Variability pattern and the spectral evolution of the BL lacertae object PKS 2155-304

Jun Kataoka, T. Takahashi, F. Makino, S. Inoue, G. M. Madejski, M. Tashiro, C. M. Urry, H. Kubo

Research output: Contribution to journalArticle

106 Citations (Scopus)

Abstract

The TeV blazar PKS 2155-304 was monitored with the X-ray satellite ASCA in 1994 May as part of a multiwavelength campaign from the radio to X-ray bands. At the beginning of the two-day continuous observation, we detected a large flare, in which the 2-10 keV flux changed by a factor of 2 on a timescale of 3 × 104 s. During the flare, the increase in the hard X-ray flux clearly preceded that observed in the soft X-rays, with the spectral evolution tracking a "clockwise loop" in the flux versus photon index plane. Ascribing the energy-dependent variability to differential synchrotron cooling of relativistic electrons, we estimate the magnetic field B in the emission region. We tested two different methods of comparing the time series in various X-ray bands: (1) fitting the light curves to a Gaussian function and searching for the time shift of the peak of the flare, and (2) calculating the discrete correlation function. Both methods yielded a consistent solution of B ∼ 0.1 G. We also found that the flare amplitude becomes larger as the photon energy increases, while the duration of the flare stays roughly constant throughout the ASCA energy band (0.7-7.5 keV). In the framework of the time-dependent synchrotron self-Compton model in a homogeneous region, we consider a flare where the maximum Lorentz factor (γmax) of the injected electrons increases uniformly throughout the emission volume. The temporal evolution of spectra as well as the light curves were reproduced with the physical parameters self-consistently determined from seven observables. We obtained B ∼ 0.1-0.2 G and a region size R ∼ 10-2 pc for relativistic beaming with a Doppler factor of δ ∼ 20-30. We discuss the significance of light-travel time effects.

Original languageEnglish
Pages (from-to)243-253
Number of pages11
JournalAstrophysical Journal
Volume528
Issue number1 PART 1
Publication statusPublished - 2000 Jan 1
Externally publishedYes

Fingerprint

BL Lacertae objects
flares
x rays
light curve
synchrotrons
energy
electron
temporal evolution
travel time
photons
guy wires
travel
energy bands
time series
radio
magnetic field
cooling
timescale
electrons
shift

Keywords

  • BL Lacertae objects: individual (PKS 2155-304)
  • Gamma rays: theory
  • Radiation mechanisms: nonthermal
  • X-rays: galaxies

ASJC Scopus subject areas

  • Space and Planetary Science

Cite this

Kataoka, J., Takahashi, T., Makino, F., Inoue, S., Madejski, G. M., Tashiro, M., ... Kubo, H. (2000). Variability pattern and the spectral evolution of the BL lacertae object PKS 2155-304. Astrophysical Journal, 528(1 PART 1), 243-253.

Variability pattern and the spectral evolution of the BL lacertae object PKS 2155-304. / Kataoka, Jun; Takahashi, T.; Makino, F.; Inoue, S.; Madejski, G. M.; Tashiro, M.; Urry, C. M.; Kubo, H.

In: Astrophysical Journal, Vol. 528, No. 1 PART 1, 01.01.2000, p. 243-253.

Research output: Contribution to journalArticle

Kataoka, J, Takahashi, T, Makino, F, Inoue, S, Madejski, GM, Tashiro, M, Urry, CM & Kubo, H 2000, 'Variability pattern and the spectral evolution of the BL lacertae object PKS 2155-304', Astrophysical Journal, vol. 528, no. 1 PART 1, pp. 243-253.
Kataoka J, Takahashi T, Makino F, Inoue S, Madejski GM, Tashiro M et al. Variability pattern and the spectral evolution of the BL lacertae object PKS 2155-304. Astrophysical Journal. 2000 Jan 1;528(1 PART 1):243-253.
Kataoka, Jun ; Takahashi, T. ; Makino, F. ; Inoue, S. ; Madejski, G. M. ; Tashiro, M. ; Urry, C. M. ; Kubo, H. / Variability pattern and the spectral evolution of the BL lacertae object PKS 2155-304. In: Astrophysical Journal. 2000 ; Vol. 528, No. 1 PART 1. pp. 243-253.
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