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A VERITAS view of HESS J1857+026 within a multi-wavelength analysis

Y. Chen

TL;DR

VERITAS reveals extended very-high-energy emission from HESS_J1857+026 and, through a diffusion-based radial-profile analysis, derives a diffusion coefficient $D \approx (3.5 \pm 2.2) \times 10^{28}$ cm$^2$ s$^{-1}$ that is below the Galactic average, supporting a leptonic PWN scenario around PSR_J1856+0245. The morphology suggests either an additional high-energy component or broader diffusion, motivating a multi-wavelength synthesis with Fermi-LAT and HAWC data. The work highlights inhibited diffusion around pulsars as a potentially common feature and demonstrates how VHE morphology constrains particle transport and emission mechanisms in PWNe.

Abstract

HESS J1857+026 remains a mysterious gamma-ray emitter since its discovery in 2008. Despite the disclosure of a nearby pulsar and multiple studies in the high-energy (HE, E > 100 MeV) and very-high-energy (VHE, E > 100 GeV) regimes, there have been no confirmed counterparts (e.g., an SNR shell or other extended structure) in X-ray or other wavelengths. We present the result of our study of the VHE emission of HESS~J1857+026 with VERITAS as part of a multi-wavelength investigation to uncover its emission mechanisms. Our result confirms the extended nature of the source and we characterize its spectral and morphological features in the VHE band. Using the morphology of the source revealed in our analysis, we also explore the underlying transport process of a possible electron population in a leptonic PWN scenario for the gamma-ray emission.

A VERITAS view of HESS J1857+026 within a multi-wavelength analysis

TL;DR

VERITAS reveals extended very-high-energy emission from HESS_J1857+026 and, through a diffusion-based radial-profile analysis, derives a diffusion coefficient cm s that is below the Galactic average, supporting a leptonic PWN scenario around PSR_J1856+0245. The morphology suggests either an additional high-energy component or broader diffusion, motivating a multi-wavelength synthesis with Fermi-LAT and HAWC data. The work highlights inhibited diffusion around pulsars as a potentially common feature and demonstrates how VHE morphology constrains particle transport and emission mechanisms in PWNe.

Abstract

HESS J1857+026 remains a mysterious gamma-ray emitter since its discovery in 2008. Despite the disclosure of a nearby pulsar and multiple studies in the high-energy (HE, E > 100 MeV) and very-high-energy (VHE, E > 100 GeV) regimes, there have been no confirmed counterparts (e.g., an SNR shell or other extended structure) in X-ray or other wavelengths. We present the result of our study of the VHE emission of HESS~J1857+026 with VERITAS as part of a multi-wavelength investigation to uncover its emission mechanisms. Our result confirms the extended nature of the source and we characterize its spectral and morphological features in the VHE band. Using the morphology of the source revealed in our analysis, we also explore the underlying transport process of a possible electron population in a leptonic PWN scenario for the gamma-ray emission.

Paper Structure

This paper contains 8 sections, 3 equations, 3 figures, 1 table.

Table of Contents

  1. Introduction
  2. VERITAS observation and analysis
  3. The VERITAS instrument and observation
  4. VERITAS analysis
  5. VERITAS analysis results
  6. Significance map and energy spectra
  7. Diffusion coefficient
  8. Summary

Figures (3)

  • Figure 1: Significance map of region around HESS J1857+026 in 0.3 - 1 TeV (left) and in 1 - 10 TeV (right). The white contours represent significance values of 5, 6, and 7 $\sigma$. The blue dot marks the location of PSR J1856+0245.
  • Figure 2: Spectra of HESS J1857+026 and HESS J1858+020. The spectral points are extracted from the stacked dataset using the spectral index determined from the fit for each source. The lines describe the best-fit power-law spectra of the models.
  • Figure 3: Radial profile of HESS J1857+026 in the energy range of 0.3 - 10 TeV. Dashed magenta line is the fit according to Eq. \ref{['eq:radial']} and the best-fit paramter $\theta_d$ is printed in the figure.