Logo
ScienceStack
Table of Contents
Fetching ...
Sign In

A Multi-messenger Search for Ultra-high-energy Gamma Rays in Coincidence with Neutrinos

R. Alfaro, C. Alvarez, A. Andrés, E. Anita-Rangel, M. Araya, J. C. Arteaga-Velázquez, D. Avila Rojas, H. A. Ayala Solares, R. Babu, P. Bangale, E. Belmont-Moreno, A. Bernal, K. S. Caballero-Mora, T. Capistrán, A. Carramiñana, S. Casanova, U. Cotti, J. Cotzomi, S. Coutiño de León, E. De la Fuente, C. de León, P. Desiati, N. Di Lalla, R. Diaz Hernandez, M. A. DuVernois, J. C. Díaz-Vélez, K. Engel, T. Ergin, C. Espinoza, K. Fang, N. Fraija, S. Fraija, A. Galván-Gámez, J. A. García-González, F. Garfias, N. Ghosh, M. M. González, J. A. González, J. A. Goodman, S. Groetsch, D. Guevel, J. Gyeong, J. P. Harding, S. Hernández-Cadena, I. Herzog, J. Hinton, D. Huang, F. Hueyotl-Zahuantitla, P. Hüntemeyer, A. Iriarte, S. Kaufmann, A. Lara, K. Leavitt, J. Lee, T. Lewis, H. León Vargas, J. T. Linnemann, A. L. Longinotti, G. Luis-Raya, K. Malone, M. Martin, O. Martinez, J. Martínez-Castro, J. A. Matthews, P. Miranda-Romagnoli, P. E. Mirón-Enriquez, J. A. Morales-Soto, E. Moreno, M. Mostafá, M. Najafi, A. Nayerhoda, L. Nellen, N. Omodei, M. Osorio-Archila, E. Ponce, Y. Pérez Araujo, E. G. Pérez-Pérez, C. D. Rho, A. Rodriguez Parra, D. Rosa-González, M. Roth, H. Salazar, D. Salazar-Gallegos, A. Sandoval, M. Schneider, J. Serna-Franco, M. Shin, A. J. Smith, Y. Son, R. W. Springer, O. Tibolla, K. Tollefson, I. Torres, R. Torres-Escobedo, E. Varela, L. Villaseñor, X. Wang, Z. Wang, I. J. Watson, H. Wu, S. Yu, S. Yun-Cárcamo, X. Zhang, H. Zhou

Abstract

The last five years have shown us that ultra-high-energy (UHE; $>$100 TeV) gamma-ray sources are ubiquitous, but the nature of these sources remain highly uncertain. UHE gamma rays can be produced via either leptonic (Inverse compton) or hadronic (pion decay) emission mechanisms. To decisively determine the emission mechanisms, multimessenger searches are essential. Neutrinos are of particular interest as they are only created via hadronic channels. In this work, we describe a metric to select high-quality UHE events from the High Altitude Water Cherenkov (HAWC) Observatory. We use this metric to search for correlations between HAWC archival data and IceCube public neutrino alerts. 24 spatial coincidences are found, which is higher than the number of events expected by random chance. Therefore, we conclude that there are likely associations between HAWC gamma rays and IceCube neutrinos, but the angular resolutions of the two instruments prevent us from conclusively making any definitive associations between the coincidences and specific astrophysical sources. More sensitive detectors are needed.

A Multi-messenger Search for Ultra-high-energy Gamma Rays in Coincidence with Neutrinos

Abstract

The last five years have shown us that ultra-high-energy (UHE; 100 TeV) gamma-ray sources are ubiquitous, but the nature of these sources remain highly uncertain. UHE gamma rays can be produced via either leptonic (Inverse compton) or hadronic (pion decay) emission mechanisms. To decisively determine the emission mechanisms, multimessenger searches are essential. Neutrinos are of particular interest as they are only created via hadronic channels. In this work, we describe a metric to select high-quality UHE events from the High Altitude Water Cherenkov (HAWC) Observatory. We use this metric to search for correlations between HAWC archival data and IceCube public neutrino alerts. 24 spatial coincidences are found, which is higher than the number of events expected by random chance. Therefore, we conclude that there are likely associations between HAWC gamma rays and IceCube neutrinos, but the angular resolutions of the two instruments prevent us from conclusively making any definitive associations between the coincidences and specific astrophysical sources. More sensitive detectors are needed.
Paper Structure (12 sections, 3 equations, 4 figures, 4 tables)

This paper contains 12 sections, 3 equations, 4 figures, 4 tables.

Table of Contents

  1. Introduction
  2. Observatory Information
  3. The HAWC UHE alert metric
  4. Alert metric criteria
  5. Alert threshold
  6. False positive rate
  7. Systematic uncertainties
  8. Archival search with IceCube alerts
  9. Method and results
  10. False coincidence rate calculation
  11. Conclusions
  12. acknowledgments

Figures (4)

  • Figure 1: The distribution of the metric value for all UHE events passing the standard analysis cuts and a loose energy cut. The spike at zero is due to events that have either a GP or NN energy estimate above 500 TeV, where simulations are not available for comparison to data.
  • Figure 2: The metric calculated when each variable that is used in the calculation is randomly drawn according to that distribution. This is used in the false positive determination.
  • Figure 3: The average of the ten lowest chi squares in a run from September 2018, and then every 12 months afterward. The x-axis is reported in GPS Seconds, or seconds since January 1, 1980. September 2018 corresponds to approximately 1.22e9 GPS Seconds. This is used to quantify how much the left-hand (extremely gamma-like) side of the distribution is shifting in time. This effect is treated as linear in the analysis. Uncertainties are neglible.
  • Figure 4: The chi square distribution for the HAWC offline reconstruction (red) vs. the online reconstruction (black).