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Title: Dissecting the Cygnus region with TeV gamma rays and neutrinos

Abstract

Recent Milagro observations of the Cygnus region have revealed both diffuse TeV gamma-ray emission and a bright and extended TeV source, MGRO J2019+37, which seems to lack an obvious counterpart at other wavelengths. Additional study of this curious object also promises to provide important clues concerning one of the Milky Way's most active environments. We point out some of the principal facts involved by following three modes of attack. First, to gain insight into this mysterious source, we consider its relation to known objects in both the Cygnus region and the rest of the Galaxy. Second, we find that a simple hadronic model can easily accommodate Milagro's flux measurement (which is at a single energy), as well as other existing observations spanning nearly 7 orders of magnitude in gamma-ray energy. Third, since a hadronic gamma-ray spectrum necessitates an accompanying TeV neutrino flux, we show that IceCube observations may provide the first direct evidence of a Galactic cosmic-ray accelerator.

Authors:
 [1];  [2];  [2];  [1];  [2]
  1. Department of Physics, Ohio State University, Columbus, Ohio 43210 (United States)
  2. (United States)
Publication Date:
OSTI Identifier:
21020335
Resource Type:
Journal Article
Resource Relation:
Journal Name: Physical Review. D, Particles Fields; Journal Volume: 75; Journal Issue: 8; Other Information: DOI: 10.1103/PhysRevD.75.083001; (c) 2007 The American Physical Society; Country of input: International Atomic Energy Agency (IAEA)
Country of Publication:
United States
Language:
English
Subject:
72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS; COSMIC NEUTRINOS; COSMIC PHOTONS; COSMIC RAY DETECTION; COSMOLOGY; GAIN; GAMMA SPECTRA; HADRONS; MILKY WAY; NEUTRINOS; PHOTON EMISSION; TEV RANGE; WAVELENGTHS

Citation Formats

Beacom, John F., Department of Astronomy, Ohio State University, Columbus, Ohio 43210, Center for Cosmology and Astro-Particle Physics, Ohio State University, Columbus, Ohio 43210, Kistler, Matthew D., and Center for Cosmology and Astro-Particle Physics, Ohio State University, Columbus, Ohio 43210. Dissecting the Cygnus region with TeV gamma rays and neutrinos. United States: N. p., 2007. Web. doi:10.1103/PHYSREVD.75.083001.
Beacom, John F., Department of Astronomy, Ohio State University, Columbus, Ohio 43210, Center for Cosmology and Astro-Particle Physics, Ohio State University, Columbus, Ohio 43210, Kistler, Matthew D., & Center for Cosmology and Astro-Particle Physics, Ohio State University, Columbus, Ohio 43210. Dissecting the Cygnus region with TeV gamma rays and neutrinos. United States. doi:10.1103/PHYSREVD.75.083001.
Beacom, John F., Department of Astronomy, Ohio State University, Columbus, Ohio 43210, Center for Cosmology and Astro-Particle Physics, Ohio State University, Columbus, Ohio 43210, Kistler, Matthew D., and Center for Cosmology and Astro-Particle Physics, Ohio State University, Columbus, Ohio 43210. Sun . "Dissecting the Cygnus region with TeV gamma rays and neutrinos". United States. doi:10.1103/PHYSREVD.75.083001.
@article{osti_21020335,
title = {Dissecting the Cygnus region with TeV gamma rays and neutrinos},
author = {Beacom, John F. and Department of Astronomy, Ohio State University, Columbus, Ohio 43210 and Center for Cosmology and Astro-Particle Physics, Ohio State University, Columbus, Ohio 43210 and Kistler, Matthew D. and Center for Cosmology and Astro-Particle Physics, Ohio State University, Columbus, Ohio 43210},
abstractNote = {Recent Milagro observations of the Cygnus region have revealed both diffuse TeV gamma-ray emission and a bright and extended TeV source, MGRO J2019+37, which seems to lack an obvious counterpart at other wavelengths. Additional study of this curious object also promises to provide important clues concerning one of the Milky Way's most active environments. We point out some of the principal facts involved by following three modes of attack. First, to gain insight into this mysterious source, we consider its relation to known objects in both the Cygnus region and the rest of the Galaxy. Second, we find that a simple hadronic model can easily accommodate Milagro's flux measurement (which is at a single energy), as well as other existing observations spanning nearly 7 orders of magnitude in gamma-ray energy. Third, since a hadronic gamma-ray spectrum necessitates an accompanying TeV neutrino flux, we show that IceCube observations may provide the first direct evidence of a Galactic cosmic-ray accelerator.},
doi = {10.1103/PHYSREVD.75.083001},
journal = {Physical Review. D, Particles Fields},
number = 8,
volume = 75,
place = {United States},
year = {Sun Apr 15 00:00:00 EDT 2007},
month = {Sun Apr 15 00:00:00 EDT 2007}
}
  • TeV {gamma}-rays may provide significant information about high energy astrophysical accelerators. Such {gamma}-rays can result from the photo-de-excitation of PeV nuclei after their parents have undergone photo-disintegration in an environment of ultraviolet photons. This process is proposed as a candidate explanation of the recently discovered HEGRA source at the edge of the Cygnus OB2 association. The Lyman-{alpha} background is provided by the rich O and B stellar environment. It is found that (1) the HEGRA flux can be obtained if there is efficient acceleration at the source of lower energy nuclei; (2) the requirement that the Lorentz-boosted ultraviolet photons canmore » excite the giant dipole resonance implies a strong suppression of the {gamma}-ray spectrum compared to an E{sub {gamma}}{sup -2} behavior at energies < or approx. 1 TeV (some of these energies will be probed by the upcoming GLAST mission); (3) a TeV neutrino counterpart from neutron decay following helium photo-disintegration will be observed at IceCube only if a major proportion of the kinetic energy budget of the Cygnus OB2 association is expended in accelerating nuclei.« less
  • The diffuse gamma radiation arising from the interaction of cosmic ray particles with matter and radiation in the Galaxy is one of the few probes available to study the origin of the cosmic rays. Milagro is a water Cherenkov detector that continuously views the entire overhead sky. The large field-of-view combined with the long observation time makes Milagro the most sensitive instrument available for the study of large, low surface brightness sources such as the diffuse gamma radiation arising from interactions of cosmic radiation with interstellar matter. Recent development in the analysis techniques used by the Milagro collaboration had resultedmore » in the discovery of an extended TeV gamma-ray source in the Cygnus region of the Galaxy. The new source MGRO J2019+37 has been detected at median energies of 12 TeV In addition, diffuse emission of TeV gamma-rays from Cygnus region was observed.« less
  • We report the observation of TeV {gamma}-rays from the Cygnus region using the ARGO-YBJ data collected from 2007 November to 2011 August. Several TeV sources are located in this region including the two bright extended MGRO J2019+37 and MGRO J2031+41. According to the Milagro data set, at 20 TeV MGRO J2019+37 is the most significant source apart from the Crab Nebula. No signal from MGRO J2019+37 is detected by the ARGO-YBJ experiment, and the derived flux upper limits at the 90% confidence level for all the events above 600 GeV with medium energy of 3 TeV are lower than themore » Milagro flux, implying that the source might be variable and hard to be identified as a pulsar wind nebula. The only statistically significant (6.4 standard deviations) {gamma}-ray signal is found from MGRO J2031+41, with a flux consistent with the measurement by Milagro.« less
  • The diffuse gamma radiation arising from the interaction of cosmic ray particles with matter and radiation in the Galaxy is one of the few probes available to study the origin of the cosmic rays. Milagro is a water Cherenkov detector that continuously views the entire overhead sky. The large field-of-view combined with the long observation time makes Milagro the most sensitive instrument available for the study of large, low surface brightness sources such as the diffuse gamma radiation arising from interactions of cosmic radiation with interstellar matter. In this paper we present spatial and flux measurements of TeV gamma-ray emissionmore » from the Cygnus Region. The TeV image shows at least one new source MGRO J2019+37 as well as correlations with the matter density in the region as would be expected from cosmic-ray proton interactions. However, the TeV gamma-ray flux as measured at {approx}12 TeV from the Cygnus region (after excluding MGRO J2019+37) exceeds that predicted from a conventional model of cosmic ray production and propagation. This observation indicates the existence of either hard-spectrum cosmic-ray sources and/or other sources of TeV gamma rays in the region.« less
  • Milagro is a TeV gamma-ray observatory that utilizes a large water Cherenkov detector to observe extensive air showers (EAS) produced by high energy particles impacting the Earth's atmosphere. Milagro's distinct advantage compared to other TeV gamma-ray detectors is that it views a wide field (2 steradian overhead sky) and it continuously operates (> 90% live time ). These factors give Milagro the potential for discovery of new sources with unknown positions and times, such as gamma-ray bursts, flaring AGNs, and observation of diffuse and extended sources like the Galactic plane or large supernova remnants. Here we present a new techniquemore » for improving background rejection in Milagro as well as a gamma-ray image of the Cygnus region at energies near 12.5 TeV. We report the detection of both an extended source and a large area of diffuse gamma-ray emission from this region of the galaxy. This new extended source has an extent of 0.32 {+-} 0.12 degrees and an integral flux above 12.5 TeV of (1.71 {+-} 0.24stat {+-} 0.34sys) x 10-13cm-2s-1 assuming a differential source spectrum of E-2.6. The best-fit location for the source is RA = 304.66 {+-} 0.13stat {+-} 0.25sys degrees and declination 36.96 {+-} 0.08stat {+-} 0.2sys degrees.« less