Swift/XRT follow-up observation confirms the flaring activity of Mrk 421

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.