H.E.S.S. searches for TeV gamma rays associated to high-energy neutrinos
Fabian Schüssler, Halim Ashkar, Michael Backes, Kathrin Egberts, Francois Brun, Matthias Füßling, Clemens Hoischen, Jean-Philippe Lenain, Iryna Lypova, Stefan O… 展开作者
Fabian Schüssler, Halim Ashkar, Michael Backes, Kathrin Egberts, Francois Brun, Matthias Füßling, Clemens Hoischen, Jean-Philippe Lenain, Iryna Lypova, Stefan Ohm, Dan Parsons, Carlo Romoli, Monica Seglar-Arroyo, Michael Zacharias, Andreas Zech
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Proceedings of the 36th International Cosmic Ray Conference, 2019, Madison, WI, USA
The detection of an astrophysical flux of high-energy neutrinos by IceCube is a major step forward in the search for the origin of cosmic rays, as this emission is expected to originate in hadronic interactions taking place in or near cosmic-ray accelerators. No neutrino point sources, or significant correlation with known astrophysical objects, have been identified in the IceCube data so far. The hadronic interactions responsible for the neutrino emission should also lead to the production of high-energy gamma rays. The search for neutrino sources can then be performed by studying the spatial and temporal correlations between neutrino events and very high energy (VHE, E > 100 GeV) gamma rays. We report here on the search for VHE gamma-ray emission with the H.E.S.S. imaging air Cherenkov telescopes (IACTs) at the reconstructed position of muon neutrino events detected by IceCube. We will provide an up-to-date summary of the extensive program to perform prompt IACT observations of realtime IceCube neutrino event positions. A recent highlight of this program are the H.E.S.S. observations during the broad multi-wavelength campaign that followed the detection of the neutrino event IceCube-170922A arriving from a direction consistent with the location of a flaring gamma-ray blazar TXS 0506+056 in September 2017. We'll present the H.E.S.S. observations obtained within ~4h hours of the neutrino detection as well as a complementary search for gamma-ray emission at longer timescales and put them into the multi-wavelength and multi-messenger context.
Pulsars are known to be efficient accelerators that produce copious amounts of relativistic particles and inject them into the Galactic medium. The radiation emitted by such a pulsar wind can be seen from radio through gamma-rays as a pulsar-wind nebula (PWN). Here we overview and summarize recent progress in X-ray and TeV observations of PWNe.
Dark matter candidates such as weakly-interacting massive particles are predicted to annihilate or decay into Standard Model particles leaving behind distinctive signatures in gamma rays, neutrinos, positrons, antiprotons, or even anti-nuclei. Indirect dark matter searches, and in particular those based on gamma-ray observations and cosmic ray measurements could detect such signatures. Here we review the strengths and limitations of this approach and look into the future of indirect dark matter searches.
The possibility of estimating the mass composition of primary cosmic rays above the knee of its energy spectrum through the study of high energy gamma rays, muons and neutrinos produced in the interactions of cosmic rays with the solar ambient matter and radiation has been explored. It is found that the theoretical fluxes of TeV gamma rays, muons and neutrinos from a region around $15^{o}$ of the Sun are sensitive to mass composition of cosmic rays in the PeV energy range. The experimental prospects for detection of such TeV gamma rays/neutrinos by future experiments are discussed.
TeV gamma-rays have been observed from blazars as well as from radio galaxies like M87 and Cen A. In leptonic models, gamma-rays above the pair production threshold can escape from the ultra-relativistic jet, since large Lorentz factors reduce the background photon densities compared to those required for isotropic emission. Here we discuss an alternative scenario, where VHE photons are generated as secondaries from UHECR interaction in the AGN core. We show that TeV gamma-rays can escape from the core despite large IR and UV backgrounds. For the special case of Cen A, we study if the various …
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 th…
The HAWC observatory is an air-shower detector, which is designed to study both astrophysical gamma-rays in the TeV region and galactic cosmic rays in the energy interval from 1 TeV to 1 PeV. This energy regime is quite interesting for cosmic ray research, since indirect observations overlap with direct measurements, which offers the opportunity for cross calibration and studies of experimental systematic errors in both techniques. One quantity that could help for this purpose is the all-particle energy spectrum of cosmic rays. In this work, we present an update of HAWC measurements on the tot…
Between May 2009 and May 2010, the IceCube neutrino detector recorded 32 billion of atmospheric muons generated in air showers produced by cosmic rays in the TeV energy range. With such high statistics sample it is possible to observe, for the first time in the southern hemisphere, an energy dependence in the Galactic cosmic ray anisotropy up to a few hundred TeV. This study shows that the same large-scale anisotropy observed at median energies around 20 TeV is not present at 400 TeV; the anisotropy observed at 400 TeV shows substantial differences with respect to that at lower energy. In addi…
The High-Altitude Water Cherenkov (HAWC) Observatory, located 4100 m above sea level near Sierra Negra (19$^\circ$ N) in Mexico, is sensitive to gamma rays and cosmic rays at TeV energies. The arrival direction distribution of cosmic rays at these energies shows significant anisotropy on several angular scales, with a relative intensity ranging between 10$^{-3}$ and 10$^{-4}$. We present the results of a study of cosmic-ray anisotropy based on more than 86 billion cosmic-ray air showers recorded with HAWC since June 2013. The HAWC cosmic-ray sky map, which has a median energy of 2 TeV, exhibit…
We present a measurement of the energy spectrum of the light mass group of cosmic rays (protons and helium) with the High Altitude Water Cherenkov (HAWC) Observatory in the energy interval from $10$ TeV to $200$ TeV. The spectrum covers the energy range between direct and indirect measurements, where precision data on the composition of cosmic rays are needed. The spectrum was constructed by applying an unfolding technique on a proton plus helium enriched sub-sample ($>90\%$ abundance) of cosmic ray air showers selected from the HAWC cosmic-ray data. The subset contains $3.8 \times 10^{9}$ air…
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 showe…
Cosmic ray interactions that produce high-energy neutrinos also inevitably generate high-energy gamma rays, which finally contribute to the diffuse high-energy gamma-ray background after they escape the sources. It was recently found that, the high flux of neutrinos at $\sim30$ TeV detected by IceCube lead to a cumulative gamma-ray flux exceeding the Fermi isotropic gamma-ray background at 10-100 GeV, implying that the neutrinos are produced by hidden sources of cosmic rays, where GeV-TeV gamma-rays are not transparent. Here we suggest that relativistic jets in tidal disruption events (TDEs) o…
GRIPS is planned to be the next great satellite-born survey mission lead by Europe; it will look into the cosmos with unprecedented accuracy in several bands of the EM spectrum (infrared, X-rays, MeV gamma-rays); in particular in gamma-rays, GRIPS will be able to bridge the so-called MeV gap and to answer several questions brought forth by GeV-TeV gamma-ray observations. We will discuss here several connections to GeV-TeV gamma-ray astrophysics, focussing in particular to show how GRIPS will be crucial in revealing the origin of cosmic rays.
Cosmic rays are a sample of solar, galactic and extragalactic matter. Their origin and properties are one of the most intriguing question in modern astrophysics. The most energetic events and active objects in the Universe: supernovae explosion, pulsars, relativistic jets, active galactic nuclei, have been proposed as sources of cosmic rays although unambiguous evidences have still to be found. Electrons, while comprising ~1% of the cosmic radiation, have unique features providing important information regarding the origin and propagation of cosmic rays in the Galaxy that is not accessible fro…
We will present the multi-wavelength modeling of the supernova remnant Cassiopeia A's shell based on radio, X-rays, and GeV-TeV gamma rays. Our aim is to estimate the location of TeV gamma rays with the help of spectral analysis of X-rays from different regions of the shell, because Chandra X-ray observations have a far better angular resolution than the gamma-ray measurements. Our analysis shows X-ray flux levels from various regions of the remnant to be different. We find that leptonic model is unable to explain the GeV and TeV data, simultaneously. So, we invoke a hadronic model as an addit…
A thorough search for large scale anisotropies in the distribution of arrival directions of cosmic rays detected above $10^{18}$ eV at the Pierre Auger Observatory is reported. For the first time, these large scale anisotropy searches are performed as a function of both the right ascension and the declination and expressed in terms of dipole and quadrupole moments. Within the systematic uncertainties, no significant deviation from isotropy is revealed. Upper limits on dipole and quadrupole amplitudes are derived under the hypothesis that any cosmic ray anisotropy is dominated by such moments i…
We consider the neutron star (NS) of the magnetar type inside the massive binary system. We determine the conditions under which the matter from the stellar wind can penetrate the inner magnetosphere of the magnetar. At some distance from the NS surface, the magnetic pressure can balance the gravitational pressure of the accreting matter creating very turbulent, magnetized transition region. It is suggested that this region provides good conditions for acceleration of electrons to relativistic energies. These electrons lose energy on the synchrotron process and the Inverse Compton (IC) scatter…
Carpet is an air-shower array at Baksan, Russia, equipped with a large-area muon detector, which makes it possible to separate primary photons from hadrons. We report first results of the search for primary photons with energies E>100 TeV. The experiment's ongoing upgrade and future sensitivity are also discussed.
Particle acceleration in the inner ~ 200 pc of the Galaxy is discussed, where diffuse TeV gamma-rays have been detected by the High Energy Stereoscopic System (HESS) observation. The diffuse gamma-ray emission has a strong correlation with molecular clouds with large velocity dispersion, indicating the presence of turbulence. It is argued that the turbulence may contribute to the acceleration of cosmic rays via stochastic acceleration. The stochastic acceleration may energize cosmic-ray protons up to ~ 100 TeV and electrons to ~ 1 TeV in a relatively tenuous medium. The difference in the effic…
We present a detailed morphological study of TeV gamma rays, synchrotron radiation, and interstellar gas in the young Type Ia supernova remnant (SNR) RCW 86. We find that the interstellar atomic gas shows good spatial correlation with the gamma rays, indicating that the TeV gamma rays from RCW 86 are likely to be dominantly of hadronic origin. In contrast, the spatial correlation between the interstellar molecular cloud and the TeV gamma rays is poor in the southeastern shell of the SNR. We argue that this poor correlation can be attributed to the low-energy cosmic rays (~ 1 TeV) not penetrati…
Centaurus A (Cen A) is the nearest radio-loud AGN and is detected from radio to very high energy gamma-rays. Its nuclear spectral energy distribution (SED) shows a double-peak feature, which is well explained by the leptonic synchrotron + synchrotron self-Compton model. This model however cannot account for the observed high energy photons in the TeV range, which display a distinct component. Here we show that ~ TeV photons can be well interpreted as the neutral pion decay products from p-gamma interactions of Fermi accelerated high energy protons in the jet with the seed photons around the se…
The IceCube neutrino discovery presents an opportunity to answer long-standing questions in high-energy astrophysics. For their own sake and relations to other processes, it is important to understand neutrinos arising from the Milky Way, which should have an accompanying flux of gamma rays. Examining Fermi TeV data, and applying other constraints up to >1 PeV, it appears implausible that the Galactic fraction of the IceCube flux is large, though could be present at some level. We address Sgr A*, where the TeV-PeV neutrinos may outrun gamma rays due to gamma-gamma opacity, and further implicat…
At TeV energies, the gamma-ray horizon of the universe is limited to redshifts z<<1, and, therefore, any observation of TeV radiation from a source located beyond z=1 would call for a revision of the standard paradigm. While robust observational evidence for TeV sources at redshifts z>1 is lacking at present, the growing number of TeV blazars with redshifts as large as z~0.5 suggests the possibility that the standard blazar models may have to be reconsidered. We show that TeV gamma rays can be observed even from a source at z>1, if the observed gamma rays are secondary photons produced in inte…
Active galactic nuclei (AGN) can produce both gamma rays and cosmic rays. The observed high-energy gamma-ray signals from distant blazars may be dominated by secondary gamma rays produced along the line of sight by the interactions of cosmic-ray protons with background photons. This explains the surprisingly low attenuation observed for distant blazars, because the production of secondary gamma rays occurs, on average, much closer to Earth than the distance to the source. Thus the observed spectrum in the TeV range does not depend on the intrinsic gamma-ray spectrum, while it depends on the ou…
The Fermi-LAT telescope has unexpectedly discovered GeV gamma-ray emission from the symbiotic Nova V407 Cygni. We investigate the radiation processes due to electrons and hadrons accelerated during the explosion of this Nova. We consider a scenario in which GeV gamma-ray emission observed by Fermi is produced by the electrons with energies of a few tens of GeV in the inverse Compton scattering of stellar radiation. On the other hand, the hadrons are expected to reach larger energies, due to the lack of radiation losses during acceleration process, producing TeV gamma-rays and neutrinos. We pre…
It has been shown that the gamma-ray flux observed by HESS from the J1745-290 Galactic Center source is well fitted as the secondary gamma-rays photons generated from Dark Matter annihilating into Standard Model particles in combination with a simple power law background. The neutrino flux expected from such Dark Matter source has been also analyzed. The main results of such analyses for 50 TeV Dark Matter annihilating into W+W- gauge boson and preliminary results for antiprotons are presented.
Cosmic rays in the energy range from about 10's GeV to several 100's TeV are observed on Earth with an energy-dependent anisotropy of order 0.01-0.1%, and a consistent topology that appears to significantly change at higher energy. The nearest and most recent galactic cosmic ray sources might stochastically dominate the observation and possibly explain a change in orientation of the anisotropy as a function of energy. However, the diffusion approximation is not able to explain its non-dipolar structure and, in particular, the significant contribution of small angular scale features. Particle p…
A simple 'knee-like' approximation of the Lateral Distribution Function (LDF) of Cherenkov light emitted by EAS (extensive air showers) in the atmosphere is proposed for solving various tasks of data analysis in HiSCORE and other wide angle ground-based experiments designed to detect gamma rays and cosmic rays with the energy above tens of TeV. Simulation-based parametric analysis of individual LDF curves revealed that on the radial distance 20-500 m the 5-parameter 'knee-like' approximation fits individual LDFs as well as the mean LDF with a very good accuracy. In this paper we demonstrate th…
