arXiv subjects

Darko Zarić

Publications and source records attributed to Darko Zarić.

4 recordsLinked to original sources

arXiv2019

MAGIC observations of Dragonfly Nebula at TeV Energies using the Very Large Zenith Angle Technique

One of the brightest regions of diffuse gamma-ray emission in the northern sky is the Cygnus star-forming region, where one can assume the most energetic processes are taking place. The Dragonfly Nebula (MGRO J2019+37) is one of the brightest sources in the Cygnus region. First discovered by MILAGRO, it was later resolved into two sources by VERITAS: the faint point-like source VER J2016+371 and the bright extended source VER J2019+368. The latter accounts for the bulk of the MGRO J2019+37 emission, with the spectrum among the hardest in the TeV range. We report the results of a dedicated MAGIC observational campaign of VER J2019+368. The data obtained with the Very Large Zenith Angle observational technique provides an effective collection area of about one square kilometer. We used $\sim$45 hours of data collected under Very Large Zenith Angles for exploring the flux of the source at TeV energies.

astro-ph.HE↗

arXiv2019

Searching for Variability of the Crab Nebula Flux at TeV Energies using MAGIC Very Large Zenith Angle Observations

The Crab nebula was once considered to be a stable source until strong flares, up to 30 times increase in flux, were observed in the MeV and GeV energy range by the AGILE and Fermi Gamma-ray Observatories. Existing nebula models often assume that the electron population emitting synchrotron radiation at lower energies is responsible for the VHE emission via Inverse Compton (IC) scattering. This suggests that the variability of the synchrotron $γ$-ray emission may also become observable in the multi-TeV energy range. Until now, no variability in the Crab Nebula flux has been found in the VHE regime. In 2015, MAGIC started an observational campaign which improved the collection efficiency of $γ$-rays above several tens of TeV. These observations are performed under Very Large Zenith Angles (VLZA) and lead to a large increase in the collection area. This allows us to observe the low fluxes at TeV energies in a shorter time compared to standard observations, and to significantly increase the observable energy towards higher energies. We have studied the Crab Nebula light curve obtained from the VLZA data since 2015 in search for the flux variability at the highest TeV energies. The results of this study will be presented.

astro-ph.HE↗

arXiv2019

The Crab Nebula Spectrum at ~100 TeV Measured with MAGIC under Very Large Zenith Angles

The Crab Nebula was discovered as the first very-high-energy gamma-ray source by the Whipple Observatory in 1989. Thirty years after its discovery it is still the reference source and the standard candle for Imaging Atmospheric Cherenkov Telescopes (IACTs). Its spectrum has been measured from the cm radio band to energies up to tens of TeV. Some studies reported a possible but still debated cut-off in its spectrum at few tens of TeV. The MAGIC collaboration is currently investigating the spectrum of the Crab Nebula by using the Very Large Zenith Angle observation technique. The latter provides a significantly increased collection area for energies above 10 TeV. The details of these MAGIC observations will be presented.

astro-ph.IM↗

arXiv2019

Pointing System for the Large Size Telescopes Prototype of the Cherenkov Telescope Array

The pointing system of the prototype of the Large Size Telescope (LST-1) for the Cherenkov Telescope Array observatory, should ensure mapping of the gamma-ray image of a point-like source in the Cherenkov camera to the sky coordinates with a precision better than 14 arcseconds. Detailed studies of the telescope deformations are performed in order to disentangle different deformations and quantify their contributions to the miss-pointing, to learn how to correct for them, and finally how to design the system for offline and online pointing corrections. The LST-1 pointing precision system consist of several devices mounted at the center of the dish: Starguider Camera (SG), Camera Displacement Monitor (CDM), two inclinometers, four distance meters, and an Optical Axis Reference Laser (OARL), working together with the LEDs mounted in a circle around the Cherenkov camera. The online pointing corrections are based on a bending model as currently done by existing IACTs. The offline corrections will be performed combining measurements done by the SG and CDM cameras. SG will provide the position of the Cherenkov camera center with respect to the sky coordinates with a precision of 5 arcseconds, while CDM will provide the deviation of the telescope optical axis defined by the OARL spots with respect to the Cherenkov camera center with a precision better than 5 arcseconds. Laboratory measurements on dedicated test benches showed that the required pointing precision can be achieved for SG, CDM and inclinometer.

astro-ph.IM↗