Deep Morphological and Spectral Study of the SNR RCW 86 With Fermi-Lat

Abstract

RCW 86 is a young supernova remnant (SNR) showing a shell-type structure at several wavelengths and is thought to be an efficient cosmic-ray (CR) accelerator. Earlier Fermi Large Area Telescope results reported the detection of γ-ray emission coincident with the position of RCW 86 but its origin (leptonic or hadronic) remained unclear due to the poor statistics. Thanks to 6.5 years of data acquired by the Fermi-LAT and the new event reconstruction Pass 8, we report the significant detection of spatially extended emission coming from RCW 86. The spectrum is described by a power-law function with a very hard photon index (Γ = 1.42 ± 0.1 stat ± 0.06 syst ) in the 0.1-500 GeV range and an energy flux above 100 MeV of (2.91 ± 0.8 stat ± 0.12 syst ) × 10 −11 erg cm −2 s −1 . Gathering all the available multiwavelength (MWL) data, we perform a broadband modeling of the nonthermal emission of RCW 86 to constrain parameters of the nearby medium and bring new hints about the origin of the γ-ray emission. For the whole SNR, the modeling favors a leptonic scenario in the framework of a two-zone model with an average magnetic field of 10.2 ± 0.7 µG and a limit on the maximum energy injected into protons of 2 × 10 49 erg for a density of 1 cm −3 . In addition, parameter values are derived for the North-East (NE) and South-West (SW) regions of RCW 86, providing the first indication of a higher magnetic field in the SW region. Subject headings: cosmic rays -ISM : individual objects (RCW 86) -acceleration of particles 1 Corresponding authors: M. Caragiulo,

Search for Extended Sources in the Galactic Plane Using Six Years of Fermi-Large Area Telescope Pass 8 Data above 10 GeV

“…This radius is larger than the disk size Figure 3 and identical references for the 2FHL and SNR catalogs. Left: SEDs of the extended sources with data points from this analysis (black stars and dashed butterfly), from the SNR catalog (purple line), from the 2FHL catalog (blue diamonds and line), from a previous Fermi-LAT publication (green triangles and line; Ajello et al 2016), and from IACT data (red triangles and line; Aharonian et al 2009, 2007b. Middle and right: background-subtracted TS maps using the same conventions as in Figure 3 and above-quoted references for the IACT contours shown in green.…”

“…White circles and central plus signs indicate the disk extension and centroid as fit in this work, respectively. In the top middle panel, the gray circle corresponds to the extension found in Ajello et al (2016).…”

Interstellar gas and X-rays toward the Young supernova remnant RCW 86; pursuit of the origin of the thermal and non-thermal X-ray

“…They noted the distribution of thin dust filaments in the east region, which appear to trace the SNR shockwaves. In contrast, neutral atomic gas (Hi) forms a cavity-like structure at radial velocities of approximately −34 km s −1 (Ajello et al 2016;Duvidovich et al 2016), although the detailed velocity structure and its relationship with the SNR shockwaves have not been presented.…”

“…INTRODUCTION RCW 86 (also known as MSH 14−63 or G315.4−2.3) is one of the supernova remnants (SNRs) that has been detected in the whole electromagnetic spectrum, from the radio continuum, optical, and infrared domains to the energetic X-rays and GeV/TeV γ-rays (e.g., Kesteven & Caswell 1987;Smith 1997;Williams et al 2011;Broersen et al 2014;Ajello et al 2016; H. E. S. S. Collaboration et al 2016). Of particular interest are the bright TeV γ-rays and nonthermal X-rays, which are tightly related with the production of cosmic-rays (CRs) via the diffusive shock acceleration (DSA) mechanism in SNRs (Bell 1978;Blandford & Ostriker 1978).…”

“…dataset and revealed the shelllike morphology in TeV γ-rays, the origin of which is not yet discerned. Most recently, Ajello et al (2016) obtained new GeV γ-ray images and spectra from a 6.5-year dataset of F ermi LAT. They concluded that the broad-band SED favors the leptonic origin under the two-zone model.…”