2010A&A...524A..43R


C.D.S. - SIMBAD4 rel 1.7 - 2020.06.04CEST23:48:16

2010A&A...524A..43R - Astronomy and Astrophysics, volume 524, A43-43 (2010/12-1)

Another look at the BL Lacertae flux and spectral variability. Observations by GASP-WEBT, XMM-Newton, and Swift in 2008-2009.

RAITERI C.M., VILLATA M., BRUSCHINI L., CAPETTI A., KURTANIDZE O.M., LARIONOV V.M., ROMANO P., VERCELLONE S., AGUDO I., ALLER H.D., ALLER M.F., ARKHAROV A.A., BACH U., BERDYUGIN A., BLINOV D.A., BOETTCHER M., BUEMI C.S., CALCIDESE P., CAROSATI D., CASAS R., CHEN W.-P., COLOMA J., DILTZ C., DI PAOLA A., DOLCI M., EFIMOVA N.V., FORNE E., GOMEZ J.L., GURWELL M.A., HAKOLA A., HOVATTA T., HSIAO H.Y., JORDAN B., JORSTAD S.G., KOPTELOVA E., KURTANIDZE S.O., LAEHTEENMAEKI A., LARIONOVA E.G., LETO P., LINDFORS E., LIGUSTRI R., MARSCHER A.P., MOROZOVA D.A., NIKOLASHVILI M.G., NILSSON K., ROS J.A., ROUSTAZADEH P., SADUN A.C., SILLANPAEAE A., SAINIO J., TAKALO L.O., TORNIKOSKI M., TRIGILIO C., TROITSKY I.S. and UMANA G.

Abstract (from CDS):

In a previous study we suggested that the broad-band emission and variability properties of BL Lacertae can be accounted for by a double synchrotron emission component with related inverse-Compton emission from the jet, plus thermal radiation from the accretion disc. Here we investigate the matter with further data extending over a wider energy range. The GLAST-AGILE Support Program (GASP) of the whole earth blazar telescope (WEBT) monitored BL Lacertae in 2008-2009 at radio, near-IR, and optical frequencies to follow its flux behaviour. During this period, high-energy observations were performed by XMM-Newton, Swift, and Fermi. We analyse these data with particular attention to the calibration of Swift UV data, and apply a helical jet model to interpret the source broad-band variability. The GASP-WEBT observations show an optical flare in 2008 February-March, and oscillations of several tenths of mag on a few-day time scale afterwards. The radio flux is only mildly variable. The UV data from both XMM-Newton and Swift seem to confirm a UV excess that is likely caused by thermal emission from the accretion disc. The X-ray data from XMM-Newton indicate a strongly concave spectrum, as well as moderate (∼4-7%) flux variability on an hour time scale. The Swift X-ray data reveal fast (interday) flux changes, not correlated with those observed at lower energies. We compare the spectral energy distribution (SED) corresponding to the 2008 low-brightness state, which was characterised by a synchrotron dominance, to the 1997 outburst state, where the inverse-Compton emission was prevailing. A fit with an inhomogeneous helical jet model suggests that two synchrotron components are at work with their self inverse-Compton emission. Most likely, they represent the radiation from two distinct emitting regions in the jet. We show that the difference between the source SEDs in 2008 and 1997 can be explained in terms of pure geometrical variations. The outburst state occurred when the jet-emitting regions were better aligned with the line of sight, producing an increase of the Doppler beaming factor. Our analysis demonstrates that the jet geometry can play an extremely important role in the BL Lacertae flux and spectral variability. Indeed, the emitting jet is probably a bent and dynamic structure, and hence changes in the emitting regions viewing angles are likely to happen, with strong consequences on the source multiwavelength behaviour.

Abstract Copyright:

Journal keyword(s): galaxies: active - BL Lacertae objects: general - BL Lacertae objects: individual: BL Lacertae - galaxies: jets

Status at CDS:  

Simbad objects: 4

goto Full paper

goto View the reference in ADS

Number of rows : 4

N Identifier Otype ICRS (J2000)
RA
ICRS (J2000)
DEC
Mag U Mag B Mag V Mag R Mag I Sp type #ref
1850 - 2020
#notes
1 Mrk 421 BLL 11 04 27.3139210166 +38 12 31.798324828   13.50 12.90 8.31   ~ 2376 1
2 * alf Lyr dS* 18 36 56.33635 +38 47 01.2802 0.03 0.03 0.03 0.07 0.10 A0Va 2503 0
3 NAME BL Lac BLL 22 02 43.2913773726 +42 16 39.978417860   15.66 14.72     ~ 2002 1
4 3C 454.3 QSO 22 53 57.74798 +16 08 53.5611   16.57 16.10 15.22   ~ 2494 2

    Equat.    Gal    SGal    Ecl

To bookmark this query, right click on this link: simbad:objects in 2010A&A...524A..43R and select 'bookmark this link' or equivalent in the popup menu


2020.06.04-23:48:16

© Université de Strasbourg/CNRS

    • Contact