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The accretion of matter onto a massive black hole is believed to feed the relativistic plasma jets found in many active galactic nuclei (AGN). Although some AGN accelerate particles to energies exceeding 10(12) electron volts and are bright sources of very-high-energy (VHE) gamma-ray emission, it is not yet known where the VHE emission originates. Here we(More)
The detection of spectral variability of the γ-ray blazar Mrk 421 at TeV energies is reported. Observations with the Whipple Observatory 10 m γ-ray telescope taken in 2000/2001 revealed exceptionally strong and long-lasting flaring activity. Flaring levels of 0.4 to 13 times that of the Crab Nebula flux provided sufficient statistics for a detailed study of(More)
We report the detection of pulsed gamma rays from the Crab pulsar at energies above 100 giga-electron volts (GeV) with the Very Energetic Radiation Imaging Telescope Array System (VERITAS) array of atmospheric Cherenkov telescopes. The detection cannot be explained on the basis of current pulsar models. The photon spectrum of pulsed emission between 100(More)
The core-dominated radio-loud quasar PKS 0637-752 (z = 0.654) was the first celestial object observed with the Chandra X-ray Observatory, offering the early surprise of the detection of a remarkable X-ray jet. Several observations with a variety of detector configurations contribute to a total exposure time with the Chandra Advanced CCD Imaging Spectrometer(More)
We report the detection of very high-energy γ-ray emission from the intermediate-frequencypeaked BLLacertae object WComae (z = 0.102) by VERITAS, an array of four imaging atmospheric-Cherenkov telescopes. The source was observed between January and April 2008. A strong outburst of γ-ray emission was measured in the middle of March, lasting for only four(More)
The BL Lac object 3C 66A was the target of an extensive multiwavelength monitoring campaign from July 2003 through April 2004 (with a core campaign from Sept. – Dec. 2003), involving observations throughout the electromagnetic spectrum. Radio, infrared, and optical observations were carried out by the WEBT-ENIGMA collaboration. At higher energies, 3C 66A(More)
As a brief revision, the origin of heavy elements and the role of abundances in extremely metal-poor (EMP) stars are presented. Heavy element abundances in the EMP uranium-rich star CS 31082-001 based mainly on near-UV spectra from STIS/HST are presented. These results should be useful for a better characterisation of the neutron exposure(s) that produced(More)
The BL Lac object (blazar) Mrk 421 was observed during its outburst in April 2004 with the Whipple 10 m telescope for a total of about 24.5 hours. The measured γ-ray rate varied substantially over the range from 4 to 10 γ’s/min and eventually exceeded the steady γ-ray rate of the Crab Nebula (standard candle) by a factor of 3. The overall significance of(More)
Blazars have traditionally been separated into two broad categories based upon their optical emission characteristics. Blazars with faint or no emission lines are referred to as BL Lacertae objects (BL Lacs), and blazars with prominent, broad emission lines are commonly referred to as flat spectrum radio quasars (FSRQs). The spectral energy distribution of(More)