Discovery of a Spatially Extended GeV Source in the Vicinity of the TeV Halo Candidate 2HWC J1912+099: a TeV Halo or Supernova Remnant?

Hai-Ming Zhang,Ruo-Yu Liu,Siming Liu,Xiang-Yu Wang,Shao-Qiang Xi,Yu-Liang Xin

doi:10.3847/1538-4357/ab5af6

Abstract

Abstract Observations by the High-Altitude Water Cherenkov Observatory (HAWC) and Milagro have detected spatially extended TeV sources surrounding middle-aged (t ∼ 100–400 kyr) pulsars like Geminga and PSR B0656+14, which have been named “TeV halos,” representing very extended TeV pulsar wind nebulae (PWNe) powered by relatively old pulsars. A few more HAWC-detected sources have been suggested to be TeV halo candidates. In this paper, we search for possible GeV counterparts of three TeV halo candidates with Fermi Large Area Telescopes. We detect a new spatially extended GeV source in the vicinity of the TeV halo candidate 2HWC J1912+099, which is also detected by the High Energy Stereoscopic System (H.E.S.S.) (HESS J1912+101). We find that the size of the GeV source is significantly larger than that of the TeV emission measured by H.E.S.S., and a spatial template characteristic of a PWN can fit the GeV data. We suggest that the GeV source is an extended PWN powered by the central middle-aged pulsar PSR J1913+1011. This discovery favors the TeV halo scenario for the TeV source 2HWC J1912+099 (HESS J1912+101), although the possible shell-like morphology measured by H.E.S.S. challenges this interpretation. Alternatively, the TeV emission could be dominated by a supernova remnant via the hadronic process. Future multi-wavelength observations of the source and more precise measurements of the spatial profile of the TeV emission will be useful to distinguish between the two scenarios.

Highlights

Observations from Milagro (Abdo et al 2009), along with recent observations by High-Altitude Water Cherenkov Observatory (HAWC) (Abeysekara et al 2017a), have revealed extended TeV emissions (i.e., TeV halos) surrounding Geminga and PSR B0656+14
Using ∼10.4 yr of Fermi-Large Area Telescope (LAT) data, we discovered a new extended GeV source in the vicinity of the TeV source 2HWC J1912+099, which is detected by H.E.S.S. (HESS J1912+101)
The best-fit extension of the GeV γ-ray emission is 0°.85 ± 0°.08 using the uniform-disk template, significantly larger than the size of the TeV emission measured by H.E.S.S. (∼0°.5)

Summary

Introduction

Observations from Milagro (Abdo et al 2009), along with recent observations by HAWC (Abeysekara et al 2017a), have revealed extended TeV emissions (i.e., TeV halos) surrounding Geminga and PSR B0656+14. Xi et al (2019) argued that GeV observations provide more direct constraints on the positron density in the TeV nebulae in the energy range of 10–500 GeV and on the origin of the observed positron excess Motivated by this, they searched for GeV emission from the two TeV halos with the Fermi Large Area Telescope (LAT). Considering the proper motion of the Geminga pulsar and one-zone diffusion spatial templates, which leads to a very large size for the source, Di Mauro et al (2019) claimed the detection of GeV emission from the Geminga TeV halo. The two red dashed circles indicate the outer and inner radii of the shell model for the TeV source HESS J1912+101 (H.E.S.S. Collaboration et al 2018), while the yellow and the white dashed circles indicate the extents of 2HWC J1912+099 (Abeysekara et al 2017a) and the GeV emission (uniform-disk template) in this work, respectively.

Single Point-like Source Model

Uniform Disk Template

Diffusion Templates in the TeV Halo Scenario

Findings

Conclusions