Amanda Weinstein

Recent Observations of Supernova Remnants with VERITAS

Supernova remnants (SNRs) are widely considered the most likely source of cosmic rays below the knee (10 15 eV). Studies of GeV and TeV gamma-ray emission in the vicinity of SNRs, in combination with multi-wavelength observations, can trace and constrain the nature of the charged particle population believed to be accelerated within SNR shocks. They may also speak to the diffusion and propagation of these energetic particles and to the nature of the acceler- ation mechanisms involved. We report here on recent observations of SNRs with VERITAS, including the discoveries of VHE gamma-ray emission from from G120.1+1.4 (Tychos SNR) and from the northwest shell of G78.2+2.1 (gamma-ray source VER J2019+407, which was discovered as a consequence of the VERITAS Cygnus region survey).

An image-based array trigger for imaging atmospheric Cherenkov telescope arrays

Abstract It is anticipated that forthcoming, next generation, atmospheric Cherenkov telescope arrays will include a number of medium-sized telescopes that are constructed using a dual-mirror Schwarzschild–Couder configuration. These telescopes will sample a wide ( 8 ° ) field of view using a densely pixelated camera comprising over 1 0 4 individual readout channels. A readout frequency congruent with the expected single-telescope trigger rates would result in substantial data rates. To ameliorate these data rates, a novel, hardware-level Distributed Intelligent Array Trigger (DIAT) is envisioned. A copy of the DIAT operates autonomously at each telescope and uses reduced resolution imaging data from a limited subset of nearby telescopes to veto events prior to camera readout and any subsequent network transmission of camera data that is required for centralized storage or aggregation. We present the results of Monte-Carlo simulations that evaluate the efficacy of a “Parallax width” discriminator that can be used by the DIAT to efficiently distinguish between genuine gamma-ray initiated events and unwanted background events that are initiated by hadronic cosmic rays.

Creating a high-resolution picture of Cygnus with the Cherenkov Telescope Array

The Cygnus region hosts one of the most remarkable star-forming regions in the Milky Way. Indeed, the total mass in molecular gas of the Cygnus X complex exceeds 10 times the total mass of all other nearby star-forming regions. Surveys at all wavelengths, from radio to gamma-rays, reveal that Cygnus contains such a wealth and variety of sources---supernova remnants (SNRs), pulsars, pulsar wind nebulae (PWNe), H II regions, Wolf-Rayet binaries, OB associations, microquasars, dense molecular clouds and superbubbles---as to practically be a galaxy in microcosm. The gamma-ray observations along reveal a wealth of intriguing sources at energies between 1 GeV and tens of TeV. However, a complete understanding of the physical phenomena producing this gamma-ray emission first requires us to disentangle overlapping sources and reconcile discordant pictures at different energies. This task is made more challenging by the limited angular resolution of instruments such as the Fermi Large Area Telescope, ARGO-YBJ, and HAWC and the limited sensitivity and field of view of current imaging atmospheric Cherenkov telescopes (IACTs). The Cherenkov Telescope Array (CTA), with its improved angular resolution, large field of view, and order of magnitude gain in sensitivity over current IACTs, has the potential to finally create a coherent and well-resolved picture of the Cygnus region between a few tens of GeV and a hundred TeV. We describe a proposed strategy to study the Cygnus region using CTA data, which combines a survey of the whole region at

Status of the array control and data acquisition system for the Cherenkov Telescope Array

65^{\circ} < l < 85^{\circ}

Towards a global software architecture for operating and controlling the Cherenkov Telescope Array

and

Commissioning and performance of a fast level-2 trigger system at VERITAS

-3.5^{\circ} < b < 3.5^{\circ}

The fluid database paradigm: a prototype

with deeper observations of two sub-regions that host rich groups of known gamma-ray sources.

The topological trigger system for the VERITAS upgrade

The Cherenkov Telescope Array (CTA) will be the next-generation ground-based observatory using the atmospheric Cherenkov technique. The CTA instrument will allow researchers to explore the gamma-ray sky in the energy range from 20 GeV to 300 TeV. CTA will comprise two arrays of telescopes, one with about 100 telescopes in the Southern hemisphere and another smaller array of telescopes in the North. CTA poses novel challenges in the field of ground-based Cherenkov astronomy, due to the demands of operating an observatory composed of a large and distributed system with the needed robustness and reliability that characterize an observatory. The array control and data acquisition system of CTA (ACTL) provides the means to control, readout and monitor the telescopes and equipment of the CTA arrays. The ACTL system must be flexible and reliable enough to permit the simultaneous and automatic control of multiple sub-arrays of telescopes with a minimum effort of the personnel on-site. In addition, the system must be able to react to external factors such as changing weather conditions and loss of telescopes and, on short timescales, to incoming scientific alerts from time-critical transient phenomena. The ACTL system provides the means to time-stamp, readout, filter and store the scientific data at aggregated rates of a few GB/s. Monitoring information from tens of thousands of hardware elements need to be channeled to high performance database systems and will be used to identify potential problems in the instrumentation. This contribution provides an overview of the ACTL system and a status report of the ACTL project within CTA.

The VERITAS Survey of the Cygnus Region of the Galactic Plane

The Cherenkov Telescope Array (CTA) is an international initiative to build the next generation ground-based gamma-ray instrument. CTA will allow studying the Universe in the very-high-energy gamma-ray domain with energies ranging from a few tens of GeV to more than a hundred TeV. It will extend the currently accessible energy band, while increasing the sensitivity by a factor of 10 with respect to existing Cherenkov facilities. Furthermore, CTA will enhance other important aspects like angular and energy resolution. CTA will comprise two arrays, one in the Northern hemisphere and one in the Southern hemisphere, of in total more than one hundred of telescopes of three different sizes. The CTA performance requirements and the increased complexity in operation, control and monitoring of such a large distributed multi-telescope array leads to new challenges in designing and developing the CTA control software system. Indeed, the control software system must be flexible enough to allow for the simultaneous operation of multiple sub-arrays of different types of telescopes, to be ready to react in short timescales to changing weather conditions or to automatic alarms for transient phenomena, to be able to operate the observatory with a minimum personal effort on site, to cope with the malfunctioning of single telescopes or sub-arrays of telescopes, and to readout and control a large and heterogeneous set of devices. This report describes the preliminary architectural design concept for the CTA control software system that will be responsible to manage all the functionality of the CTA array, thereby enabling CTA to reach its scientific goals.

Simulations of a Distributed Intelligent Array Trigger for the Cherenkov Telescope Array

We have built a new three-stage FPGA-based high-speed trigger for VERITAS, an array of ground-based imaging atmospheric Cherenkov telescopes (IACTs) located in Arizona. This trigger has the ability to recognize patterns of Cherenkov light generated by atmospheric air showers initiated by incident extra-terrestrial gamma rays. The new trigger has programmable coincidence recognition timing and programmable delay compensation over 499 pixel channels in an IACT camera. Measurement of and compensation for systemic variations is achieved through the use of an FPGA-based time-to-digital converter (TDC) and FPGA-based programmable delay elements. The trigger pattern is the coincidence of any three adjacent pixels within the camera. The minimum coincidence window of 3ns with low dead time provides sensitivity at lower energies than were achieved previously. The new trigger has now been successfully installed on all four of the IACTs of VERITAS, replacing the previous system. We present measurements of the performance of this new trigger in comparison with that of the previous system and of the effect of the new trigger upon overall array performance.