arXiv subjects

J. Hinton

Publications and source records attributed to J. Hinton.

At least 55 records · Page 3Linked to original sources

arXiv2017

Observations of the Pulsar Wind Nebula HESS J1825-137 with H.E.S.S. II

We present a new and deep analysis of the pulsar wind nebula (PWN) HESS\,J1825--137 with a comprehensive data set of almost 400 hours taken with the H.E.S.S. array between 2004 and 2016. The large amount of data, and the inclusion of low-threshold H.E.S.S. II data allows us to include a wide energy range of more than 2.5 orders of magnitude, ranging from 150 GeV up to 70 TeV. We exploit this rich data set to study the morphology and the spectral distributions of various subregions of this largely extended source in more detail. We find that HESS\,J1825--137 is not only the brightest source in that region above 32 TeV, but is also one of the most luminous of all firmly identified pulsar wind nebulae in the Milky Way.

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arXiv2017

EDGE: a code to calculate diffusion of cosmic-ray electrons and their gamma-ray emission

The positron excess measured by PAMELA and AMS can only be explained if there is one or several sources injecting them. Moreover, at the highest energies, it requires the presence of nearby ($\sim$hundreds of parsecs) and middle age (maximum of $\sim$hundreds of kyr) source. Pulsars, as factories of electrons and positrons, are one of the proposed candidates to explain the origin of this excess. To calculate the contribution of these sources to the electron and positron flux at the Earth, we developed EDGE (Electron Diffusion and Gamma rays to the Earth), a code to treat diffusion of electrons and compute their diffusion from a central source with a flexible injection spectrum. We can derive the source's gamma-ray spectrum, spatial extension, the all-electron density in space and the electron and positron flux reaching the Earth. We present in this contribution the fundamentals of the code and study how different parameters affect the gamma-ray spectrum of a source and the electron flux measured at the Earth.

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arXiv2017

First Results of Eta Car Observations with H.E.S.S.II

Eta Carinae (or Eta Car) is a colliding-wind binary that shows non-thermal emission from hard X-rays to high-energy $γ$-rays. The $γ$-ray spectrum exhibits two spectral components, where the high-energy component extends up to 300 GeV. Previous observations of Eta Carinae with the High Energy Stereoscopic System (H.E.S.S.) resulted in upper limits. With the addition of the large 28-m central telescope to the H.E.S.S. array in 2012 the lower bound on the energy range has significantly been reduced. This lowers the energy threshold of the analysis compared to the published results due to the improved instrument sensitivity at energies below 400 GeV. Eta Carinae has been regularly observed in the following years with H.E.S.S. II. Here we report on the first results of Eta Carinae observations, which also cover the periastron passage in 2014 - the time of maximum $γ$-ray emission seen in GeV $γ$-rays with Fermi-LAT.

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arXiv2017

Search for Very High Energy Gamma Rays from the Northern $\textit{Fermi}$ Bubble Region with HAWC

We present a search of very high energy gamma-ray emission from the Northern $\textit{Fermi}$ Bubble region using data collected with the High Altitude Water Cherenkov (HAWC) gamma-ray observatory. The size of the data set is 290 days. No significant excess is observed in the Northern $\textit{Fermi}$ Bubble region, hence upper limits above $1\,\text{TeV}$ are calculated. The upper limits are between $3\times 10^{-7}\,\text{GeV}\, \text{cm}^{-2}\, \text{s}^{-1}\,\text{sr}^{-1}$ and $4\times 10^{-8}\,\text{GeV}\,\text{cm}^{-2}\,\text{s}^{-1}\,\text{sr}^{-1}$. The upper limits disfavor a proton injection spectrum that extends beyond $100\,\text{TeV}$ without being suppressed. They also disfavor a hadronic injection spectrum derived from neutrino measurements.

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arXiv2017

Monte Carlo Performance Studies for the Site Selection of the Cherenkov Telescope Array

The Cherenkov Telescope Array (CTA) represents the next generation of ground-based instruments for very-high-energy (VHE) gamma-ray astronomy, aimed at improving on the sensitivity of current-generation experiments by an order of magnitude and providing coverage over four decades of energy. The current CTA design consists of two arrays of tens of imaging atmospheric Cherenkov telescopes, comprising Small, Medium and Large-Sized Telescopes, with one array located in each of the Northern and Southern Hemispheres. To study the effect of the site choice on the overall \gls{cta} performance and support the site evaluation process, detailed Monte Carlo simulations have been performed. These results show the impact of different site-related attributes such as altitude, night-sky background and local geomagnetic field on CTA performance for the observation of VHE gamma rays.

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arXiv2017

The 2HWC HAWC Observatory Gamma Ray Catalog

We present the first catalog of TeV gamma-ray sources realized with the recently completed High Altitude Water Cherenkov Observatory (HAWC). It is the most sensitive wide field-of-view TeV telescope currently in operation, with a 1-year survey sensitivity of ~5-10% of the flux of the Crab Nebula. With an instantaneous field of view >1.5 sr and >90% duty cycle, it continuously surveys and monitors the sky for gamma ray energies between hundreds GeV and tens of TeV. HAWC is located in Mexico at a latitude of 19 degree North and was completed in March 2015. Here, we present the 2HWC catalog, which is the result of the first source search realized with the complete HAWC detector. Realized with 507 days of data and represents the most sensitive TeV survey to date for such a large fraction of the sky. A total of 39 sources were detected, with an expected contamination of 0.5 due to background fluctuation. Out of these sources, 16 are more than one degree away from any previously reported TeV source. The source list, including the position measurement, spectrum measurement, and uncertainties, is reported. Seven of the detected sources may be associated with pulsar wind nebulae, two with supernova remnants, two with blazars, and the remaining 23 have no firm identification yet.

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arXiv2017

Observation of the Crab Nebula with the HAWC Gamma-Ray Observatory

The Crab Nebula is the brightest TeV gamma-ray source in the sky and has been used for the past 25 years as a reference source in TeV astronomy, for calibration and verification of new TeV instruments. The High Altitude Water Cherenkov Observatory (HAWC), completed in early 2015, has been used to observe the Crab Nebula at high significance across nearly the full spectrum of energies to which HAWC is sensitive. HAWC is unique for its wide field-of-view, nearly 2 sr at any instant, and its high-energy reach, up to 100 TeV. HAWC's sensitivity improves with the gamma-ray energy. Above $\sim$1 TeV the sensitivity is driven by the best background rejection and angular resolution ever achieved for a wide-field ground array. We present a time-integrated analysis of the Crab using 507 live days of HAWC data from 2014 November to 2016 June. The spectrum of the Crab is fit to a function of the form $ϕ(E) = ϕ_0 (E/E_{0})^{-α-β\cdot{\rm{ln}}(E/E_{0})}$. The data is well-fit with values of $α=2.63\pm0.03$, $β=0.15\pm0.03$, and log$_{10}(ϕ_0~{\rm{cm}^2}~{\rm{s}}~{\rm{TeV}})=-12.60\pm0.02$ when $E_{0}$ is fixed at 7 TeV and the fit applies between 1 and 37 TeV. Study of the systematic errors in this HAWC measurement is discussed and estimated to be $\pm$50\% in the photon flux between 1 and 37 TeV. Confirmation of the Crab flux serves to establish the HAWC instrument's sensitivity for surveys of the sky. The HAWC survey will exceed sensitivity of current-generation observatories and open a new view of 2/3 of the sky above 10 TeV.

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arXiv2016

Detailed VHE Studies of the Pulsar Wind Nebula HESS J1825-137

The pulsar wind nebula (PWN) HESS~J1825-137, known to exhibit strong energy dependent morphology, was discovered by HESS in 2005. Powered by the pulsar PSR~B1823-13, the TeV gamma-ray emitting nebula is significantly offset from the pulsar. The asymmetric shape and 21~kyr characteristic age of the pulsar suggest that HESS~J1825-137 is in an evolved state, having possibly already undergone reverse shock interactions from the progenitor supernova. Given its large angular extent, despite its 4~kpc distance, it may have the largest intrinsic size of any TeV PWN so far detected. A rich dataset is currently available with H.E.S.S., including H.E.S.S. II data with a low energy threshold, enabling detailed studies of the source properties and environment. We present new views of the changing nature of the PWN with energy, including maps of the region and spectral studies.

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arXiv2016

Discovery of a variable X-ray counterpart to HESS J1832-093: A new gamma-ray binary?

The TeV gamma-ray point source HESSJ1832-093 remains unidentified despite extensive multi-wavelength studies. The gamma-ray emission could originate in a very compact pulsar wind nebula or an X-ray binary system composed of the X-ray source XMMU J183245-0921539 and a companion star (2MASS J18324516-0921545). To unveil the nature of XMMUJ183245-0921539 and its relation to HESSJ1832-093, we performed deeper follow-up observations in X-rays with Chandra and Swift to improve source localisation and to investigate time variability. We observed an increase of the X-ray flux by a factor ~6 in the Chandra data compared to previous observations. The source is point-like for Chandra and its updated position is only 0.3" offset from 2MASS J18324516-0921545, confirming the association with this infrared source. Subsequent Swift ToO observations resulted in a lower flux, again compatible with the one previously measured with XMM-Newton, indicating a variability timescale of the order of two months or shorter. The now established association of XMMU J183245-0921539 and 2MASS J18324516-0921545 and the observed variability in X-rays are strong evidence for binary nature of HESS J1832-093. Further observations to characterise the optical counterpart as well as to search for orbital periodicity are needed to confirm this scenario.

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arXiv2015

The first GCT camera for the Cherenkov Telescope Array

The Gamma Cherenkov Telescope (GCT) is proposed to be part of the Small Size Telescope (SST) array of the Cherenkov Telescope Array (CTA). The GCT dual-mirror optical design allows the use of a compact camera of diameter roughly 0.4 m. The curved focal plane is equipped with 2048 pixels of ~0.2° angular size, resulting in a field of view of ~9°. The GCT camera is designed to record the flashes of Cherenkov light from electromagnetic cascades, which last only a few tens of nanoseconds. Modules based on custom ASICs provide the required fast electronics, facilitating sampling and digitisation as well as first level of triggering. The first GCT camera prototype is currently being commissioned in the UK. On-telescope tests are planned later this year. Here we give a detailed description of the camera prototype and present recent progress with testing and commissioning.

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arXiv2015

Monte Carlo Performance Studies of Candidate Sites for the Cherenkov Telescope Array

The Cherenkov Telescope Array (CTA) is the next-generation gamma-ray observatory with sensitivity in the energy range from 20 GeV to beyond 300 TeV. CTA is proposed to consist of two arrays of 40-100 imaging atmospheric Cherenkov telescopes, with one site located in each of the Northern and Southern Hemispheres. The evaluation process for the candidate sites for CTA is supported by detailed Monte Carlo simulations, which take different attributes like site altitude and geomagnetic field configuration into account. In this contribution we present the comparison of the sensitivity and performance of the different CTA site candidates for the measurement of very-high energy gamma rays.

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arXiv2015

Second large-scale Monte Carlo study for the Cherenkov Telescope Array

The Cherenkov Telescope Array (CTA) represents the next generation of ground based instruments for Very High Energy gamma-ray astronomy. It is expected to improve on the sensitivity of current instruments by an order of magnitude and provide energy coverage from 20 GeV to more than 200 TeV. In order to achieve these ambitious goals Monte Carlo (MC) simulations play a crucial role, guiding the design of CTA. Here, results of the second large-scale MC production are reported, providing a realistic estimation of feasible array candidates for both Northern and Sourthern Hemisphere sites performance, placing CTA capabilities into the context of the current generation of High Energy $γ$-ray detectors.

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arXiv2013

The Real-Time Analysis of the Cherenkov Telescope Array Observatory

The Cherenkov Telescope Array (CTA) Observatory must be capable of issuing fast alerts on variable and transient sources to maximize the scientific return. This will be accomplished by means of a Real-Time Analysis (RTA) pipeline, a key system of the CTA observatory. The latency and sensitivity requirements of the alarm system impose a challenge because of the large foreseen data flow rate, between 0.5 and 8 GB/s. As a consequence, substantial efforts toward the optimization of this high-throughput computing service are envisaged, with the additional constraint that the RTA should be performed on-site (as part of the auxiliary infrastructure of the telescopes). In this work, the functional design of the RTA pipeline is presented.

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arXiv2013

The dual-mirror Small Size Telescope for the Cherenkov Telescope Array

In this paper, the development of the dual mirror Small Size Telescopes (SST) for the Cherenkov Telescope Array (CTA) is reviewed. Up to 70 SST, with a primary mirror diameter of 4 m, will be produced and installed at the CTA southern site. These will allow investigation of the gamma-ray sky at the highest energies accessible to CTA, in the range from about 1 TeV to 300 TeV. The telescope presented in this contribution is characterized by two major innovations: the use of a dual mirror Schwarzschild-Couder configuration and of an innovative camera using as sensors either multi-anode photomultipliers (MAPM) or silicon photomultipliers (SiPM). The reduced plate-scale of the telescope, achieved with the dual-mirror optics, allows the camera to be compact (40 cm in diameter), and low-cost. The camera, which has about 2000 pixels of size 6x6 mm^2, covers a field of view of 10°. The dual mirror telescopes and their cameras are being developed by three consortia, ASTRI (Astrofisica con Specchi a Tecnologia Replicante Italiana, Italy/INAF), GATE (Gamma-ray Telescope Elements, France/Paris Observ.) and CHEC (Compact High Energy Camera, universities in UK, US and Japan) which are merging their efforts in order to finalize an end-to-end design that will be constructed for CTA. A number of prototype structures and cameras are being developed in order to investigate various alternative designs. In this contribution, these designs are presented, along with the technological solutions under study.

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arXiv2013

A Compact High Energy Camera for the Cherenkov Telescope Array

The Compact High Energy Camera (CHEC) is a camera-development project involving UK, US, Japanese and Dutch institutes for the dual-mirror Small-Sized Telescopes (SST-2M) of the Cherenkov Telescope Array (CTA). Two CHEC prototypes, based on different photosensors are funded and will be assembled and tested in the UK over the next ~18 months. CHEC is designed to record flashes of Cherenkov light lasting from a few to a hundred nanoseconds, with typical RMS image width and length of ~0.2 x 1.0 degrees, and has a 9 degree field of view. The physical camera geometry is dictated by the telescope optics: a curved focal surface with radius of curvature 1m and diameter ~35cm is required. CHEC is designed to work with both the ASTRI and GATE SST-2M telescope structures and will include an internal LED flasher system for calibration. The first CHEC prototype will be based on multi-anode photomultipliers (MAPMs) and the second on silicon photomultipliers (SiPMs or MPPCs). The first prototype will soon be installed on the ASTRI SST-2M prototype structure on Mt. Etna.

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arXiv2012

Surveys with the Cherenkov Telescope Array

Surveys open up unbiased discovery space and generate legacy datasets of long-lasting value. One of the goals of imaging arrays of Cherenkov telescopes like CTA is to survey areas of the sky for faint very high energy gamma-ray (VHE) sources, especially sources that would not have drawn attention were it not for their VHE emission (e.g. the Galactic "dark accelerators"). More than half the currently known VHE sources are to be found in the Galactic plane. Using standard techniques, CTA can carry out a survey of the region |l|<60 degrees, |b|<2 degrees in 250 hr (1/4th the available time per year at one location) down to a uniform sensitivity of 3 mCrab (a "Galactic Plane survey"). CTA could also survey 1/4th of the sky down to a sensitivity of 20 mCrab in 370 hr of observing time (an "all-sky survey"), which complements well the surveys by the Fermi/LAT at lower energies and extended air shower arrays at higher energies. Observations in (non-standard) divergent pointing mode may shorten the "all-sky survey" time to about 100 hr with no loss in survey sensitivity. We present the scientific rationale for these surveys, their place in the multi-wavelength context, their possible impact and their feasibility. We find that the Galactic Plane survey has the potential to detect hundreds of sources. Implementing such a survey should be a major goal of CTA. Additionally, about a dozen blazars, or counterparts to Fermi/LAT sources, are expected to be detected by the all-sky survey, whose prime motivation is the search for extragalactic "dark accelerators".

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arXiv2009

Probing the Nature of the unidentified TeV Gamma-ray source HESS J0632+057 with Swift

New generation TeV gamma-ray telescopes have discovered many new sources, including several enigmatic unidentified TeV objects. HESS J0632+057 is a particularly interesting unidentified TeV source since: it is a point source, it has a possible hard-spectrum X-ray counterpart and a positionally consistent Be star, it has evidence of long-term VHE flux variability, and it is postulated to be a newly detected TeV/X-ray binary. We have obtained Swift X-ray telescope observations of this source from MJD 54857 to 54965, in an attempt to ascertain its nature and to investigate the hypothesis that it's a previously unknown X-ray/TeV binary. Variability and spectral properties similar to those of the other 3 known X-ray/TeV binaries have been observed, with measured flux increases by factors of approximately 3. X-ray variability is present on multiple timescales including days to months; however, no clear signature of periodicity is present on the timescales probed by these data. If binary modulation is present and dominating the measured variability, then the period of the orbit is likely to be more than 54 days (half of this campaign), or it has a shorter period with a variable degree of flux modulation on successive high states. If the two high states measured to date are due to binary modulation, then the favored period is approximately 35-40 days. More observations are required to determine if this object is truly a binary system and to determine the extent that the measured variability is due to inter-orbit flaring effects or periodic binary modulation.

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arXiv2007

VHE gamma-rays from Westerlund 2 and implications for the inferred energetics

The H.E.S.S. collaboration recently reported the discovery of VHE gamma-ray emission coincident with the young stellar cluster Westerlund 2. This system is known to host a population of hot, massive stars, and, most particularly, the WR binary WR20a. Particle acceleration to TeV energies in Westerlund 2 can be accomplished in several alternative scenarios, therefore we only discuss energetic constraints based on the total available kinetic energy in the system, the actual mass loss rates of respective cluster members, and implied gamma-ray production from processes such as inverse Compton scattering or neutral pion decay. From the inferred gamma-ray luminosity of the order of 10^35 erg/s, implications for the efficiency of converting available kinetic energy into non-thermal radiation associated with stellar winds in the Westerlund 2 cluster are discussed under consideration of either the presence or absence of wind clumping.

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