High-energy tail of the Galactic Center gamma-ray excess

Journal Article · Wed Nov 30 00:00:00 EST 2016 · Physical Review. D.

DOI:https://doi.org/10.1103/physrevd.94.103013· OSTI ID:1505801

Linden, Tim ^[1]; Rodd, Nicholas L. ^[2]; Safdi, Benjamin R. ^[2]; Slatyer, Tracy R.  ^[2]

---

1. Univ. of Chicago, IL (United States). Kavli Inst. for Cosmological Physics; The Ohio State Univ., Columbus, OH (United States). Center for Cosmology and AstroParticle Physics (CCAPP). Dept. of Physics
2. Massachusetts Inst. of Technology (MIT), Cambridge, MA (United States). Center for Theoretical Physics

Observations by the Fermi-LAT have uncovered a bright, spherically symmetric excess surrounding the center of the Milky Way Galaxy. The spectrum of the $${\gamma}$$-ray excess peaks sharply at an energy $${\sim}2\text{ }\text{ }\mathrm{GeV}$$, exhibiting a hard spectrum at lower energies, and falls off quickly above an energy $${\sim}5\text{ }\text{ }\mathrm{GeV}$$. The spectrum of the excess above $${\sim}10\text{ }\text{ }\mathrm{GeV}$$ is potentially an important discriminator between different physical models for its origin. We focus on observations of the $${\gamma}$$-ray excess at energies exceeding 10 GeV, finding: (1) a statistically significant excess remains in the energy range 9.5–47.5 GeV, which is not degenerate with known diffuse emission templates such as the Fermi bubbles, (2) the radial profile of the excess at high energies remains relatively consistent with data near the spectral peak (3) the data above $${\sim}5\text{ }\text{ }\mathrm{GeV}$$ prefer a slightly greater ellipticity with a major axis oriented perpendicular to the Galactic plane. Using the recently developed non-Poissonian template fit, we find mild evidence for a point-source origin for the high-energy excess, although given the statistical and systematic uncertainties we show that a smooth origin of the high-energy emission cannot be ruled out. We discuss the implication of these findings for pulsar and dark matter models of the $${\gamma}$$-ray excess. Finally we provide a number of updated measurements of the $${\gamma}$$-ray excess, utilizing novel diffuse templates and the Pass 8 data set.

• Research Organization: Massachusetts Inst. of Technology (MIT), Cambridge, MA (United States); Univ. of Chicago, IL (United States)
• Sponsoring Organization: USDOE Office of Science (SC), High Energy Physics (HEP); National Aeronautics and Space Administration (NASA)
• Grant/Contract Number: SC0013999; SC0012567; PF3-140110
• OSTI ID: 1505801
• Alternate ID(s): OSTI ID: 1333987
• Report Number(s): MIT-CTP/4796
• Journal Information: Physical Review. D., Vol. 94, Issue 10; ISSN 2470-0010
• Publisher: American Physical Society (APS)
• Country of Publication: United States
• Language: English

Related Subjects

79 ASTRONOMY AND ASTROPHYSICS
72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS
dark matter
gamma ray astronomy