1720027

The goal of this proposal is to better understand the low-flux state and long-term behaviour of blazars at high-energies by studying Mrk 421 with a combination of observations from X-rays to TeV gamma rays. The programconsists of two observations of 370 ks each one in each of the visibility periods in May-June and Nov-Dec. Theseobservations will be enhanced with 2 ks snapshots with focusing X-ray instruments (XMM-NewtonandSwift)and public monitoring programs of the source by Fermi andSwift/XRT. The energy ranges covered respectivelybyINTEGRALandFACTare crucial for modeling the spectral energy distribution (SED) of blazars. Based onan examination of allINTEGRALdata the best candidate among theFACT-monitored TeV blazars is Mrk 421.Short-term variability in high-flux states and flaring are covered by other ToO programs. We want to investigate theevolution of the SED on the timescales of months and with this constrain blazar emission models.INTEGRALisessential for this as it measures the energy region at the decline of the low energy peak and the valley between thelow and high energy peaks. In addition we want to investigate if Mrk 421 exhibits a peak shift and thus a tendencyto extreme behaviour akin to that seen in Mrk 501 and 1ES 2344+51.4. To do so we want to compare the resultsof two observations. Past observations (last one in 2015) have been triggered by the high state of the source andare therefore not suitable for our study. We need these longer observations to learn about the sources long-termbehaviour. There are no long-term observations in the hard X-rays. Any outcome of this study will therefore providean unprecedented look into the high-energy emission of blazars in their non-flaring state [truncated! Please see actual data for full text]