Mini-Workshop for High Energy Gamma Ray Astrophysics

Tuesday 31 Jan 2017, 10:00 → 17:00 Europe/Berlin

Auditorium (MPI Meeting rooms)

Talks 25 min + 20 min discussion each

1 Search for high-confidence blazar candidates and their MWL counterparts in the Fermi-LAT catalog using machine learning

Abstract: The Large Area Telescope (LAT) on board the Fermi satellite conducted the deepest all-sky survey in gamma-rays so far. Despite outstanding achievements in assigning source types, 1010 sources in the Third Fermi-LAT Source Catalog (3FGL) remain without plausible associations, and 573 sources are associated to active galaxies of uncertain type. Assigning blazar classes to unassociated and uncertain sources, and linking counterparts to the unassociated ones, will refine tremendously our knowledge of the population of gamma-ray emitting objects. The application of machine learning algorithms has become an integral part of exploring astrophysical data. Previous machine learning strategies to assign source types were based solely on properties extracted from gamma-ray observations. The extension to multiwavelength information, especially the relation between properties extracted from different parts of the energy spectrum, provides additional source type specific characteristics for better classification. At the same time, it offers the possibility to determine the most likely corresponding counterpart. The source localization accuracy of Fermi measurements is in the order of several arcminutes. Typically several hundred possible counterparts are located within this region, making the association ambiguous. To figure out the most likely counterpart, the associated sample is used to train machine learning classification algorithms. For any particular 3FGL source, all possible combinations with measurements of one additional energy range are considered, e.g. from the Wide-Field Infrared Survey Explorer (WISE) source catalog, or the Swift X-ray Point Source (1SXPS) catalog. By merging the most probable candidates of each of those studies, the power of multiwavelength strategies is exploited and conclusions with even higher confidence concerning blazar counterpart candidates are drawn. In this talk, results of the application of this novel wavelength-dependent approach are presented, and future prospects regarding CTA and possibilities for further physics projects are given.

Speaker: Ms Sabrina Einecke (TU Dortmund)

2 Towards precision VHE gamma-ray astronomy in the CTA-LST era

Abstract: Ground-based observation of celestial objects with Imaging Air Cherenkov Telescopes (IACTs) is the key astronomical technique in the gamma-ray energy range between ~30GeV and ~100TeV, revealing the physics behind the most energetic processes in our Universe. Steady technological progress in this relatively young field of astronomy is pushing on the sensitivity limits of IACTs. This development is about to culminate in the upcoming Cherenkov Telescope Array (CTA) and especially the Large Size Telescopes (LSTs) which provide the lowest energy threshold with unprecedented energy and angular resolution. Due to the indirect nature of the IACT technique, large effort has to be made for controlling and minimizing systematic uncertainties. The higher sensitivity and the better angular resolution quest for new analysis techniques for extended and complex morphology gamma-ray sources. In this talk I will show proven developments which I led or strongly participated in that can serve as basis for further advances into the CTA-LST era.

Speaker: Dr Christian Fruck (Max-Planck-Institut für Physik)

Slides Fruck_Christian

3 Pulsars with Cherenkov Telescopes and the H.E.S.S. I upgrade

Abstract: Pulsars are compact, rotating, magnetized neutron stars, whose non-thermal emission is observed as regular pulsations across the electromagnetic spectrum. Very few pulsars emit pulsed γ-rays above few tens of GeV; observations of this phenomenon are important to improve our understanding of the acceleration and emission mechanisms at play in their magnetospheres. Cherenkov telescopes with large mirrors, like MAGIC and H.E.S.S. II, are the only instruments capable of carrying out such observations with the sensitivity required. In 2014, the Vela pulsar was detected by H.E.S.S. II with high significance. This detection showed the capabilities of this instrument but also its main weakness, namely the monoscopic operation. “Hybrid” operation is desirable since it would heavily suppress background noise and reduce systematics, but it was difficult to carry out below 100 GeV because of the dead-time of the H.E.S.S. I cameras. In order to reduce the dead-time and improve the reliability of the whole array for the next 5 years, a major upgrade of the four older H.E.S.S. I cameras has been carried out between 2013 and 2016. As of end January 2017, the upgraded system has been commissioned and is about to be handed over to the H.E.S.S. collaboration for resuming regular observations.

Speaker: Gianluca Giavitto (DESY Zeuthen)

4 First results from H.E.S.S. II and implications for CTA

Abstract: The High Energy Stereoscopic System (H.E.S.S.) is an array of Imaging Atmospheric Cherenkov Telescopes (IACTs) located in the Khomas Highland of Namibia. The array, which initially consisted of four 12 m telescopes, was recently complemented with a 28 m telescope, marking the start of H.E.S.S. Phase II. The new telescope, dubbed CT5, potentially extends the energy range covered by H.E.S.S. down to ∼ 30 GeV. Such an extension of the instrument's energy range is particularly beneficial for studies of transient phenomena and variable sources with soft spectra, such as Gamma-Ray Bursts (GRBs) and Active Galactic Nuclei (AGNs) located at high redshifts (> 0.5), as well as gamma-ray pulsars. We will review the first results from H.E.S.S. II, with an emphasis on the AGN measurements at low energies. In particular, recent results on PKS 2155-304 and PG 1553+113 obtained from a monoscopic analysis of the CT5 data will be presented. The limitations of the H.E.S.S. II analysis and related systematic uncertainties will be discussed, as well as possible implication for the Cherenkov Telescope Array (CTA).

Speaker: Dr Dmitry Zaborov (C.N.R.S. / LLR)

5 Atmospheric Monitoring for Ground-Based Astroparticle Detectors

Abstract: Ground-based observatories for gamma and cosmic rays make use of the atmosphere as their calorimeter. As with all detectors in particle physics, the processes and interactions within it need to be well understood, and its parameters need to be monitored constantly. The influence of atmospheric state variables on the development of extensive air showers and their secondary light yield (e.g., fluorescence and Cherenkov light) is still a source of large systematic uncertainties for the observatories. The precise monitoring of atmospheric parameters and light transmission without disturbing the observations can be challenging. In this presentation I will discuss the influences of the atmosphere on the measurements of cosmic and gamma rays, as well as the instruments and methods used for its characterization.

Speaker: Dr Martin Will (IAC)

Slides MWill_MPI_2017.pdf

6 Cosmic-ray proton measurements with the Fermi-LAT

on SKYPE Abstract: The Large Area Telescope (LAT) on the Fermi Gamma-ray Space Telescope has continuously observed the gamma-ray sky since June 2008. Cosmic-ray protons represent the majority of events downloaded from the Fermi-LAT, which are removed from the gamma-ray dataset. Our sample is comprised of over 1 billion cosmic-ray protons to TeV energies. We present the measurement of the cosmic-ray proton spectrum between 54 GeV and 9.5 TeV using 7 years of Pass 8 flight data from the Fermi-LAT. We developed a dedicated proton event selection with an acceptance of 0.25 m^2 sr. Our analysis yields a large dataset with low statistical uncertainty and low residual contamination for a spectral measurement. The systematic errors associated with the acceptance, energy measurement, GEANT4 Monte-Carlo simulations are an order of magnitude larger than the statistical uncertainty. The event selection and spectral measurement of the proton analysis create the opportunity for additional proton analyses with the Fermi-LAT, such as a dedicated proton anisotropy search.

Speaker: Dr David Green (GSFC)