Detection of extended gamma-ray emission around the Geminga pulsar with H.E.S.S

Abstract

Geminga is an enigmatic radio-quiet gamma-ray pulsar located at a mere 250 pc distance from Earth. Extended very-high-energy gamma-ray emission around the pulsar was discovered by Milagro and later confirmed by HAWC, which are both water Cherenkov detector-based experiments. However, evidence for the Geminga pulsar wind nebula in gamma rays has long evaded detection by imaging atmospheric Cherenkov telescopes (IACTs) despite targeted observations. The detection of gamma-ray emission on angular scales > 2 deg poses a considerable challenge for the background estimation in IACT data analysis. With recent developments in understanding the complementary background estimation techniques of water Cherenkov and atmospheric Cherenkov instruments, the H.E.S.S. IACT array can now confirm the detection of highly extended gamma-ray emission around the Geminga pulsar with a radius of at least 3 deg in the energy range 0.5-40 TeV. We find no indications for statistically significant asymmetries or energy-dependent morphology. A flux normalisation of $(2.8\pm 0.7)\times 10^{-12}$ cm${}^{-2}$s${}^{-1}$TeV${}^{-1}$ at 1 TeV is obtained within a 1 deg radius region around the pulsar. To investigate the particle transport within the halo of energetic leptons around the pulsar, we fitted an electron diffusion model to the data. The normalisation of the diffusion coefficient obtained of $D_0=7.6_{-1.2}^{+1.5}\times 10^{27}$ cm${}^2$s${}^{-1}$, at an electron energy of 100 TeV, is compatible with values previously reported for the pulsar halo around Geminga, which is considerably below the Galactic average.

16 pages, 15 figures, 7 tables. Accepted for publication in Astronomy & Astrophysics

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Cited by in corpus (13)

• Geminga's pulsar halo: an X-ray view
• Gamma-ray halos around pulsars: impact on pulsar wind physics and galactic cosmic ray transport
• Detection prospects of very and ultra high-energy gamma rays from extended sources with ASTRI, CTA, and LHAASO
• Effect of magnetic field correlation length on the gamma-ray pulsar halo morphology under anisotropic diffusion
• Disclosing the catalog pulsars dominating the Galactic positron flux
• Constraining the slow-diffusion zone size and electron injection spectral index for the Geminga pulsar halo
• Extended TeV Halos May Commonly Exist around Middle-Aged Pulsars
• Discrete treatment of inverse Compton scattering: implications on parameter estimation in gamma-ray astronomy
• Possible evidence for extended X-ray emission surrounding PSR B0656+14 with eROSITA
• The Potential for Hadronic Particle Acceleration in Galactic Pulsar Wind Nebulae
• Search for TeV emission from spider millisecond pulsars with HAWC
• Self-confinement of relativistic pair beams in magnetized interstellar plasmas: the case of pulsar X-ray filaments
• Anisotropic Diffusion in Pulsar Halos: Interpreting the asymmetric morphology of Geminga and Monogem halos measured by HAWC