Conveners
Gamma rays
- Michelle Hui
Gamma rays
- Gareth Hughes (Smithsonian Center for Astrophysics)
Gamma rays
- Maria Petropoulou (Purdue University)
Gamma rays
- Yoshiyuki Inoue (ISAS/JAXA)
Gamma rays
- Yoshiyuki Inoue (ISAS/JAXA)
Gamma rays
- Hugo Ayala (Pennsylvania State University)
For more than a decade VERITAS, an imaging atmospheric-Cherenkov telescope array, has been probing the Northern very-high-energy (VHE; >100 GeV) gamma-ray sky. Located in Southern Arizona, VERITAS consists of four 12-m diameter reflectors and is one of the worlds most sensitive detectors of gamma rays between 85-GeV to 30-TeV. Over 50 galactic and extra-galactic sources have been detected at...
For more than a decade the MAGIC Collaboration is delivering outstanding results in the field of very high energy gamma-ray physics.
The two 17m telescope system is one of the best performing instruments in its class, especially at low energies,
crucial for observations of e.g. high redshift sources, pulsars and GRBs. This talk will discuss recent key results from Galactic and extragalactic...
It is widely believed that Galactic Cosmic Rays (CR) are accelerated in Supernova Remnants (SNRs) through the process of diffusive shock acceleration. In this scenario, particles should be accelerated up to energies around 1 PeV (the so-called 'Knee') and emit gamma rays. To test this hypothesis, precise measurements of the gamma-ray spectra of young SNRs at TeV energies are needed. Among the...
TeV observations of gamma-ray sources are very important probes of cosmic-ray accelerators, as leptonic and hadronic spectra differ in this energy range. The High Altitude Water Cherenkov (HAWC) Observatory, located in Puebla, Mexico, is capable of detecting air showers initiated by gamma rays in the multi-TeV energy range. The upper end of this range is previously unexplored. The detector...
We present results of a search for galactic PeV gamma rays with the IceCube observatory, presently the most sensitive facility for PeV gamma-ray sources in the Southern Hemisphere. This includes a search for point sources over IceCube’s field of view, as well as tests for correlations with TeV sources detected by H.E.S.S. and neutrino events from IceCube’s high energy starting event sample,...
Recent HAWC observations have found extended TeV emission coincident with the Geminga and Monogem pulsars. In this talk, I will show that these detections have significant implications for our understanding of pulsar emission. The isotropic nature of this emission provides a new avenue for detecting nearby pulsars with radio beams that are not oriented towards Earth. Additionally, I will show...
Several starburst galaxies have been observed in the GeV and TeV bands; in this
regime, gamma-rays are mainly produced by cosmic-ray interactions with the interstellar medium ($p_{\rm cr}p_{\rm ism} \to \pi^{0} \to \gamma\gamma$). Furthermore, the dense environments of starbursts may act as proton "calorimeters" where collisions dominate losses, so that a substantial fraction of cosmic-ray...
When analyzed together, radio and gamma-ray observations make for a very powerful tool for studying and diagnosing extragalactic cosmic ray populations. The recent gamma-ray detection of the ultra-luminous galaxy Arp 220 is well above past predictions, indicating evidence of a very large cosmic ray population. Whether the star formation or an active galactic nucleus is the source of the...
It has been suggested that high-energy gamma-ray emission ($>$100MeV ) of nearby star-forming galaxies may be produced predominantly by cosmic rays colliding with the interstellar medium through neutral pion decay. The pion-decay mechanism predicts a unique spectral signature in the gamma-ray spectrum, characterized by a fast rising spectrum and a spectral break below a few hundreds of MeV. We...
The repeating fast radio burst (FRB) 121102 was recently localized to a star-forming region in a dwarf host galaxy remarkably similar to those of superluminous supernovae (SLSNe) and long gamma-ray bursts (GRB), both of which were previously proposed to be powered by the birth of a millisecond magnetar. We demonstrate how a single magnetar engine can power both a SLSN and GRB, depending on the...
Optical Synchrotron emission from blazars is significantly polarized and the polarization probes the magnetic field structure in the jet. Rotations of the polarization angle in blazars reveal important information about the evolution of disturbances responsible for blazar flares. Early results indicated that such rotations might be coincident with unusual gamma-ray activity of such sources....
Blazars are thought to possess a relativistic jet that is pointing toward the direction of the Earth and the effect of relativistic beaming enhances its apparent brightness. Although numerous measurements have been performed, the mechanisms behind jet variability, creation, and composition are still debated.
We performed simultaneous gamma-ray and optical photopolarimetry observations
of 45...
By using deep radio source catalogs currently available, we present a new blazar candidate catalog, BROS, which includes 56314 sources located at declination $\delta > -40^{\circ}$ and outside the Galactic Plane ($|b| > 10^{\circ}$). We picked up flat-spectrum radio sources of $\alpha > -0.5$ ($\alpha$ is defined as $F_{\nu} \propto \nu^{\alpha}$) from 0.15 GHz TGSS and 1.4 GHz NVSS catalogs....
Recent high-energy missions have allowed keeping watch over quasars in flaring states, which provide deep insights into the engine powered by supermassive black holes. However, having a quasar caught in a very bright flaring state is not easy requiring long surveys. Therefore, the observation of such flaring events represents a goldmine for theoretical studies.
Such a flaring event was...
With the installation of a fifth 28-m diameter telescope in the center of the array, the H.E.S.S. telescope array is now in its phase II, characterized by a low energy threshold below 100 GeV. The low-energy window is particularly appealing for extragalactic gamma-ray astronomy, because it allows the study of more distant sources, as well as sources characterized by softer spectra. In...
Radio Galaxies are the most likely class of sources for the diffuse flux of high-energy neutrinos reported by the IceCube Collaboration as suggested by multi-messenger data. Here, the gamma-ray spectrum from four nearby radio galaxies (Centaurus A, PKS 0625-35, NGC 1275, and IC 310) is analyzed in order to constrain the spectral shape and intensity of their respective injected emission. Our...
The Compton Spectrometer and Imager is a 0.2-5 MeV Compton telescope capable of imaging, spectroscopy and polarimetry of astrophysical sources. Such capabilities are made possible by COSI's twelve germanium cross-strip detectors, which provide for high efficiency, high resolution spectroscopy, and precise 3D positioning of photon interactions. In May 2016, COSI took flight from Wanaka, New...
The blazar Mrk 501 is a well-known BL-Lac type object emitting very high energy photons interacting with the EBL despite the modest redshift and is highly variable across wavelengths down to timescales of a few minutes at TeV energies. This makes it an excellent laboratory for
studying particle acceleration and radiative emission processes in jets
through the spectral and temporal properties...
Recent results on the Extragalactic Background Light (EBL) intensity obtained from a combined likelihood analysis of blazar spectra detected by the MAGIC telescopes are reported. The EBL is the optical-infrared diffuse background light accumulated during galaxy evolution, directly and/or reprocessed by dust, which provides unique information about the history of galaxy formation. The low...
We have calculated the extragalactic IR-UV photon density as a function of redshift, and the resulting IR-UV spectrum of the extragalactic background light. Our empirically-based approach is based on local-to-deep galaxy survey data obtained in different wavelength bands using many space-based telescopes. This approach allowed us, for the first time, to obtain a completely model independent...
Gamma-rays with energy exceeding 100 GeV emitted by extragalactic sources initiate cascades in the intergalactic medium. The angular and temporal distribution of the cascade photons that arrive at the Earth depend on the strength and configuration of extragalactic magnetic fields in the line of sight. For weak enough fields, extended emission around the source (halo) is expected to be...
We report on the Fermi High-Latitude Extended Source Catalog (FHES), a systematic search for spatial extension of gamma-ray point sources detected with the Fermi Large Area Telescope (LAT) at Galactic latitudes |b| > 5 degrees. Point sources listed in the 3FGL and 3FHL catalogs are used for this search. While the majority of high-latitude LAT sources are extragalactic blazars that appear...
The very high energy ($E > 100 $ GeV) gamma-ray flux from extragalactic sources is attenuated due to $e^+e^-$ pair production on the extragalactic background light (EBL). This attenuation process can lead to the development of electromagnetic cascades from the inverse-Compton scattering of background photons by the produced $e^+e^-$ pairs. The cascade secondary gamma-ray emission is...
Poisson regression of the Fermi-LAT data in the inner Milky Way reveals an extended gamma-ray excess. An important question is whether the signal is coming from a collection of unresolved point sources, possibly old recycled pulsars, or constitutes a truly diffuse emission component. Previous analyses have relied on non-Poissonian template fits or wavelet decomposition of the Fermi-LAT data,...
All models for Galactic diffuse gamma-ray emission share one property: They
give formally a remarkably bad fit to the data. A large number of statistically significant residuals remain, making it very challenging to discriminate genuine features in the data from analysis artefacts.
We present SkyFACT (Sky Factorization with Adaptive Constrained Templates) [1], a new approach for studying,...
The High-Altitude Water-Cherenkov (HAWC) experiment is a TeV gamma-ray
observatory located at 4100 m above sea level on the Sierra Negra mountain in
Puebla, Mexico. Each of the detector's 300 water-filled tanks is instrumented
with four photomultiplier tubes that detect the Cherenkov radiation produced by
charged particles created in extensive air showers. With an instantaneous
field of view...
We present a self-consistent model of the Fermi Bubbles, described as a decelerating outflow of gas and non-thermal particles produced within the Galactic center region, on a $\sim 100$ Myr timescale. Motivated by observations, we use an outflow with velocity O(100 km/s), which is slower than the velocities used in models describing the Bubbles as a more recent outburst. We take into account...
Cosmic rays can be probed by their non thermal emission in the radio and in gamma-ray bands. One-zone models of cosmic rays have been used to match the integrated emission of starburst galaxies. We construct multi-dimensional models of the local starburst M82 using cosmic ray propagation code GALPROP. Using the integrated gamma-ray and radio spectra, along with the vertical distribution of...
The Cherenkov Telescope Array (CTA) will be a new observatory to study
very-high-energy gamma-ray sources. It is designed to achieve an order of
magnitude improvement in sensitivity in the 20 GeV to 300 TeV energy band
compared to currently operating instruments: VERITAS, MAGIC, and H.E.S.S. CTA
will probe known sources with unprecedented sensitivity, angular resolution, and
spectral coverage,...
The ALPACA (Andes Large area PArticle detector for Cosmic ray physics and Astronomy) experiment is aimed at observing cosmic gamma rays above 10 TeV in the southern sky with wide field of view and high sensitivity.
We will construct an 83,000 m^2 surface air-shower array and a 5,400 m^2 underground muon detector array,
on a highland (Chacaltaya Hill) at the altitude of 4,740 m halfway up Mt....
The MeV domain is one of the most underexplored windows on the Universe. From astrophysical jets and extreme physics of compact objects to a large population of unidentified objects, fundamental astrophysics questions can be addressed by a mission that opens a window into the MeV range. AMEGO is a wide-field gamma-ray telescope with sensitivity from ~200 keV to >10 GeV. AMEGO provides three...
The Lunar Occultation Explorer (LOX) is a paradigm shift - a next-generation mission concept that will provide new capabilities in time-domain nuclear astrophysics and establish the Moon as a platform for nuclear astrophysics. Currently under review by NASA’s Explorer Program, LOX's performance requirements are driven by focused science goals designed to resolve the enigma of Type-Ia supernova...
We present some of the main results from the Third Catalog of Hard Fermi-LAT Sources (3FHL). This catalog, based on the first 7 years of LAT data using the Pass 8 event-level analysis, contains 1556 sources characterized in the 10 GeV--2 TeV energy range. The sensitivity and angular resolution are improved by factors of 3 and 2 relative to the previous LAT catalog in this energy range (1FHL)....
