Can a single supernova remnant account for the gamma-ray emission of G106.3+2.7?

Abstract

SNR G106.3+2.7 is a complex TeV emitting source whose emission is still poorly understood. It has especially been at the center of numerous discussions on its potential for being a supernova remnant (SNR) PeVatron, since its gamma-ray spectra seems not to exhibit any significant suppression in the multi--TeV range, up to $\sim 600$ TeV, thereby indicating the presence of $\sim$ PeV particles. We study the hypothesis in which a SNR evolving in a clumpy or cloudy environment is powering the TeV gamma-ray emission, detected mainly from two regions, the "head" and the "tail". We discuss the implications of such an hypothesis. We rely on a simple physically motivated analytical modeling of the shock dynamics and of the content of accelerated particles and confront it to available gamma-ray observations. We find that the current observed TeV gamma-ray emission in the head and tail regions can be accounted for by an active single SNR, with a natural hardening of the spectrum due to the expansion in a clumpy medium or escaping to a dense region in the tail. However, in all scenarios, the broadband gamma-ray emission from the GeV range to the $\gtrsim 100$ TeV range is difficult to reconcile with a standard SNR - whether originating from a thermonuclear or a core-collapse supernova - and instead points toward an association with the pulsar.

Figures (5)

• Figure 1: G106.3+2.7 as observed by MAGIC abe2023. The color scale shows the significance map of photons with energies above 0.2 TeV. The white contours correspond to radio observations at 1420 MHz from the Dominion Radio Astrophysical Observatory (DRAO) Synthesis Telescope pineault2000. The small solid blue circle indicates the position of J2229+6114. The green circles represent the LHAASO observations 2022AA...658A..60Y, with the thick circle corresponding to the WCDA data and the thin one to KM2A; the centre of the detected emission is marked with an ‘x’. The dashed black circle (diameter 0.3$^{\circ}$) and ellipse (major axis 0.9$^{\circ}$) indicate the minimal and maximal SNR shock sizes considered in this work.
• Figure 2: Angular diameter of the SNR shock (2$\times r_{\rm sh}$ as a function of its distance and age. The SNR shock expands in a structured CSM, first through the dense RSG wind and then through a low--density bubble ($n_{\rm b}=10^{-2}\,\mathrm{cm}^{-3}$), in which it evolves for most of its lifetime.
• Figure 3: Time evolution of the maximum momentum of accelerated particles when the amplified magnetic field is driven by the growth of non--resonant streaming instabilities bell2013. Type Ia (solid yellow), Type II (dot-dashed blue), Type II with an extended low density bubble of size $r_{\rm b}=100$ pc (dashed red), and Type II* (dotted green) SN progenitors are considered. The best-fit found in Sec. \ref{['sec:broad']} is shown in dashed black.
• Figure 4: Gamma-ray emission from a SNR shock from a Type II SNe, expanding in a uniform medium (dashed red), propagating into a clumpy medium (solid blue), and from protons that have escaped the shock and interact with a cloud of density $10^2$ cm$^{-3}$, radius 5 pc, located at 10 pc from the SNR shock wave (dotted blue). The first scenario readily accounts for the MAGIC observations of the head (red data points), whereas the second and third scenarios can explain the MAGIC observations of the tail (blue data points).
• Figure 5: Best-fitting hadronic models obtained from our grid search. Flux points from each instrument were used to select the models. Observationnal data points are taken from Fermi-LAT 2019ApJ...885..162X, VERITAS 2009ApJ...703L...6A, and LHAASO 2022AA...658A..60Y. The color of the models' curves go from dark to light-red going from the best to worse model likelihood.