Combined analysis CTA plus KM3NeT

Introduction

The aim of this analysis is to simulate how well a combined analysis of CTA and KM3NeT data can differentiate between hadronic and leptonic emission scenarios of galactic gamma-ray sources. The focus is on the comparison of the combined analysis to the separate analysis of the two instruments within Gammapy. As known during leptonic emission of very high energy (VHE) gamma rays, neutrinos do not appear. Therefore, adding neutrino data to traditional gamma-ray data will increase the separation between the two possible emission scenarios. This content is only compatible with gammapy v0.17 and python 3.8, later versions are not supported.

Analysis Structure

The research considers four possible gamma sources in the Milky Way galaxy:

  • Vela X is a pulsar wind nebula bright in γ rays, associated with the well-known Vela pulsar.
  • RX J1713.7−3946 is a shell-type supernova remnant that emits γ rays in excess of 10 TeV.
  • Westerlund 1 is the most massive young stellar cluster in the galaxy.
  • eHWC J1907+063, also known as HESS J1908+063, is an unidentified γ ray source that was recently detected above energies of 100 TeV.

After that neutrino flux models were created for all sources based on experimental information about gamma observations for them. The next step requires to create the instrument response function (IRF) for both telescopes. CTA’s IRF is publicly available and requires only slight modifications for the current analysis. In turn, KM3NeT does not have a ready-made IRF, so a custom IRF was created for this, inspired by gammapy. The appropriate datasets were generated based on flux models and using IRFs for both setups CTA and KM3NeT. These datasets were used for a likelihood analysis which gave us the final significance for distinguishing between leptonic and hadronic emissions.

Summary of results for all sources and input models. The blue and red horizontal bars show the 68% and 90% quantile intervals of the distribution of best-fit values for the leptonic (fin = 0) and hadronic (fin = 1) input models, respectively. The black bars indicate the average position and sizes of the 68% credible intervals derived for each input model.

Data

  • .fits for custom KM3NeT’s IRF and for modified CTA’s IRF
  • .csv source information; flux data points of gamma observations
  • intermediate data .npy, .dat (for likelihood analysis), .fits (for datasets)

References

  • “Prospects for combined analyses of hadronic emission from γ-ray sources in the Milky Way with CTA and KM3NeT”.
    KM3NeT Collaboration and CTA Consortium, T. Unbehaun et al., (2023), e-Print: 2309.03007 astro-ph.HE
  • “Prospects for combined galactic source searches with CTA and KM3NeT”.
    Unbehaun Tim, Mohrmann Lars, Smirnov Mikhail, Schnabel Jutta & Gál Tamás. (2023), Zenodo

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