Very high energy gamma-ray emission from the BL Lac object Markarian 421 has been detected over three observing seasons on 59 nights between April 1992 and June 1994 with the Whipple 10-meter imaging Cherenkov telescope. During its initial detection in 1992, its flux above 500 GeV was 1.6×10−11photons cm−2 s−1. Observations in 1993 confirmed this level of emission. For observations made between...

Context. BL Lac objects undergo strong flux variations involving considerable changes in their spectral shapes. We specifically investigate the X-ray spectral evolution of Mrk 421 over a time span of about nine years. Aims. We aim at statistically describing and physically understanding the large spectral changes in X rays observed in Mrk 421 over this time span. Methods. We perform a homogeneo...

The TeV-emitting BL Lac object Mkn 421 was observed with very long baseline interferometry (VLBI) at three closely-spaced epochs one-month apart in March–April 1998. The source was also monitored at very-high γ-ray energies (TeV measurements) during the same period in an attempt to search for correlations between TeV variability and the evolution of the radio morphology on parsec scales. While ...

The origin of the gamma-ray emission blazar Mrk 421 is still a matter debate. We used 5.5 years unbiased observing campaign data, obtained using FACT telescope and Fermi LAT detector at TeV GeV energies, longest densest so far, together with contemporaneous multi-wavelength observations, to characterise variability constrain underlying physical mechanisms. studied correlated light curves by ten...

I. UNIQUE IDENTIFIERS ............................................................... 421 A. James Grimmelmann and @grimmelm .................................. 422 B. Unique Identifiers ................................................................. 424 C. Other Examples .................................................................... 426 II. CONSEQUENCES ....................................

1 Topological Spaces 1 1.1 Continuity and Topological Spaces . . . . . . . . . . . . . . . 1 1.2 Topological Spaces . . . . . . . . . . . . . . . . . . . . . . . . 1 1.3 Metric Spaces . . . . . . . . . . . . . . . . . . . . . . . . . . . 1 1.4 Further Examples of Topological Spaces . . . . . . . . . . . . 3 1.5 Closed Sets . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4 1.6 Hausdorff ...