Scientific Justification
The Fermi/AGN group is organizing a multi-frequency campaign on the object Mrk421. Specially critical are the frequencies around the peaks of the Synchrotron (~keV) and Inverse Compton (10-100 GeV) bumps. Swift observations are important to provide information from energies in the range 0.2-10 keV (which complements the observations from RXTE/PCA above 3 keV) as well as information at the Ultraviolet frequencies (which are not affected by the host galaxy emission). Note that observations at UV frequencies can only be provided by Swift. Both X-rays and UV frequencies are very valuable for the correct modeling of the Synchrotron bump, and hence Swift observations will play a key role in the understanding of the physical processes occurring in this blazar.
The source is bright at both X-rays and UV frequencies, and hence 1 ks observation is long enough to have very significant detections with both XRT and UVOT instruments. We request Swift 1ks long observations every 3 days starting from December 8th and finishing on April 1st 2010. This is 58 ks in total. Those Swift observations will be combined with the already scheduled optical,X-ray and TeV observations, as well as with Fermi/LAT, which operates in survey mode and hence is "constantly" observing Mrk421.
The current schedule of the multi-frequency observations from this campaign can be found at the following URL:
https://confluence.slac.stanford.edu/display/GLAMCOG/Campaign+on+Mrk421+%28December+2009+to+December+2010%29
The scientific return of the Swift data will be maximized if the observations are taken close in time to the (almost simultaneous) optical, RXTE and IACT observations. Yet we want to stress that these observations are requested within the constraints of the primary Swift observing program. We are aware of the very tight Swift observing schedule, and thus we only ask for a "best effort" from the Swift team.