scholarly journals Probing the unidentified Fermi blazar-like population using optical polarization and machine learning

2019 ◽  
Vol 486 (3) ◽  
pp. 3415-3422 ◽  
Author(s):  
I Liodakis ◽  
D Blinov
Keyword(s):  
Machine Learning ◽  
Predictive Power ◽  
High Energy ◽  
Point Sources ◽  
Low Energy ◽  
Optical Polarization ◽  
Sky Surveys ◽  
Γ Ray ◽  
Energy Processes ◽  
The Universe

ABSTRACT The Fermi γ-ray space telescope has revolutionized our view of the γ-ray sky and the high-energy processes in the Universe. While the number of known γ-ray emitters has increased by orders of magnitude since the launch of Fermi, there is an ever increasing number of, now more than a thousand, detected point sources whose low-energy counterpart is to this day unknown. To address this problem, we combined optical polarization measurements from the RoboPol survey as well as other discriminants of blazars from publicly available all-sky surveys in machine learning (ML, random forest and logistic regression) frameworks that could be used to identify blazars in the Fermi unidentified fields with an accuracy of >95 per cent. Out of the potential observational biases considered, blazar variability seems to have the most significant effect reducing the predictive power of the frameworks to ${\sim }80\hbox{-}85{{\ \rm per\ cent}}$. We apply our ML framework to six unidentified Fermi fields observed using the RoboPol polarimeter. We identified the same candidate source proposed by Mandarakas et al. for 3FGL J0221.2 + 2518.

scholarly journals γ-ray astronomy balloon results

1970 ◽  
Vol 37 ◽  
pp. 315-320 ◽  
Author(s):  
C. E. Fichtel ◽  
D. A. Kniffen ◽  
H. B. Ogelman
Keyword(s):  
Cosmic Rays ◽  
Point Source ◽  
Galactic Center ◽  
High Energy ◽  
Point Sources ◽  
Positive Evidence ◽  
Γ Ray ◽  
Balloon Experiments ◽  
Energy Processes ◽  
The Universe

The significance of high energy (≳ 30 MeV) γ-Ray astronomy and its relationship to cosmic rays and many of the high energy processes of the universe has been realized for over a decade. Through the last six to eight years, searches for point sources, mostly from balloon experiments, but also Explorers 11 and OSO-3, have been unsuccessful in clearly establishing the existence of any point source. Recently on OSO-3, Clark et al. (1968) have obtained positive evidence for a celestial γ-Ray flux which is anisotropic with a higher intensity in the direction of the galactic center region. In this talk, I wish to summarize our balloon results relating to both of these questions and indicate what we hope to accomplish with our new large γ-Ray detector over the coming months.

scholarly journals Modeling Gamma-Ray SEDs and Angular Extensions of Extreme TeV Blazars from Intergalactic Proton-Initiated Cascades in Contemporary Astrophysical EGMF Models

Universe ◽  
2021 ◽  
Vol 7 (7) ◽  
pp. 220
Author(s):  
Emil Khalikov
Keyword(s):  
Gamma Rays ◽  
Large Scale ◽  
Gamma Ray ◽  
High Energy ◽  
Cascade Model ◽  
Point Sources ◽  
Spectral Energy ◽  
Observation Data ◽  
Cherenkov Telescopes ◽  
The Universe

The intrinsic spectra of some distant blazars known as “extreme TeV blazars” have shown a hint at an anomalous hardening in the TeV energy region. Several extragalactic propagation models have been proposed to explain this possible excess transparency of the Universe to gamma-rays starting from a model which assumes the existence of so-called axion-like particles (ALPs) and the new process of gamma-ALP oscillations. Alternative models suppose that some of the observable gamma-rays are produced in the intergalactic cascades. This work focuses on investigating the spectral and angular features of one of the cascade models, the Intergalactic Hadronic Cascade Model (IHCM) in the contemporary astrophysical models of Extragalactic Magnetic Field (EGMF). For IHCM, EGMF largely determines the deflection of primary cosmic rays and electrons of intergalactic cascades and, thus, is of vital importance. Contemporary Hackstein models are considered in this paper and compared to the model of Dolag. The models assumed are based on simulations of the local part of large-scale structure of the Universe and differ in the assumptions for the seed field. This work provides spectral energy distributions (SEDs) and angular extensions of two extreme TeV blazars, 1ES 0229+200 and 1ES 0414+009. It is demonstrated that observable SEDs inside a typical point spread function of imaging atmospheric Cherenkov telescopes (IACTs) for IHCM would exhibit a characteristic high-energy attenuation compared to the ones obtained in hadronic models that do not consider EGMF, which makes it possible to distinguish among these models. At the same time, the spectra for IHCM models would have longer high energy tails than some available spectra for the ALP models and the universal spectra for the Electromagnetic Cascade Model (ECM). The analysis of the IHCM observable angular extensions shows that the sources would likely be identified by most IACTs not as point sources but rather as extended ones. These spectra could later be compared with future observation data of such instruments as Cherenkov Telescope Array (CTA) and LHAASO.

scholarly journals Low Energy Indicators of High Energy Processes

2016 ◽  
Author(s):  
Franco Giovannelli ◽  
Corinne Rossi ◽  
Gennady Bisnovatyi-Kogan ◽  
Ivan Bruni ◽  
Alessandro Fasano ◽  
...  
Keyword(s):  
High Energy ◽  
Low Energy ◽  
Energy Indicators ◽  
Energy Processes

scholarly journals A NuSTAR view of powerful γ-ray loud blazars

2019 ◽  
Vol 627 ◽  
pp. A72 ◽  
Author(s):  
G. Ghisellini ◽  
M. Perri ◽  
L. Costamante ◽  
G. Tagliaferri ◽  
T. Sbarrato ◽  
...  
Keyword(s):  
Energy Distribution ◽  
Spectral Energy Distribution ◽  
Peak Frequency ◽  
High Energy ◽  
Spectral Energy ◽  
X Rays ◽  
X Ray ◽  
Γ Ray ◽  
The Universe ◽  
Jet Power

We observed three blazars at z >  2 with the NuSTAR satellite. These were detected in the γ-rays by Fermi/LAT and in the soft X-rays, but have not yet been observed above 10 keV. The flux and slope of their X-ray continuum, together with Fermi/LAT data allows us to estimate their total electromagnetic output and peak frequency. For some of them we were able to study the source in different states, and investigate the main cause of the different observed spectral energy distribution. We then collected all blazars at redshifts greater than 2 observed by NuSTAR, and confirm that these hard and luminous X-ray blazars are among the most powerful persistent sources in the Universe. We confirm the relation between the jet power and the disk luminosity, extending it at the high-energy end.

scholarly journals PMMA-Assisted Plasma Patterning of Graphene

2018 ◽  
Vol 2018 ◽  
pp. 1-8 ◽  
Author(s):  
Alfredo D. Bobadilla ◽  
Leonidas E. Ocola ◽  
Anirudha V. Sumant ◽  
Michael Kaminski ◽  
Jorge M. Seminario
Keyword(s):  
Single Molecule ◽  
Oxygen Plasma ◽  
2D Materials ◽  
High Energy ◽  
Low Energy ◽  
Graphene Ribbon ◽  
Microelectronic Fabrication ◽  
Time Required ◽  
Transistor Fabrication ◽  
Energy Processes

Microelectronic fabrication of Si typically involves high-temperature or high-energy processes. For instance, wafer fabrication, transistor fabrication, and silicidation are all above 500°C. Contrary to that tradition, we believe low-energy processes constitute a better alternative to enable the industrial application of single-molecule devices based on 2D materials. The present work addresses the postsynthesis processing of graphene at unconventional low temperature, low energy, and low pressure in the poly methyl-methacrylate- (PMMA-) assisted transfer of graphene to oxide wafer, in the electron-beam lithography with PMMA, and in the plasma patterning of graphene with a PMMA ribbon mask. During the exposure to the oxygen plasma, unprotected areas of graphene are converted to graphene oxide. The exposure time required to produce the ribbon patterns on graphene is 2 minutes. We produce graphene ribbon patterns with ∼50 nm width and integrate them into solid state and liquid gated transistor devices.

Quantum electrodynamics. II

1939 ◽  
Vol 35 (3) ◽  
pp. 438-462
Author(s):  
F. Hoyle
Keyword(s):  
Quantum Electrodynamics ◽  
Finite Size ◽  
Direct Calculation ◽  
High Energy ◽  
Low Energy ◽  
Successive Approximations ◽  
Method Of Successive Approximations ◽  
Self Energy ◽  
Energy Processes ◽  
Real Test

It is shown in this paper and the preceding one that two separate forms of theory can be developed in which a “finite size” is attributed to a charged particle by means of its interaction with the radiation field. The region attributed in this way to the particle is four dimensional and is determined in such a manner that the usual difficulties with relativistic invariance do not arise.The advantage of such a theory becomes clear when the theory is applied to those problems in which the usual calculations give infinite results. The problem of the method of successive approximations is considered and satisfactory results are obtained provided that the space dimensions of the finite region are of the order of the classical radius of the electron, when the electron is at rest.It may be noted explicitly that the difficulty that has been associated with the emission of low energy quanta by “Bremsstrahlung” will not arise in the present formulation of the electromagnetic interaction between field and particles. This case is interesting since an infinity arises here which is not analogous to the self energy infinities, but occurs in the direct calculation of a physical process and not in a virtual transition.The theory seems satisfactory so far as low energy processes (< 137 mc2) are concerned and the real test of its applicability may be expected to arise in discussing processes of high energy. It is hoped to treat these in a later paper.

scholarly journals The low energy β-rays of radium E

1934 ◽  
Vol 147 (862) ◽  
pp. 442-454 ◽  
Keyword(s):  
Energy Loss ◽  
Continuous Spectrum ◽  
Energy Region ◽  
High Energy ◽  
Experimental Information ◽  
Low Energy ◽  
Expansion Chamber ◽  
High Energy Part ◽  
Energy Part ◽  
Γ Ray

The object of this work was to obtain information about the shape of the low energy end of the continuous β-ray spectrum of radium E, an element convenient because of its negligible γ-ray emission. The failure of theory to explain the continuous spectrum makes it of interest to obtain all possible experimental information, and although much is now known about the high energy part of the curve, the low energy region has remained obscure owing to certain experimental difficulties. The chief of these has been the contamination of the low energy end of the curve by rays reflected with unknown energy loss from the material on which the radioactive body was deposited. This effect can be eliminated by mounting it on sufficiently thin metal leaf so that no particles can be reflected with appreciable loss of energy. Such a source would be too weak to use in a magnetic spectrograph, and the method therefore adopted in this work was out to mount it in a Wilson expansion chamber and take stereoscopic photographs from which the ranges of any slow tracks formed could be measured, a method already used by the writer for radium D.

Laboratory studies of electron attachment and detachment processes of aeronomic interest

1969 ◽  
Vol 47 (10) ◽  
pp. 1783-1793 ◽  
Author(s):  
A. V. Phelps
Keyword(s):  
Cross Sections ◽  
Ion Beam ◽  
Electron Attachment ◽  
Negative Ions ◽  
High Energy ◽  
Low Energy ◽  
Rate Coefficients ◽  
Dissociative Attachment ◽  
Three Body ◽  
Energy Processes

Techniques for the study of electron attachment and detachment are reviewed. The rate coefficients for the various processes of aeronomic interest are then discussed. The rates of three-body and dissociative attachment by thermal electrons have been successfully determined by swarm techniques and by high frequency studies of electrons produced by high energy particles and by photoionization. Collisional and associative detachment rates for thermal energy negative ions have been measured using the swarm and flowing afterglow techniques. Radiative attachment rates for some atmospheric negative ions have been calculated from measurements of photodetachment cross sections using crossed photon and ion beam techniques. Electron beam studies and measurements of ion kinetic energy have provided much useful information regarding the dissociative attachment process and the structure of molecular negative ions. Rate coefficients for low energy processes such as the three-body attachment to O2, the radiative attachment to O, and the associative detachment of O− in collisions with various atmospheric gases are reasonably well known. Other possibly important low energy processes, such as dissociative attachment to O3, radiative attachment to O2, and the associative detachment of O2− are less well known.

scholarly journals High Energy Pulsars: Pulses and Populations

1996 ◽  
Vol 160 ◽  
pp. 331-338 ◽  
Author(s):  
Roger W. Romani
Keyword(s):  
High Energy ◽  
Sky Surveys ◽  
X Ray ◽  
Energy Emission ◽  
Emission Models ◽  
Γ Ray ◽  
High Energy Emission

AbstractRecent X-ray and γ-ray observations have detected a number of isolated spin-powered pulsars. Studies of the pulse profiles of these objects are providing a useful guide to the site of the high energy emission. The γ-ray pulses, which are closely tied to the primary population of radiating particles, seem to be an especially useful discriminant between pulsar models. With an understanding of how the pulsar luminosity and beaming factors evolve with spin parameters, pulsar population syntheses can also be used to check the predictions of high energy emission models. In turn, comparison with γ-ray sky surveys constrains the properties of the young pulsar population.

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