Abstracts of Interest
Selected by:
Jose Bellido
Abstract: 1708.04817
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Title: Fermi acceleration under control: $η$ Carinae
(Submitted on 16 Aug 2017)
Abstract: We used data from the Fermi Large Area Telescope obtained during the last 7 years and spanning two passages of $\eta$ Carinae at periastron and compared them with the predictions of particle acceleration in hydrodynamic simulations. Two emission components can be distinguished. The low-energy component cuts off below 10 GeV and its flux, modulated by the orbital motion, varies by a factor less than 2. Short-term variability occurs at periastron. The flux of the high energy component varies by a factor 3-4 but differently during the two periastrons. The variabilities observed at low-energy, including some details of them, and these observed at high-energy during the first half of the observations, do match the prediction of the simulation, assuming a surface magnetic field in the range 0.4-1 kG. The high-energy component and the thermal X-ray emission were weaker than expected around the second periastron suggesting a modification of the wind density in the inner wind collision zone. Diffuse shock acceleration in the complex geometry of the wind collision zone of $\eta$ Carinae provides a convincing match to the observations and new diagnostic tools to probe the geometry and energetics of the system.
Abstract: 1708.04724
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Title: Astrophysical Multimessenger Observatory Network (AMON): Science, Infrastructure, and Status
(Submitted on 16 Aug 2017)
Abstract: The realization of multimessenger astrophysics will open new vistas upon the most energetic events in the universe. Messenger particles of all four of nature's fundamental forces, recorded by detectors on the ground and satellites in space, enable coincidence searches for multimessenger phenomena that will allow us to discover, observe, and explore these sources. The Astrophysical Multimessenger Observatory Network (AMON) links multiple high-energy neutrino, cosmic ray, and gamma-ray observatories as well as gravitational wave facilities into a single virtual system, enabling near real-time coincidence searches for multimessenger astrophysical transients and their electromagnetic counterparts, and providing alerts to follow-up observatories. The science case, design elements, partner observatories, and status of the AMON project are presented, followed by recent results from AMON real-time and archival analyses.
Abstract: 1708.04719
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Title: VERITAS observations of the Cygnus Region
(Submitted on 15 Aug 2017)
Abstract: The Cygnus region of the galaxy is one of the richest regions of gas and star formation and is the brightest region of diffuse GeV emission in the northern sky. VERITAS has conducted deep observations (approximately 300 hours) in the direction of Cygnus region, reaching an average sensitivity of a few percent of the Crab nebula flux. We present the results of these observations and an analysis of over seven years of Fermi-LAT data above 1 GeV. In addition to a search for new sources in the region, we present updated spectra and morphologies of the known TeV gamma-ray sources and a study of their relationship with the GeV emission from the region. These results are discussed in their multiwavelength context including the recently published HAWC observatory gamma-ray catalog. A comparison is also made to the H.E.S.S. galactic plane survey.
Abstract: 1708.04718
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Title: PSR J2032+4127, the counterpart of TeV J2032+4130? Multiwavelength Monitoring of the Approach to Periastron
(Submitted on 15 Aug 2017)
Abstract: PSR J2032+4127 has recently been identified as being in a long period (45-50 years) binary in a highly eccentric orbit with the Be star MT91 213. Periastron is due to occur in November 2017 and this rare occurrence has prompted a multiwavelength monitoring campaign to determine if the system is a gamma-ray binary, and, if so, to study what would be only the second gamma-ray binary with a known compact object. In the same direction as TeV J2032+4130, gamma-ray emission from this binary system could be related to the extended very high energy gamma-ray emission from that region. As part of this monitoring, observations are being conducted by Swift, Fermi-LAT and VERITAS. We present the status of those observations, preliminary results and the plan for continued monitoring through periastron.
Abstract: 1708.04550
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Title: Performance of the upgraded H.E.S.S. cameras
(Submitted on 15 Aug 2017)
Abstract: The 14 years old cameras of the H.E.S.S. 12-m telescopes have been upgraded in 2015/2016, with the goals of reducing the system failure rate, reducing the dead time and improving the overall performance of the array. This conference contribution describes the various tests that were carried out on the cameras and their sub-components both in the lab and on site. It also gives an overview of the commissioning and calibration procedures adopted during and after the installation, including e.g. flat-fielding and trigger threshold scans. Finally, it reports in detail about the overall performance of the four new H.E.S.S. I cameras, using very recent data.
Abstract: 1708.04355
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Title: A First Look at Periodicity in HAWC with TeV Binaries
(Submitted on 14 Aug 2017)
Abstract: Only five binary systems have been found to emit at TeV energies. Each of these systems is composed of a massive O or B type star and a compact object (black hole or a pulsar). The type of compact object and the origin of the gamma-ray emission is unknown for most of these systems. Extending spectral observations to higher energies can help disentangle the nature of the compact object as well as the particle acceleration mechanisms present. Interestingly, the TeV emission from these systems does not always coincide with their emission in GeV or X-ray, which is how many such systems have been originally discovered. Increased coverage of these systems may allow HAWC to see precisely when in the orbit the TeV emission begins and ends. The HAWC Observatory detects TeV gamma-rays with high sensitivity, covering over two-thirds of the overhead sky every day. Applying a stacking method to known TeV binary systems can help HAWC enhance the signal from TeV binaries above the steady background from other sources in the galaxy. We will present results from this stacking analysis using 760 days of HAWC data.
Abstract: 1708.04247
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Title: The total satellite population of the Milky Way
(Submitted on 14 Aug 2017)
Abstract: The total number and luminosity function of the population of dwarf galaxies of the Milky Way (MW) provide important constraints on the nature of the dark matter and on the astrophysics of galaxy formation at low masses. However, only a partial census of this population exists because of the flux limits and restricted sky coverage of existing Galactic surveys. We combine the sample of satellites recently discovered by the Dark Energy Survey (DES) survey with the satellites found in Sloan Digital Sky Survey (SDSS) Data Release 9 (together these surveys cover nearly half the sky) to estimate the total luminosity function of satellites down to $M_{\rm V}=0$. We apply a new Bayesian inference method in which we assume that the radial distribution of satellites follows that of subhaloes selected according to their peak maximum circular velocity. We find that there should be at least $142^{+53}_{-34}$ ($1\sigma$ CL) satellites brighter than $M_{\rm V}=0$ within $300$ kpc of the Sun. As a result of our use of new data and better simulations, and a more robust statistical method, we infer a much smaller population of satellites than reported in previous studies using earlier SDSS data only; we also address an underestimation of the uncertainties in earlier work by accounting for discreteness effects. We find that the inferred number of faint satellites depends only weakly on the assumed mass of the MW halo and we provide scaling relations to extend our results to different assumed halo masses and outer radii. We predict that half of our estimated total satellite population of the MW should be detected by the Large Synoptic Survey Telescope (LSST).
Abstract: 1708.04045
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Title: VHE Observations of Galactic binary systems with VERITAS
(Submitted on 14 Aug 2017)
Abstract: Gamma-ray binaries are variable sources of GeV-to-TeV photons with the peak in their spectral energy distributions above 100 MeV. There are only five Galactic gamma-ray binaries known and the processes which govern particle acceleration, non-thermal emission and the variability patterns are not well understood. We present here for the first time results of the VERITAS binary discovery program at VHE energies and a summary of eleven years of observations of the gamma-ray binary HESS J0632+057. VERITAS has acquired more than 220 hours of observations on HESS J0632+057. The results are discussed in the context of contemporaneous observations with Swift XRT at X-ray energies.
Abstract: 1708.04043
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Title: Highlights of the MAGIC AGN program
(Submitted on 14 Aug 2017)
Abstract: MAGIC is a system of two Cherenkov telescopes designed to perform observations of gamma rays with energies from about 50 GeV to tens of TeV. A low energy threshold and an excellent low energy performance make it a powerful instrument for studies of high energy processes in Active Galactic Nuclei (AGN). The MAGIC Collaboration dedicates about 40% of the telescopes' time to such observations, both monitoring of known emitters, and Target of Opportunity observations of flaring events. In this presentation we will discuss the recent highlights of the MAGIC AGN program. In particular, multi year monitoring of radio galaxies, such as M87, and strong peculiar blazars, such as PG 1553+113, will be presented together with new discoveries based on the Target Of Opportunity program.
Abstract: 1708.04032
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Title: HAWC High Energy Upgrade with a Sparse Outrigger Array
(Submitted on 14 Aug 2017)
Abstract: The High Altitude Water Cherenkov (HAWC) gamma-ray observatory consists of 300 water Cherenkov detectors and has been fully operational since March 2015 in central Mexico. It detects cosmic- and gamma-ray showers in the TeV energy range. For multi-TeV energies, the shower reconstruction and hence the performance of the detector is affected by the partial containment of the showers within the array. To improve the sensitivity at the highest energies, HAWC is being upgraded with an outrigger array. It consists of 350 comparably much smaller water Cherenkov detectors, sparsely distributed around the HAWC main array. It will increase the instrumented area by a factor of 4-5. In this contribution, we will present the current status of the upgrade as well as simulation results on anticipated improvements in the performance of the observatory.
Abstract: 1708.03897
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Title: The Gender Balance of the Australian Space Research Community: A Snapshot from the 16th ASRC, 2016
(Submitted on 13 Aug 2017)
Abstract: In recent years, there has been significant debate and discussion about the glaring gender disparity in the physical sciences. To better understand and address this within the Australian Space Research Community, in 2015 we began the process of keeping a record of the gender balance at the annual Australian Space Research Conference. In addition, we began holding an annual 'Women in Space Research' lunch at that meeting, to discuss the situation, and search for routes by which issues of equity can be addressed, and the situation improved. We present an update based on the 16th Australian Space Research Conference, held at RMIT, Melbourne, in September 2016. As in 2015, male attendees outnumbered female attendees approximately 3:1. However, there was a small shift (~2.3%) in the balance, with female delegates now making up 26.4% of the total, up from 24.1% in 2015. This shift was mirrored in the gender distribution of talks, with 28.9% of all oral presentations being given by women (up from 25.2%). More striking, however, were the changes in the distribution of plenary presentations (44.4% female, up from 22.2%), poster presentations (31.8% female, up from 7.7%), and student awards (33.3% female, up from 12.5%). These changes are encouraging, and will hopefully continue in years to come. The conference organising committee again mirrored the gender balance of the delegates as a whole (27.3 % female vs. 26.4% of delegates), though the program committee was markedly more male-dominated this year than last (82.4% male, against last year's 72.2%). At this year's 'Women in Space Research' lunchtime event, a number of suggestions were made that could help to make future conferences, and the wider community, a more equitable place... --- abstract abridged ---
Abstract: 1708.03732
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Title: Probing Cosmic-ray Propagation with TeV Gamma Rays from the Sun Using the HAWC Observatory
(Submitted on 11 Aug 2017)
Abstract: Cosmic rays in the inner solar system are subject to deflection by both the geomagnetic and interplanetary magnetic fields, and simultaneously interact with the Sun's photosphere resulting in the production of gamma rays. This phenomenon can be studied by observing the deficit ("shadow") in the cosmic ray flux from the direction of the Sun and searching for an excess photon signal above the isotropic background. The High Altitude Water Cherenkov (HAWC) Observatory in Mexico has been taking data on the solar disk at TeV energies since the end of 2014. We present our first efforts to estimate the luminosity of TeV gamma rays from the Sun which can be used to place limits on the production mechanisms, including astrophysical processes and beyond the standard model predictions.
Abstract: 1708.03649
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Title: An algorithm for the reconstruction of neutrino-induced showers in the ANTARES neutrino telescope
(Submitted on 11 Aug 2017)
Abstract: Muons created by $\nu_\mu$ charged current (CC) interactions in the water surrounding the ANTARES neutrino telescope have been almost exclusively used so far in searches for cosmic neutrino sources. Due to their long range, highly energetic muons inducing Cherenkov radiation in the water are reconstructed with dedicated algorithms that allow the determination of the parent neutrino direction with a median angular resolution of about \unit{0.4}{\degree} for an $E^{-2}$ neutrino spectrum. In this paper, an algorithm optimised for accurate reconstruction of energy and direction of shower events in the ANTARES detector is presented. Hadronic showers of electrically charged particles are produced by the disintegration of the nucleus both in CC and neutral current (NC) interactions of neutrinos in water. In addition, electromagnetic showers result from the CC interactions of electron neutrinos while the decay of a tau lepton produced in $\nu_\tau$ CC interactions will in most cases lead to either a hadronic or an electromagnetic shower. A shower can be approximated as a point source of photons. With the presented method, the shower position is reconstructed with a precision of about \unit{1}{\metre}, the neutrino direction is reconstructed with a median angular resolution between \unit{2}{\degree} and \unit{3}{\degree} in the energy range of \SIrange{1}{1000}{TeV}. In this energy interval, the uncertainty on the reconstructed neutrino energy is about \SIrange{5}{10}{\%}. The increase in the detector sensitivity due to the use of additional information from shower events in the searches for a cosmic neutrino flux is also presented.
Abstract: 1708.03585
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Title: New gamma/hadron separation parameters for a neural network for HAWC
(Submitted on 11 Aug 2017 (v1), last revised 15 Aug 2017 (this version, v2))
Abstract: The High-Altitude Water Cherenkov experiment (HAWC) observatory is located 4100 meters above sea level. HAWC is able to detect secondary particles from extensive air showers (EAS) initiated in the interaction of a primary particle (either a gamma or a charged cosmic ray) with the upper atmosphere. Because an overwhelming majority of EAS events are triggered by cosmic rays, background noise suppression plays an important role in the data analysis process of the HAWC observatory. Currently, HAWC uses cuts on two parameters (whose values depend on the spatial distribution and luminosity of an event) to separate gamma-ray events from background hadronic showers. In this work, a search for additional gamma-hadron separation parameters was conducted to improve the efficiency of the HAWC background suppression technique. The best-performing parameters were integrated to a feed-foward Multilayer Perceptron Neural Network (MLP-NN), along with the traditional parameters. Various iterations of MLP-NN's were trained on Monte Carlo data, and tested on Crab data. Preliminary results show that the addition of new parameters can improve the significance of the point source at high-energies (~ TeV), at the expense of slightly worse performance in conventional low-energy bins (~ GeV). Further work is underway to improve the efficiency of the neural network at low energies.
Abstract: 1708.03502
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Title: Measuring High-Energy Spectra with HAWC
(Submitted on 11 Aug 2017)
Abstract: The High-Altitude Water-Cherenkov (HAWC) experiment is a TeV $\gamma$-ray observatory located \unit[4100]{m} above sea level on the Sierra Negra mountain in Puebla, Mexico. The detector consists of 300 water-filled tanks, each instrumented with 4 photomultiplier tubes that utilize the water-Cherenkov technique to detect atmospheric air showers produced by cosmic $\gamma$ rays. Construction of HAWC was completed in March of 2015. The experiment's wide instantaneous field of view (\unit[2]{sr}) and high duty cycle (> 95\%) make it a powerful survey instrument sensitive to pulsars, supernova remnants, and other $\gamma$-ray sources. The mechanisms of particle acceleration at these sources can be studied by analyzing their high-energy spectra. To this end, we have developed an event-by-event energy-reconstruction algorithm using an artificial neural network to estimate energies of primary $\gamma$ rays at HAWC. We will present the details of this technique and its performance as well as the current progress toward using it to measure energy spectra of $\gamma$-ray sources.
Abstract: 1708.03384
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Title: Potential constrains on Lorentz invariance violation from the HAWC TeV gamma-rays
(Submitted on 10 Aug 2017)
Abstract: Astrophysical scenarios provide a unique opportunity to test the possible signatures of Lorentz Invariance Violation (LIV) due to the high energies and the very long distances they involve. An isotropic correction to the photon dispersion relation, by hypothetical Lorentz invariance violation, has a consequence that photons of sufficient energy are unstable and decay very fast. The High Altitude Water Cherenkov (HAWC) observatory is sensitive to gamma-rays in the 100 GeV to 100 TeV energy range, making it a very useful tool to study LIV. In this work we present potential stringent limits for the LIV energy scale at first and second order correction by the potential observations of primary very high energy photons in HAWC energy range.
Abstract: 1708.03137
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Title: Morphological and spectral measurements of 2HWC J1928+177 with HAWC and H.E.S.S
(Submitted on 10 Aug 2017)
Abstract: 2HWC J1928+177 is a source recently discovered at TeV energies in the second HAWC catalog. It is coincident with the Fermi unidentified source 3FGL J1928+1739 and the pulsar PSR J1928+1746, which is 83 kyr old and located at a distance of 5 kpc with an Edot=1.6 x 10$^{36}$ erg/s. 2HWC J1928+177 is not detected by any of the IACTs currently in operation, which puts strong constrains on the morphology and spectrum of the source. There is no sign of shell-like structure in the region at other wavelengths, which in addition to the presence of a pulsar at the center, points to a Pulsar Wind Nebula origin of the TeV emission. We present a dedicated morphological and spectral analysis of the region using HAWC and H.E.S.S. data to unveil the nature of the source and study its properties.
Abstract: 1708.03126
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Title: Observations of the Pulsar Wind Nebula HESS J1825-137 with H.E.S.S. II
(Submitted on 10 Aug 2017)
Abstract: 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.
Abstract: 1708.03023
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Title: Calibration Uncertainty for Advanced LIGO's First and Second Observing Runs
(Submitted on 9 Aug 2017)
Abstract: Calibration of the Advanced LIGO detectors is the quantification of the detectors' response to gravitational waves. Gravitational waves incident on the detectors cause phase shifts in the interferometer laser light which are read out as intensity fluctuations at the detector output. Understanding this detector response to gravitational waves is crucial to producing accurate and precise gravitational wave strain data. Estimates of binary black hole and neutron star parameters and tests of general relativity require well-calibrated data, as miscalibrations will lead to biased results. We describe the method of producing calibration uncertainty estimates for both LIGO detectors in the first and second observing runs.
Abstract: 1708.03005
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Title: Combined Analysis of Cosmic-Ray Anisotropy with IceCube and HAWC
(Submitted on 9 Aug 2017)
Abstract: During the past two decades, experiments in both the northern and southern hemispheres have observed a small but measurable energy-dependent sidereal anisotropy in the arrival direction distribution of Galactic cosmic rays with relative intensities at the level of one per mille. Individually, these measurements are restricted by limited sky coverage, and so the power spectrum of the anisotropy obtained from any one measurement displays a systematic correlation between different multipole modes $C_\ell$. We present the results of a joint analysis of the anisotropy on all angular scales using cosmic-ray data collected during 336 days of operation of the High-Altitude Water Cherenkov (HAWC) Observatory (located at 19$^\circ$ N) and 5 years of data taking from the IceCube Neutrino Observatory (located at 90$^\circ$ S) The results include a combined sky map and an all-sky power spectrum in the overlapping energy range of the two experiments at around 10 TeV. We describe the methods used to combine the IceCube and HAWC data, address the individual detector systematics, and study the region of overlapping field of view between the two observatories.
Abstract: 1708.02960
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Full Text: [ PostScript, PDF]
Title: Measurement of the Iron Spectrum in Cosmic Rays with VERITAS
(Submitted on 9 Aug 2017)
Abstract: The elemental energy spectra of cosmic rays play an important role in understanding their acceleration and propagation. Most current results are obtained either from direct measurements by balloon or satellite detectors, or from indirect measurements by air shower detector arrays on the Earth's surface. Imaging Air Cherenkov Telescopes (IACTs), used primarily for gamma-ray astronomy, can also be used for cosmic-ray physics. They are able to measure Cherenkov light emitted both by heavy nuclei and by secondary particles produced in their air showers, and are thus sensitive to the charge and energy of cosmic ray particles with energies of tens to hundreds of TeV.
A measurement of the energy spectrum of iron nuclei, based on 71 hours of data taken by the VERITAS array of IACTs between 2009 and 2012, will be presented. The energy and other properties of the primary particle are reconstructed using a template-based likelihood fit. The event selection makes use of direct Cherenkov light, which is emitted by the primary particle before starting the air shower. A multivariate method is used to estimate the remaining background. Using these methods, the iron spectrum was measured in the energy range from 20 TeV to 500 TeV.
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