Search Publications
Extinction in the Large Magellanic Cloud Bar around NGC 1854, NGC 1856, and NGC 1858
Milone, Antonino P.; Panagia, Nino; De Marchi, Guido
We report on the extinction properties in the fields around the clusters NGC 1854, NGC 1856, and NGC 1858 in the bar of the Large Magellanic Cloud. The color-magnitude diagrams of the stars in all these regions show an elongated red giant clump that reveals a variable amount of extinction across these fields, ranging from A V ≃ 0.2 to…
Local H i Emissivity Measured with Fermi-LAT and Implications for Cosmic-Ray Spectra
Casandjian, Jean-Marc
Cosmic-ray (CR) electrons and nuclei interact with the Galactic interstellar gas and produce high-energy γ-rays. The γ-ray emission rate per hydrogen atom, called emissivity, provides a unique indirect probe of the CR flux. We present the measurement and the interpretation of the emissivity in the solar neighborhood for γ-ray energy from 50 MeV to…
Analysis of the COS B Data for Evidence of Linear Polarization of VELA Pulsar Gamma Rays
Mattox, John R.; Mayer-Hasselwander, Hans A.; Strong, Andy W.
The COS B spark chamber telescope observations of the Vela pulsar were analyzed for gamma-ray polarization. No significant quadrupole moment is found in the azimuthal distribution of the electron-positron pair production planes. However, analysis of the sensitivity indicates that even 100-percent polarization would not be detected. Therefore, the …
A New Powerful Test for Periodic Pulsed Emission of High-Energy Photons
Swanepoel, J. W. H.; de Beer, C. F.
A novel stastistical test devised for detecting periodic pulsations in a series of photon arrival times is found to perform powerfully in the detection of multiple, narrow peaked light curve shapes against a uniform background, especially if the light curve has multiple peaks. The statistical test has been applied to observations of the first 1350…
CO Observations of the Cepheus Flare. II. Gamma Rays from the Interstellar Gas and a Possible New COS B Source
Grenier, I. A.; Lebrun, F.
The correlation between the distribution of the interstellar gas in the Cepheus Flare region (100^deg^ <= l <= 141^deg^, 8^deg^ <= b <= 22^deg^) and that of the diffuse gamma radiation originating in these nearby clouds has been studied in detail. A maximum-likelihood analysis has been applied to compare maps of the atomic and molecula…
Gamma-Ray Emission in MeV--GeV Region from Cygnus X-3
Li, Ti-Pei; Wu, Mei
The analysis of the simultaneous X-ray and gamma-ray observations of Cygnus X-3 by the ESA satellite COS B indicates that there exists a negative correlation between intensities of 2-12 keV X-rays and 150-5000 MeV gamma rays of Cygnus X-3. A clear image of a gamma-ray source at the position of Cygnus X-3 is obtained from the spatial distribution o…
On the High-Energy Gamma-Ray Signature of Cosmic-Ray Sources
Ormes, J. F.; Ozel, M. E.; Morris, D. J.
If cosmic rays are accelerated by strong shocks, then cosmic-ray sources should be characterized by spectra, dN/dE is proportional to p^-(2.0-2.2)^, reflecting the strength of those shocks. This is expected from the "standard leaky box" model of cosmic-ray propagation in which the source spectra are harder than the observed spectra because higher …
Search for Linear Polarization in Gamma-Ray Sources: Possible Evidence for the VELA Pulsar
Caraveo, P. A.; Bignami, G. F.; Mitrofanov, I. +1 more
The use of the azimuthal distribution of planes containing e(+)/e(-) pairs from high-energy photon materialization to investigate the nature of gamma-ray sources is discussed. Analytical work done on COS B data for bright COS B sources (Vela, Crab, and Geminga) and for a reference background region is presented along with results which are indicat…
High-Energy Gamma Rays Probing Cosmic-Ray Spectral Differences thoughout the Galaxy
Bloemen, J. B. G. M.
Detailed spectra of the Galactic γ-ray emission (50 MeV-6 GeV) are derived from a combination of all the observations obtained with the COS-B satellite. These spectra indicate that the cosmic-ray (CR) proton spectrum is on average flatter in the outer Galaxy than in the inner Galaxy and locally by approximately ∝ E0.4, and maybe more, s…
The galactic gamma-ray distribution - Implications for galactic structure and the radial cosmic-ray gradient
Harding, A. K.; Stecker, F. W.
The radial distribution of gamma ray emissivity in the Galaxy was derived from flux longitude profiles, using both the final SAS-2 results and the recently corrected COS-B results and analyzing the northern and southern galactic regions separately. The recent CO surveys of the Southern Hemisphere were used in conjunction with the Northern Hemisphe…