THE SPECTRUM AND MORPHOLOGY OF THEFERMIBUBBLES

Abstract

The Fermi bubbles are two large structures in the gamma-ray sky extending to 55 • above and below the Galactic center. We analyze 50 months of Fermi Large Area Telescope data between 100 MeV and 500 GeV above 10 • in Galactic latitude to derive the spectrum and morphology of the Fermi bubbles. We thoroughly explore the systematic uncertainties that arise when modeling the Galactic diffuse emission through two separate approaches. The gamma-ray spectrum is well described by either a log parabola or a power law with an exponential cutoff. We exclude a simple power law with more than 7σ significance. The power law with an exponential cutoff has an index of 1.9 ± 0.2 and a cutoff energy of 110 ± 50 GeV. We find that the gamma-ray luminosity of the bubbles is 4.4 +2.4 −0.9 × 10 37 erg s −1. We confirm a significant enhancement of gamma-ray emission in the southeastern part of the bubbles, but we do not find significant evidence for a jet. No significant variation of the spectrum across the bubbles is detected. The width of the boundary of the bubbles is estimated to be 3.4 +3.7 −2.6 deg. Both inverse Compton (IC) models and hadronic models including IC emission from secondary leptons fit the gamma-ray data well. In the IC scenario, synchrotron emission from the same population of electrons can also explain the WMAP and Planck microwave haze with a magnetic field between 5 and 20 μG.

Multiwavelength features of Fermi bubbles as signatures of a Galactic wind

“…17 can be numerically integrated to give the resulting spectrum, which is shown in Figure 7. The spectrum shows a reasonable match with the spectra as observed by Su et al (2010) and Ackermann et al (2014). The figure also shows that the spectrum is consistent with the observations for γ b ranging from 5 × 10 5 to 2 × 10 6 and therefore Figure 7.…”

“…Output spectra for leptonic γ-ray emission (green dashed line). The blue empty squares and the magenta filled squares show the observed data points (Su et al 2010;Ackermann et al 2014), and the green (dashed) line shows the spectra calculated by us for γ b = 10 6 . The plot also shows the spectrum for γ b = 5 × 10 5 (blue dotted line) and γ b = 2 × 10 6 (red solid line) for comparison.…”

Studying the Interstellar Medium and the Inner Region of NPS/Loop 1 With Shadow Observations Toward Mbm36

“…In recent years, indeed, observations at different wavelengths have accumulated evidence in favor of a hypershell scenario. The Fermi bubbles (Dobler et al 2010;Su et al 2010; Ackermann et al 2014) are large-scale (order of some kpc) γ-ray features broadly overlapping Loop I. This region is also characterized by the WMAP haze in K-band microwaves (Finkbeiner 2004;Dobler & Finkbeiner 2008) and by polarized synchrotron radiation at 2.3GHz (Carretti et al 2013), in both cases showing biconical structures that can arise from an active Galactic Center.…”

The AGN Jet Model of the Fermi Bubbles

“…Alternatively, in the hadronic scenario, the gamma ray emission results from CR protons, which collide inelastically with the ambient gas and produce neutral pions, which decay into gamma rays (Crocker & Aharonian 2011, Zubovas et al 2011, Mou et al 2015. With properly chosen CR spectrum, both the leptonic and hadronic scenarios fit gamma ray data quite well, while the latter seems to require an extra population of primary electrons to explain the observed microwave emission from the Fermi bubbles (Ackermann et al 2014).…”

“…The Fermi bubbles are a large structure recently discovered in the inner Galaxy by the Fermi Gamma-ray Space Telescope (Su et al 2010, Dobler et al 2010, Ackermann et al 2014). The two gamma-ray bubbles have a bilobular shape, extending to ∼ 50 • above and below the Galactic center (GC).…”