Swift/XRT follow-up observation confirms the flaring activity of Mrk 421
ATel #2295; F. D'Ammando (INAF-IASF Roma, Univ. Tor Vergata), M. Perri (ASI Science Data Center), A. Tramacere (ISDC), N. Gehrels (NASA/GSFC), E. Hoversten (PSU), H. A. Krimm (CRESST/GSFC/USRA)
on 13 Nov 2009; 20:25 UT
Credential Certification: Hans A. Krimm (Hans.Krimm@nasa.gov)
Referred to by ATel #: 2368
Motivated by recent flaring activity detected on November 10, 2009 by
the Burst Alert Telescope (BAT) hard X-ray transient monitoring
program (Krimm et al. 2009, ATel #2292), we have performed a Swift
target of opportunity observation of Mrk 421.
We report on the analysis of the Swift/XRT data obtained on November
12. The spectrum of the Swift/XRT observation can be fitted (0.3-10
keV) with a log-parabolic spectral law absorbed by a column density
consistent with the Galactic one in the direction of the source (n_H =
1.61e20 cm-2, Lockman & Savage 1995), a photon index of 1.59+/-0.01
and a spectral curvature of 0.28+/-0.01. The corresponding unabsorbed
2-10 keV (0.3-10 keV) flux is 2.0e-09 (3.5e-09) erg cm-2 s-1. This
flux is only slightly lower than the maximum flux ever observed from
Mrk 421 in soft X-ray by Swift/XRT on June 2008 (Donnarumma et al.
2009, ApJ, 691, L13) and higher than previous observations in flaring
state (Fossati et al. 2008, ApJ, 677, 906; Lichti et al. 2008, A&A,
486, 721). The very high level of flux observed by XRT confirms the
flaring activity previously observed in hard X-rays by BAT.
Swift will continue monitoring Mrk 421 over the next two weeks with five more
observations. Further observations at all wavelengths are encouraged.
We thank the Swift Team for making this observation possible.