N. Galante

Veritas: Status summary 2009

VERITAS is a ground-based gamma-ray observatory that uses the imaging atmospheric Cherenkov technique and operates in the very-high energy (VHE) region of the gamma-ray spectrum from 100 GeV to 50 TeV. The observatory consists of an array of four 12 m-diameter imaging atmospheric Cherenkov telescopes located in southern Arizona, USA. The four-telescope array has been fully operational since September 2007, and over the last two years, VERITAS has been operating with high reliability and sensitivity. It is currently one of the most sensitive VHE observatories. This paper summarizes the status of VERITAS as of October 2009, and describes the detection of several new VHE gamma-ray sources.

Status and highlights of VERITAS

VERITAS (Very Energetic Radiation Imaging Telescope Array System) is an array of atmospheric Cherenkov telescopes sensitive to very high energy (VHE) γ-rays above 100 GeV. Located at the Fred Lawrence Whipple Observatory in southern Arizona, USA, the VERITAS array of four 12m-diameter telescopes began full operation in September 2007. Two major upgrades, the relocation of telescope 1 in Summer 2009 and the upgrade of the level-2 trigger in Fall 2011, made VERITAS the most sensitive VHE instrument in the northern hemisphere. The VERITAS Collaboration consists of scientists from institutions in the USA, Canada, Germany and Ireland. VERITAS is performing observations that cover a broad range of science topics, including the study of galactic and extragalactic astrophysical sources of VHE radiation and the study of particle astrophysics, such as the indirect search for dark matter in astrophysical environments. The VERITAS observational campaigns resulted in the detection of 40 VHE sources, including the disc...

Monitoring of Bright Blazars with MAGIC in the 2007/2008 Season

Because of the short duty‐cycles and observation‐time constraints, studies of bright TeV (E>100 GeV) blazars are mostly restricted to flaring episodes or rather short (days to few weeks) multiwavelength campaigns. At the same time, long‐term studies of these objects are essential to gain a more complete understanding of the blazar phenomenon and to constrain theoretical models concerning jet physics. Only unbiased long‐term studies are adequate for the determination of flaring state probabilities and for estimating the statistical significance of possible correlations between TeV flaring states and other wavebands or observables, such as neutrino events. Regular observations also provide triggers for multiwavelength ToO observations originating from the TeV waveband. These are particularly needed to identify and study orphan TeV flares, i.e. flares without counterparts in other wavebands. In 2007/8 the MAGIC telescope has monitored three TeV blazars on a regular basis: Mrk 501, Mrk 421, and 1ES 1959+650. ...

Observation of gamma ray bursts at very high energies with the MAGIC telescope

The detection of the Very High Energy (VHE) emission from Gamma Ray Bursts (GRBs) is desired, as it will provide an unprecedented opportunity to enlighten the nature of the central engine and the interaction between the relativistic flow and the environment of the burst progenitor. Thanks to its large reflector size, high quantum efficiency photomultipliers and sophisticated trigger logic, the MAGIC telescope is currently the most sensitive detector at energies around 100 GeV. In addition, thanks to its fast repositioning time, MAGIC is able to start the GRB follow‐up observation, triggered by an alert from the GRB Coordinates Network (GCN), on average within 45s after the burst onset T0. In the past years of operation several simultaneous GRB observations of the prompt and early afterglow emission phase with satellite experiments were performed by MAGIC. However, until now without successful detection of VHE γ‐rays above threshold energies >80 GeV. The computed upper limits are compatible with a power la...

Gamma-ray burst observations with new generation imaging atmospheric Cerenkov Telescopes in the FERMI era

After the launch and successful beginning of operations of the FERMI satellite, the topics related to high‐energy observations of gamma‐ray bursts have obtained a considerable attention by the scientific community. Undoubtedly, the diagnostic power of high‐energy observations in constraining the emission processes and the physical conditions of gamma‐ray burst is relevant. We briefly discuss how gamma‐ray burst observations with ground‐based imaging array Cerenkov telescopes, in the GeV‐TeV range, can compete and cooperate with FERMI observations, in the MeV‐GeV range, to allow researchers to obtain a more detailed and complete picture of the prompt and afterglow phases of gamma‐ray bursts.

Observation and Upper Limits of GRBs with the MAGIC Telescope

After three years since the beginning of operation, the MAGIC telescope could observe several GRB events in the prompt and early afterglow phase. Thanks to its innovative design, the telescope could promptly react to incoming GCN alerts and rapidly slew to the burst coordinates within a typical delay of 50 seconds, performing observations with an energy threshold spanning from 80 to 200 GeV. The observations did not reveal any γ‐ray emission. The computed upper limits are compatible with a power law extrapolation, where intrinsic fluxes are evaluated taking into account the attenuation due to the scattering with the Extragalactic Background Light.

Observation of GRBs with the MAGIC Telescope

After three years since the beginning of operation, the MAGIC telescope could observe several GRB events in the prompt and early afterglow phase. Thanks to its innovative design, the telescope could promptly react to incoming GCN alerts and rapidly slew to the burst coordinates within a typical delay of 50 seconds, performing observations with an energy threshold spanning from 80 to 200 GeV. The observations did not reveal any γ‐ray emission. The computed upper limits are compatible with a power law extrapolation, where intrinsic fluxes are evaluated taking into account the attenuation due to the scattering with the Extragalactic Background Light.

MAGIC Observation of the Prompt and Afterglow Emission from GRBs

During two years since the beginning of operation, the MAGIC telescope could observe several GRB events in the prompt and early afterglow phase. Thanks to its innovative design, the telescope could promptly react to incoming GCN alerts, rapidly slew to the burst coordinates within on average 45 seconds, performing observations with an energy threshold spanning from 80 to 200 GeV. The observations did not reveal any γ‐ray emission. The computed upper limits are compatible with a power law extrapolation, where intrinsic fluxes are evaluated taking into account the attenuation due to the scattering in the Metagalactic Radiation Field.