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Segev BenZvi

Publications and source records attributed to Segev BenZvi.

44 records · Page 3Linked to original sources
arXiv2017

Limits on the Emission of Gamma Rays from M31 (The Andromeda Galaxy) with HAWC

The detection of the Fermi Bubbles suggests that spiral galaxies such as the Milky Way can undergo active periods. Using gamma-ray observations, we can investigate the possibility that such structures are present in other nearby galaxies. We have analyzed the region around the Andromeda Galaxy (Messier Catalog M31) for signs of bubble-like emission using TeV gamma-ray data recorded by the High-Altitude Water Cherenkov Observatory. We fit a model consisting of two 6 kpc bubbles symmetric about and perpendicular to the M31 galactic plane and assume a power-law distribution for the gamma-ray flux. We compare the emission from these bubble regions to that expected from structures similar to the Fermi Bubbles found in the Milky Way. No significant emission was observed. We report upper limits on the TeV flux from Fermi Bubble structures in M31.

astro-ph.HE↗
arXiv2017

Observation of Galactic Cosmic Rays and Gamma Rays with the High Altitude Water Cherenkov Observatory

The High-Altitude Water Cherenkov Observatory, or HAWC, is carrying out an unbiased survey of cosmic rays and gamma rays from the Northern Hemisphere between 100 GeV and 100 TeV. HAWC is currently the only high-uptime wide-field TeV observatory in operation, and has a robust program to search for flares and other transient sources of gamma rays. The detector is also well suited to observe spatially extended regions of gamma-ray emission and cosmic-ray anisotropy. HAWC recently concluded its first year of data taking with the complete detector. The results include not only observations of many known TeV point sources, but also extended emission from Galactic objects like the Geminga supernova remnant. These results have implications for the origins of several astrophysical anomalies observed in the cosmic-ray data, such as the excess of Galactic positrons at Earth. We will describe results from HAWC with a focus on the observation of cosmic rays and Galactic sources of gamma rays.

astro-ph.HE↗
arXiv2016

FemtoDAQ: A Low-Cost Digitizer for SiPM-Based Detector Studies and its Application to the HAWC Detector Upgrade

The FemtoDAQ is a low-cost two channel data acquisition system which we have used to investigate the signal characteristics of silicon photomultipliers (SiPMs) coupled to fast scintillators. The FemtoDAQ system can also be used to instrument low cost moderate performance passive detectors, and is suitable for use in harsh environments (e.g., high altitude). The FemtoDAQ is being used as a SiPM test bench for the High Altitude Water Cherenkov (HAWC) Observatory, a TeV gamma ray detector located 4100 m above sea level. Planned upgrades to the HAWC array can benefit greatly from SiPMs, a robust, low-voltage, low-cost alternative to traditional vacuum photomultipliers. The FemtoDAQ is used to power the SiPM detector front end, bias the SiPM, and digitize the photosensor output in a single compact unit.

astro-ph.IM↗
arXiv2015

Towards a Measurement of the $e^+e^-$ Flux above 1 TeV with HAWC

The High-Altitude Water Cherenkov (HAWC) Observatory records the air showers produced by cosmic rays and gamma rays at a rate of about 20 kHz. While the events observed by HAWC are 99.9% hadronic cosmic rays, this background can be strongly suppressed using topological cuts that preferentially select electromagnetic air showers. Using this capability of HAWC, we can create a sample of air showers dominated by gamma rays and cosmic electrons and positrons. HAWC is one of the few operating observatories capable of measuring showers produced by electron and positron primaries above 1 TeV, and can record these showers from two-thirds of the sky each day. We describe the sensitivity of HAWC to leptonic cosmic rays, and discuss prospects for the measurement of the combined $e^+e^-$ flux and possible approaches for positron and electron charge separation with the HAWC detector.

astro-ph.HE↗
arXiv2015

Looking for Gamma-ray Emission from TeV Binary Candidates with HAWC

The Milky Way contains hundreds of binary systems which are known to emit in radio and X-rays, but only a handful of binaries have been observed to produce very high-energy gamma rays. In addition, the emission mechanisms which produce the gamma rays in the few known sources are not well understood. To improve the statistics of binary sources in the TeV band, the High-Altitude Water Cherenkov Gamma-ray Observatory, or HAWC, has begun to carry out a simultaneous survey of TeV binary candidates in the Northern Hemisphere between 100 GeV and 100 TeV. HAWC is a surface array that records air showers from cosmic rays and gamma rays with a high uptime and wide field of view, making it well-suited to observe time-dependent emission from objects such as TeV binaries. We describe the sensitivity of HAWC to periodic emission from Galactic sources of gamma rays and present data from the first year of observations with the partially constructed observatory.

astro-ph.HE↗
arXiv2007

New method for atmospheric calibration at the Pierre Auger Observatory using FRAM, a robotic astronomical telescope

FRAM - F/(Ph)otometric Robotic Atmospheric Monitor is the latest addition to the atmospheric monitoring instruments of the Pierre Auger Observatory. An optical telescope equipped with CCD camera and photometer, it automatically observes a set of selected standard stars and a calibrated terrestrial source. Primarily, the wavelength dependence of the attenuation is derived and the comparison between its vertical values (for stars) and horizontal values (for the terrestrial source) is made. Further, the integral vertical aerosol optical depth can be obtained. A secondary program of the instrument, the detection of optical counterparts of gamma-ray bursts, has already proven successful. The hardware setup, software system, data taking procedures, and first analysis results are described in this paper.

astro-ph↗
arXiv2003

Conceptual Design of a Cosmic Ray Detector Operating Between 10^17 and 10^19 eV for the Study of the Galactic Center

For our understanding of the origin of ultra high energy cosmic rays, the energy region between 10^17 and 10^19 eV is of crucial importance. Previous experiments have found indirect evidence that at these energies, the origin of cosmic rays changes from predominantly Galactic to extragalactic. In addition, weak evidence for an excess of cosmic rays from the direction of the Galactic center in a narrow energy band around 10^18 eV has been claimed. However, so far there is no direct evidence supporting this scenario. Neither Galactic nor extragalactic sources have been unambiguously established. Given the importance of this energy range, there is a strong case for a dedicated experiment to study the EeV energy region with high precision. We present the conceptual design of GRaNDScan, a mobile stereo air fluorescence detector optimized to study the spectrum, composition, and arrival direction of cosmic rays in this important energy range. If located at a site on the southern hemisphere with good exposure to the Galactic center, this type of experiment will provide an accurate map of the Galactic center region, long suspected to harbor one or several sources of ultra high energy cosmic rays.

astro-ph↗