Rapid synchrotron flares from BL Lacertae detected by ASCA and RXTE

Chiharu Tanihata*, Tadayuki Takahashi, Jun Kataoka, Greg M. Madejski, Susumu Inoue, Hidetoshi Kubo, Fumiyoshi Makino, John R. Mattox, Nobuyuki Kawai

*Corresponding author for this work

Research output: Contribution to journalArticlepeer-review

11 Citations (Scopus)


We report the variable X-ray emission from BL Lacertae detected in the ASCA ToO observation conducted during the EGRET and RXTE pointings, coincident with the 1997 July outburst. The source showed a historically high state of X-ray, optical, and γ-ray emission, with its 2-10 keV flux peaking at ∼3.3 × 10-11 ergs cm-2 s-1. This is more than 3 times higher than the value measured by ASCA in 1995. We detected two rapid flares that occurred only in the soft X-ray band, while the hard X-ray flux also increased, but decayed with a much longer timescale. Together with the requirement of a very steep and varying power law dominating the soft X-ray band in addition to the hard power law, we suggest that both the high-energy end of the synchrotron spectrum and the hard inverse Compton spectrum were visible in this source during the outburst. We discuss the possible origins of the observed variability timescales, and interpret the short timescales of the soft X-ray variability as reflecting the size of the emission region.

Original languageEnglish
Pages (from-to)124-130
Number of pages7
JournalAstrophysical Journal
Issue number1 PART 1
Publication statusPublished - 2000 Nov 1
Externally publishedYes


  • BL Lacertae objects: individual (BL Lacertae)
  • Galaxies: active
  • Radiation mechanisms: nonthermal
  • X-rays: galaxies

ASJC Scopus subject areas

  • Astronomy and Astrophysics
  • Space and Planetary Science


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