a ToO program to monitor blazars in high states of activity. During both runs the source has been detected up to 100 keV, but it showed quite different spectra: in June it was concave with a very hard component above 5-6 keV (alpha_1 ~ 1.6; alpha_2 ~ 0.15); in December it was well fitted by a single power law (alpha ~ 0.6). During the first BeppoSAX observation BL Lac showed an astonishing variability episode: the 0.3 - 2 keV flux doubled in ~ 20 minutes, while the flux above 4 keV was almost constant. This frequency-dependent event is one of the shortest ever recordered for BL Lac objects and places lower limits on the dimension and the magnetic field of the emitting region and on the energy of the synchrotron radiating electrons. A similar but less extreme behaviour is detected also in optical light curves, that display non-simultaneous, smaller fluctuations of ~ 20% in 20 min. We fit the spectral energy distributions with a homogeneous, one-zone model to constrain the emission region in a very simple but effective SSC + external Compton scenario, highlightning the importance of the location of the emitting region with respect to the Broad Line Region and the relative spectral shape dependence. We compare our data with historical radio to gamma-ray Spectral Energy Distributions.
383
3
763
772
https://doi.org/10.1051/0004-6361:20011828
https://arxiv.org/abs/astro-ph/0201307
Ravasio, M.; Tagliaferri, G.; Ghisellini, G.; Giommi, P; Nesci, R.; Massaro, E.; Chiappetti, L.; Celotti, Anna Lisa; Costamante, L.; Maraschi, L.; Tavecchio, F.; Tosti, G.; Treves, A.; Wolter, A.; Balonek, T.; Carini, M.; Kato, T.; Kurtanidze, O.; Montagni, F.; Nicolashvili, M.; Noble, J.; Nucciarelli, G.; Raiteri, C. M.; Sclavi, S.; Uemura, M.; Villata, M.
File in questo prodotto:
Non ci sono file associati a questo prodotto.

I documenti in IRIS sono protetti da copyright e tutti i diritti sono riservati, salvo diversa indicazione.

Utilizza questo identificativo per citare o creare un link a questo documento: https://hdl.handle.net/20.500.11767/14607
Citazioni
  • ???jsp.display-item.citation.pmc??? ND
  • Scopus 61
  • ???jsp.display-item.citation.isi??? 64
social impact