Search for point sources of high-energy cosmic gamma rays

A balloon-borne photographic spark chamber was flown at a pressure of 10 g cm−2 on 14 April 1966 from Holloman A.F.B., New Mexico. Upper limits were obtained on gamma-ray fluxes above 1 GeV from various discrete sources including Cyg A, Cas A, and the Crab nebula. Also a measurement was made on the average photon flux above 1 GeV from a portion of the galactic disk.

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Gamma-ray flaring activity of NGC1275 in 2016–2017 measured by MAGIC

Astronomy and Astrophysics ◽

10.1051/0004-6361/201832895 ◽

2018 ◽

Vol 617 ◽

pp. A91 ◽

Cited By ~ 9

Author(s):

◽

S. Ansoldi ◽

L. A. Antonelli ◽

C. Arcaro ◽

D. Baack ◽

...

Keyword(s):

Gamma Rays ◽

Gamma Ray ◽

Crab Nebula ◽

High Energy ◽

Plausible Model ◽

Very High Energy ◽

Gamma Ray Emission ◽

Radio Band ◽

Optical Flux ◽

The Crab Nebula

We report on the detection of flaring activity from the Fanaroff-Riley I radio galaxy NGC 1275 in very-high-energy (VHE, E > 100 GeV) gamma rays with the Major Atmospheric Gamma Imaging Cherenkov (MAGIC) telescopes. The observations were performed between 2016 September and 2017 February, as part of a monitoring programme. The brightest outburst, with ∼1.5 times the Crab Nebula flux above 100 GeV (C.U.), was observed during the night between 2016 December 31 and 2017 January 1. The flux is fifty times higher than the mean flux previously measured in two observational campaigns between 2009 October and 2010 February and between 2010 August and 2011 February. Significant variability of the day-by-day light curve was measured. The shortest flux-doubling timescale was found to be of (611 ± 101) min. The spectra calculated for this period are harder and show a significant curvature with respect to the ones obtained in the previous campaigns. The combined spectrum of the MAGIC data during the strongest flare state and simultaneous data from the Fermi-LAT around 2017 January 1 follows a power law with an exponential cutoff at the energy (492 ± 35) GeV. We further present simultaneous optical flux density measurements in the R-band obtained with the Kungliga Vetenskaps Akademien (KVA) telescope and investigate the correlation between the optical and gamma-ray emission. Due to possible internal pair-production, the fast flux variability constrains the Doppler factor to values that are inconsistent with a large viewing angle as observed in the radio band. We investigate different scenarios for the explanation of fast gamma-ray variability, namely emission from magnetospheric gaps, relativistic blobs propagating in the jet (mini-jets), or an external cloud (or star) entering the jet. We find that the only plausible model to account for the luminosities here observed would be the production of gamma rays in a magnetospheric gap around the central black hole, only in the eventuality of an enhancement of the magnetic field threading the hole from its equipartition value with the gas pressure in the accretion flow. The observed gamma-ray flare therefore challenges all the discussed models for fast variability of VHE gamma-ray emission in active galactic nuclei.

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

Universe ◽

10.3390/universe7070220 ◽

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.

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Time-Domain Astronomy with Swift, Fermi and Lobster

Proceedings of the International Astronomical Union ◽

10.1017/s174392131200018x ◽

2011 ◽

Vol 7 (S285) ◽

pp. 41-46 ◽

Cited By ~ 2

Author(s):

Neil Gehrels ◽

Scott D. Barthelmy ◽

John K. Cannizzo

Keyword(s):

Gamma Ray ◽

Crab Nebula ◽

High Energy ◽

Tidal Disruption ◽

X Ray ◽

Order Of Magnitude ◽

New Type ◽

The Crab Nebula ◽

High Energy Emission ◽

Higher Sensitivity

AbstractThe dynamic transient gamma-ray sky is revealing many interesting results, largely due to findings by Fermi and Swift. The list includes new twists on gamma-ray bursts (GRBs), a GeV flare from a symbiotic star, GeV flares from the Crab Nebula, high-energy emission from novae and supernovae, and, within the last year, a new type of object discovered by Swift—a jetted tidal disruption event. In this review we present highlights of these exciting discoveries. A new mission concept called Lobster is also described; it would monitor the X-ray sky at order-of-magnitude higher sensitivity than current missions can.

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The expected high-energy to ultra-high-energy gamma-ray spectrum of the Crab Nebula

The Astrophysical Journal ◽

10.1086/171706 ◽

1992 ◽

Vol 396 ◽

pp. 161 ◽

Cited By ~ 179

Author(s):

O. C. de Jager ◽

A. K. Harding

Keyword(s):

Gamma Ray ◽

Crab Nebula ◽

High Energy ◽

Ultra High Energy ◽

High Energy Gamma ◽

Energy Gamma ◽

The Crab Nebula

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Detection of High-Energy Gamma Rays from the Crab Nebula

The Astrophysical Journal ◽

10.1086/180998 ◽

1972 ◽

Vol 175 ◽

pp. L117 ◽

Cited By ~ 59

Author(s):

G. G. Fazio ◽

H. F. Helmken ◽

E. O'Mongain ◽

T. C. Weekes

Keyword(s):

Gamma Rays ◽

Crab Nebula ◽

High Energy ◽

High Energy Gamma ◽

Energy Gamma ◽

The Crab Nebula

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Recent Results on the Search for 1011 eV Gamma Rays from the Crab Nebula

Symposium - International Astronomical Union ◽

10.1017/s007418090000721x ◽

1971 ◽

Vol 46 ◽

pp. 65-67

Author(s):

G. G. Fazio ◽

H. F. Helmken ◽

G. H. Rieke ◽

T. C. Weekes

Keyword(s):

Magnetic Field ◽

Gamma Rays ◽

Gamma Ray ◽

Crab Nebula ◽

Cosmic Ray ◽

Air Showers ◽

Upper Limit ◽

The Crab Nebula ◽

Cerenkov Light ◽

Significant Flux

The detection of Čerenkov light emitted by cosmic-ray air showers was used to search for cosmic gamma rays from the Crab Nebula. By use of the 10-m optical reflector at Mt. Hopkins, Arizona, the Crab Nebula was observed during the winter of 1969–1970 for approximately 112 hours, which was a significant increase in exposure time over previous experiments. Above a gamma-ray energy of 2.2 × 1011 eV, no significant flux was detected, resulting in an upper limit to the flux of 8.1 × 10-11 photon/cm2 sec. In the synchrotron-Compton-scattering model of gamma-ray production in the Crab Nebula, this limit on the flux indicates the average magnetic field in the nebula must be greater than 3 × 10-4 G.

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Sky survey of high-energy cosmic X-rays and spectral information on sources in the Crab nebula, Cygnus, and Scorpius

Canadian Journal of Physics ◽

10.1139/p68-259 ◽

1968 ◽

Vol 46 (10) ◽

pp. S409-S413 ◽

Cited By ~ 12

Author(s):

Walter H. G. Lewin ◽

George W. Clark ◽

William B. Smith

Keyword(s):

Crab Nebula ◽

High Energy ◽

X Rays ◽

Coma Cluster ◽

X Ray ◽

Sky Survey ◽

Upper Limits ◽

Intensity Ratios ◽

The Crab Nebula ◽

Made In

A complete X-ray survey of the northern sky has been made in the energy range 20–100 keV. Spectra are given for Cyg X-1 and Tau X-1. Intensity ratios (Cyg X-1/Tau X-1) of 0.84 ± 0.10 and 1.30 ± 0.25 were derived in the 20–70 keV range from data obtained on July 19, 1966 and February 13, 1967, respectively. Observations on Sco X-1 and the Coma cluster show upper limits which are quite different from results reported by other groups.

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