ASCA Observation of an X-Ray/TeV Flare from the BL Lacertae Object Markarian 421

Details ASCA Observation of an X-Ray/TeV Flare from the BL Lacertae Object Markarian 421 ASCA Observation of an X-Ray/TeV Flare from the BL Lacertae Object Markarian 421

Oct 1996

adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1996apj...470l..89t&link_type=abstract

Astrophysical Journal Letters v.470, p.L89

Astronomy and Astrophysics

Astronomy

179

Galaxies: Bl Lacertae Objects: General, Galaxies: Bl Lacertae Objects: Individual Name: Markarian 421, X-Rays: General

Scientific paper

We observed the BL Lac object Mrk 421 with the X-ray satellite ASCA in 1994 as part of a multifrequency observation. The 24 hr observation was conducted 1 day after the onset of a TeV flare detected by the Whipple Observatory and detected an X-ray flare, with no apparent variability in the optical, UV, and EGRET GeV flux. The ASCA 2--10 keV flux peaked at 3.7 x 10-10 ergs cm-2 s-1 and then decreased to 1.8 x 10-10 ergs cm-2 s-1 with a doubling timescale of ~12 hr. The shape of the X-ray spectrum varied during the observation, such that the hard X-rays always led the soft X-rays, both in brightening and dimming of the source, with a lag of the 0.5--1 keV photons versus those in the 2--7.5 keV band of ~1 hr. The rapid TeV variability indicates a compact TeV-producing region, suggesting relativistic beaming with a Doppler factor delta >= 5. The correlation of the flux in the X-ray and the TeV bands indicates that a high-energy tail of a single electron population is responsible for both X-rays and TeV gamma -rays, with radio, IR, UV and X-rays produced via the synchrotron process and GeV and TeV gamma -rays produced via Comptonization. Under the assumption that the "soft lag" observed in the X-ray band is due to the synchrotron-lifetime effects, with delta = 5, we calculate the magnetic field for the X-ray--producing region to be ~0.2 G. The Lorentz factors gamma el of the electrons responsible for the emission in the keV and TeV bands are ~106, consistent with the values implied by the Klein-Nishina limit.

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