Observation of the Galactic Center PeVatron beyond 100 TeV with HAWC
A. Albert, R. Alfaro, C. Alvarez, Amado Andrés, J. C. Arteaga-Velázquez, D. Avila Rojas, H. A. Ayala Solares, Rishi Babu, E. Belmont-Moreno, A. Bernal, K. S. Caballero‐Mora, T. Capistrán, A. Carramiñana, S. Casanova, U. Cotti, J. Cotzomi, S. Coutinõ de León, E. De la Fuente, C. de León, Davide Depaoli, N. Di Lalla, R. Diaz Hernandez, B. L. Dingus, M. A. DuVernois, J. C. Díaz–Vélez, K. Engel, T. Ergin, C. Espinoza, Kwok Lung Fan, Kwok Lung Fan, N. Fraija, S. Fraija, J. A. García-González, F. Garfias, Hazal Goksu, Magda Gonzalez, J. A. Goodman, S. Groetsch, J. P. Harding, S. Hernández-Cadena, I. Herzog, J. A. Hinton, Dezhi Huang, F. Hueyotl‐Zahuantitla, T. B. Humensky, P. Hüntemeyer, A. Iriarte, S. Kaufmann, D. Kieda, A. Lara, W. H. Lee, J. Lee, H. León Vargas, J. T. Linnemann, A. L. Longinotti, G. Luis-Raya, K. Malone, O. Martı́nez, J. Martínez-Castro, J. A. Matthews, P. Miranda-Romagnoli, Jorge Alexis Montes, J. A. Morales-Soto, E. Moreno, M. Mostafá, M. Najafi, L. Nellen, M. Newbold, M. U. Nisa, R. Noriega-Papaqui, Laura Olivera-Nieto, N. Omodei, M. Osorio-Archila, Y. Pérez Araujo, E. G. Pérez‐Pérez, Chang Dong Rho, D. Rosa‐González, E. Ruiz-Velasco, H. Salazar, D. Salazar-Gallegos, A. Sandoval, M. Schneider, Georg Schwefer, J. Serna-Franco, A. J. Smith, Y. Son, R. W. Springer, O. Tibolla, K. Tollefson, I. Torres, R. Torres-Escobedo, Rhiannon M. Turner, F. Ureña-Mena, Enrique Varela, X. Wang, Z. Wang, I. J. Watson, E. Willox, H. R. Wu, Shaoqing Yu
Abstract
Abstract We report an observation of ultrahigh-energy (UHE) gamma rays from the Galactic center (GC) region, using 7 yr of data collected by the High-Altitude Water Cherenkov (HAWC) Observatory. The HAWC data are best described as a point-like source (HAWC J1746-2856) with a power-law spectrum ( <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" overflow="scroll"> <mml:mi mathvariant="italic">d</mml:mi> <mml:mi>N</mml:mi> <mml:mrow> <mml:mo stretchy="true">/</mml:mo> </mml:mrow> <mml:mi mathvariant="italic">d</mml:mi> <mml:mi>E</mml:mi> <mml:mo>=</mml:mo> <mml:mi>ϕ</mml:mi> <mml:msup> <mml:mrow> <mml:mfenced close=")" open="("> <mml:mrow> <mml:mi>E</mml:mi> <mml:mrow> <mml:mo stretchy="true">/</mml:mo> </mml:mrow> <mml:mn>26</mml:mn> <mml:mspace width="0.25em"/> <mml:mi>TeV</mml:mi> </mml:mrow> </mml:mfenced> </mml:mrow> <mml:mrow> <mml:mi>γ</mml:mi> </mml:mrow> </mml:msup> </mml:math> ), where γ = −2.88 ± 0.15 stat − 0.1 sys and ϕ = 1.5 × 10 −15 (TeV cm 2 s) −1 <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" overflow="scroll"> <mml:mo>±</mml:mo> <mml:msub> <mml:mrow> <mml:mn>0.3</mml:mn> </mml:mrow> <mml:mrow> <mml:mi>stat</mml:mi> </mml:mrow> </mml:msub> <mml:msubsup> <mml:mrow> <mml:mspace width="0.25em"/> </mml:mrow> <mml:mrow> <mml:mo>−</mml:mo> <mml:msub> <mml:mrow> <mml:mn>0.13</mml:mn> </mml:mrow> <mml:mrow> <mml:mi>sys</mml:mi> </mml:mrow> </mml:msub> </mml:mrow> <mml:mrow> <mml:mo>+</mml:mo> <mml:msub> <mml:mrow> <mml:mn>0.08</mml:mn> </mml:mrow> <mml:mrow> <mml:mi>sys</mml:mi> </mml:mrow> </mml:msub> </mml:mrow> </mml:msubsup> </mml:math> extending from 6 to 114 TeV. We find no evidence of a spectral cutoff up to 100 TeV using HAWC data. Two known point-like gamma-ray sources are spatially coincident with the HAWC gamma-ray excess: Sgr A* (HESS J1745-290) and the Arc (HESS J1746-285). We subtract the known flux contribution of these point sources from the measured flux of HAWC J1746-2856 to exclude their contamination and show that the excess observed by HAWC remains significant (>5 σ ), with the spectrum extending to >100 TeV. Our result supports that these detected UHE gamma rays can originate via hadronic interaction of PeV cosmic-ray protons with the dense ambient gas and confirms the presence of a proton PeVatron at the GC.