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INTEGRAL observation of flaring activity of Mrk 421

ATel #848; G. G. Lichti (MPE, Garching), S. Paltani, M. Mowlavi (ISDC, Geneva), M. Ajello, W. Collmar, A. von Kienlin (MPE, Garching), V. Beckmann (NASA/GSFC), C. Boisson, H. Sol (Obs. Paris), J. Buckley (Washington Univ.), P. Charlot (Bordeaux Obs.), B. Degrange (Ecole Polytechnique Bordeaux), A. Djannati-Atai, M. Punch (College de France), A. Falcone (Penn State Univ.), J. Finley (Purdue Univ.), G. Fossati (Univ. of California San Diego), G. Henri, L. Sauge (Obs. Grenoble), K. Katarzynski (Torun Center), D. Kieda (Univ. of Utah), A. Lähteenmäki, M. Tornikoski (Metsahovi Radio Obs.), K. Mannheim (Univ. von Würzburg), A. Marcowith (CESR, Toulouse), A. Saggione (Centre d'Etudes Nucl., Bordeaux), A. Sillanpaa, L. Takalo (Tuorla Obs.), D. Smith (CENBG, Bordeaux), T. Weekes (Smithsonian Astroph. Obs.)
on 29 Jun 2006; 16:29 UT
Credential Certification: Nami Mowlavi (Nami.Mowlavi@obs.unige.ch)

Subjects: X-ray, AGN

Referred to by ATel #: 1449, 2292

INTEGRAL observed Mrk 421 nearly continuously from June 14, 2006 07:54:19.0 UT until June 25, 2006 19:54:28 UT (and not July 25 as was erroneously written in ATEL #840).

During this time the source was observed to be highly variable in both IBIS/ISGRI and JEM-X. Three flares were observed during this observation, respectively on June 16, 17 and 23. The strongest was the last one (detection significance of 30 sigma in both instruments), with maximal fluxes reaching ~92 mCrab in 3-10 keV, ~120 mCrab in 10-20 keV, ~110 mCrab in 20-40 keV and ~80 mCrab in 40-80 keV. A cutoff power law fit to the 3-200 keV spectrum obtained during the first 12 hours of this flare leads to a spectral index of 1.91 +- 0.03 and a cutoff energy of 98+-16 keV (90% confidence level).

The flare on June 23 was also observed by the BAT of Swift at the 7.5-sigma level (see Bacodine notice from Swift from 23 June 06, 16:06:34 UT). In the energy interval 15 - 150 keV a flux of ~3.6E-2 photons/(cm² s) [~2.3E-9 erg/(cm² s)] was measured, with a power law spectral index of 1.9 +- 0.4 (90% confidence).

Simultaneous ground-based observations were also performed at optical and radio wavelengths.

Since the source seems to remain active further observations at all wavelengths are recommended.