THE FERMI HAZE: A GAMMA-RAY COUNTERPART TO THE MICROWAVE HAZE

“A schematic of the relative importance of these emission mechanisms in the Galactic plane (|ℓ| ≤ 30, |b| ≤ 5) generated by the GALPROP code, version 50p (Strong et al. 2000; Porter & Strong 2005; Strong et al. 2007) is shown in Figure 2.”

“Examining known point source populations (of AGN and X-ray binaries) generally yields spectral indices α ∼ 1.5−2.2, although at high luminosities steeper power laws with α ∼ 2.5 have been observed in flat spectrum radio quasars, and at low luminosities very shallow power laws with α ∼ 1.2 have been measured in LMXB po…”

“A schematic of the relative importance of these emission mechanisms in the Galactic plane (|ℓ| ≤ 30, |b| ≤ 5) generated by the GALPROP code, version 50p (Strong et al. 2000; Porter & Strong 2005; Strong et al. 2007) is shown in Figure 2.”

“…power laws with α ∼ 2.5 have been observed in flat spectrum radio quasars, and at low luminosities very shallow power laws with α ∼ 1.2 have been measured in LMXB populations (Grimm et al. 2003; Gilfanov 2004; Kim & Fabbiano 2004; Voss & Gilfanov 2006; Padovani et al. 2007; Abdo et al. 2009a).”

“…power laws with α ∼ 2.5 have been observed in flat spectrum radio quasars, and at low luminosities very shallow power laws with α ∼ 1.2 have been measured in LMXB populations (Grimm et al. 2003; Gilfanov 2004; Kim & Fabbiano 2004; Voss & Gilfanov 2006; Padovani et al. 2007; Abdo et al. 2009a).”

“Previous studies of high latitude gamma-ray emission have reported measurements of an excess of emission above the Galactic plane, most notably SAS2 (Fichtel et al. 1975; Kniffen & Fichtel 1981), COS-B (Strong 1984), and EGRET (Smialkowski et al. 1997; Dixon et al. 1998).”

“…which roughly matches the microwave haze (i.e., centered on the GC, roughly spherical, and about 20-40◦ in radius), we now attempt to remove the π0 emission from the maps shown in Figure 1, using the same template fitting technique used in Finkbeiner (2004a) and Dobler & Finkbeiner (2008).”

“The LAT (Large Area Telescope) on Fermi (see Gehrels & Michelson 1999 as well as the Fermi homepage9) is a pair-conversion telescope consisting of 16 layers of tungsten on top of a calorimeter with a thickness of 7 radiation lengths.”

“Here the 41 GHz synchrotron (haze plus Haslam-correlated emission, see Haslam et al. 1982; Dobler & Finkbeiner 2008) is shown side by side with the 5-10 GeV Fermi residual map with the mask used in the Dobler & Finkbeiner (2008) microwave analysis overlaid for visualization.”

“…power laws with α ∼ 2.5 have been observed in flat spectrum radio quasars, and at low luminosities very shallow power laws with α ∼ 1.2 have been measured in LMXB populations (Grimm et al. 2003; Gilfanov 2004; Kim & Fabbiano 2004; Voss & Gilfanov 2006; Padovani et al. 2007; Abdo et al. 2009a).”

“We normalize the synchrotron to the approximate value measured by WMAP in the 23 GHz K-band (Hooper et al. 2007), ∼ 15◦ below the Galactic plane, and compute the corresponding synchrotron and IC spectra.”

“7 See http://fermi.gsfc.nasa.gov/ssc/data/ 2 Cholis et al. (2009a); Zhang et al. (2009); Borriello et al. (2009); Cirelli & Panci (2009); Regis & Ullio (2009); Belikov & Hooper (2009); Meade et al. (2009).”

“7 See http://fermi.gsfc.nasa.gov/ssc/data/ 2 Cholis et al. (2009a); Zhang et al. (2009); Borriello et al. (2009); Cirelli & Panci (2009); Regis & Ullio (2009); Belikov & Hooper (2009); Meade et al. (2009).”

“…power laws with α ∼ 2.5 have been observed in flat spectrum radio quasars, and at low luminosities very shallow power laws with α ∼ 1.2 have been measured in LMXB populations (Grimm et al. 2003; Gilfanov 2004; Kim & Fabbiano 2004; Voss & Gilfanov 2006; Padovani et al. 2007; Abdo et al. 2009a).”

“7 See http://fermi.gsfc.nasa.gov/ssc/data/ 2 Cholis et al. (2009a); Zhang et al. (2009); Borriello et al. (2009); Cirelli & Panci (2009); Regis & Ullio (2009); Belikov & Hooper (2009); Meade et al. (2009).”

“This field strength is appropriate for an exponential model for the Galactic B-field intensity, |B| = |B0|e−z/zs , with B0 ≈ 20 − 30µG (which seems reasonable; see e.g. Ferriere (2009) and references therein) and scale height zs ≈ 2 kpc (the default value in GALPROP).”

“Although it is still possible that a significant fraction is prompt photons from WIMP annihilations (e.g. the 200 GeV wino advocated by Grajek et al. 2009) such explanations are difficult to reconcile with the spatial similarity to the WMAP haze (see Figure 4).”

“Previous studies of high latitude gamma-ray emission have reported measurements of an excess of emission above the Galactic plane, most notably SAS2 (Fichtel et al. 1975; Kniffen & Fichtel 1981), COS-B (Strong 1984), and EGRET (Smialkowski et al. 1997; Dixon et al. 1998).”

“The prominent North Polar spur feature in the Haslam map, which is thought to originate from synchrotron emission from electrons in Loop I (Large et al. 1962), is over-subtracted in each case, because the North Polar spur is brighter in the Haslam map than in the gamma-ray maps (i.e. the ratio of…”

“7 See http://fermi.gsfc.nasa.gov/ssc/data/ 2 Cholis et al. (2009a); Zhang et al. (2009); Borriello et al. (2009); Cirelli & Panci (2009); Regis & Ullio (2009); Belikov & Hooper (2009); Meade et al. (2009).”

“7 See http://fermi.gsfc.nasa.gov/ssc/data/ 2 Cholis et al. (2009a); Zhang et al. (2009); Borriello et al. (2009); Cirelli & Panci (2009); Regis & Ullio (2009); Belikov & Hooper (2009); Meade et al. (2009).”

“Consequently, there have been concerns (Linden & Profumo 2010) that this template-based analysis might introduce spurious large-scale residuals.”

“However, in each case the experiments either covered an insufficient energy range (SAS-2 and COS-B) or did not have sufficient sensitivity and angular resolution (EGRET) to permit a spatial correlation with the WMAP haze.”

“However, in each case the experiments either covered an insufficient energy range (SAS-2 and COS-B) or did not have sufficient sensitivity and angular resolution (EGRET) to permit a spatial correlation with the WMAP haze.”

“One interesting possibility characterizes the haze as a separate hard spectrum synchrotron component associated with the Gammaray bubbles (Planck Collaboration IX 2012; Dobler et al. 2010).”

“As in Dobler et al. (2010), we construct maps of front-converting and back-converting events separately, smooth to a common PSF, and then combine them.”

“Dobler et al. (2010) and Su et al. (2010) have noted the existence of large-scale structures of residual diffuse γ-ray emission above and below the Galactic center region that became well known as the ‘Fermi Bubbles’.”

“Interesting features were identified in the spectrum of γrays originating from regions around the GC in the WMAP data [341] (so-called WMAP haze), Fermi-LAT data [342, 343] (Fermi bubbles) and Planck data [344] (Planck haze), with a possible common origin.”

“Fermi9 also recently detected bubbles of a similar scale in our Galaxy, clearly originating from the Galactic Center (Dobler et al. 2010; Su et al. 2010).”

“Moreover, the analysis of gamma-ray data has led to the discovery of the Fermi bubbles [23, 24], which are believed to be the inverse Compton scattering (ICS) counterpart [23] of the WMAP haze [25, 26], recently observed also with Planck [27].”

“Long before the Fermi discovery of two giant ∼ 12-kpc 1-100 GeV γ-ray emitting bubbles extending ∼ 55◦ on either side of the Galactic center (Fig. 9a; Su et al. 2010; Dobler et al. 2010; Ackermann et al. 2014) and the earlier discovery of a microwave “haze” in the data from the Wilkinson Microwave Anisotropy Probe (WM…”

“[68]).”

“…Salam International Center for Theoretical Physics, Strada Costiera 11, Trieste 34151 - Italy Gamma-ray lobes, called the Fermi bubbles, were discovered (Dobler et al. 2010; Su et al. 2010; Su & Finkbeiner 2012) in a search for a gamma-ray counterpart to the Wilkinson Microwave Anisotropy Probe…”

“erized, an interesting morphological structure has come to light in recent analysis of the data. After subtracting out templates for the neutral pion, inverse Compton, and 74 bremsstrahlung emission, Dobler et al. (2010) rst reported a detection of the \Fermi Haze," which extends 50above and below the Galactic pl…”

“For the latter, gamma rays can be produced by the inverse Compton (IC) scattering of CR electrons with the interstellar radiation field (ISRF) and the cosmic microwave background (CMB; Dobler et al. 2010, Su et al. 2010).”

“One of the most unexpected findings of the Fermi-LAT mission was the discovery of the ‘Fermi bubbles’ [224, 225, 226].”

“One of the most important findings from the first two years of Fermi Gamma-ray Space Telescope observations are two large bubbles extending to ∼ 50◦ above and below the Galactic center (GC), with a width of ∼ 40◦ in longitude (Su et al. 2010; Dobler et al. 2010).”

“A detection of a gamma-ray excess towards the Galactic center region in the gamma-ray data obtained with the Fermi satellite was recently reported in [ 56 ], and has been dubbed the \Fermi haze".”

“Similarly, analysis of Fermi -LAT data has led to claims of a corresponding gamma-ray haze, described as the high-energy counterpart to the WMAP haze (Dobler et al., 2010) and produced by IC scattering of electrons and positions on the ISRF.”

“While the physical distance to the Galactic Center is given in kilo-parsecs (kpc; one parallactic seconds or 1 pc = 3.09×1016 m) the physical scales at the Center are given in light years (ly = 9.46×1015 m) or parsecs (parallactic seconds or 1 pc = 3.3 ly) or fractions thereof, i.e., milli-parsecs (mpc) of micro-parse…”

“The existence of an anomalous microwave “haze” (in the WMAP data) coinciding with gamma-ray bubbles (in the Fermi-LAT data) centered around the GC has been largely debated and remains a controversial issue ([213, 158].”

“…GC (≈12 kpc) and show enhanced emission across the electromagnetic spectrum, including: (1) γ-ray emission, i.e. the Fermi Bubbles (FBs; Su et al. 2010; Dobler et al. 2010; Ackermann et al. 2014); (2) soft X-ray emission (0.3–1.0keV; Snowden et al. 1997; Kataoka et al. 2013); (3) K-band microwave…”

“A recent study by Dobler et al. (2011) also suggests that annihilating DM with similarly low masses (mDM = 1−20 GeV) may give a good match to the observed Fermi and WMAP haze (Dobler et al. 2010; Dobler & Finkbeiner 2008).”

“5.4 Explaining the WMAP ‘haze’ and Fermi ‘bubbles’ From detailed morphological and spectral analysis of large angular scale maps of microwave and ∼GeV γ-ray emission produced, respectively, by the WMAP and Fermi instruments, Finkbeiner and co-workers (Finkbeiner 2004; Dobler & Finkbeiner 2008; Dobler et al. 2010; Su e…”

“The Fermi bubbles are enigmatic, giant γ-ray structures emanating north and south from the nucleus of the Milky Way (Dobler et al. 2010; Su et al. 2010; Su & Finkbeiner 2012; Ackermann et al. 2014; Yang et al. 2014) and extending to heights above the Galactic plane approaching 8 kpc. Features…”

“Recent analysis of Fermi/LAT data (see Su et al. 2010; Dobler et al. 2010) discovered new evidence of GC activity.”

“Intensity, spatial and spectral correlations between the gamma-ray and microwave signals have been shown to support this hypothesis [6, 41, 44, 47].”

“…source types (e.g., Nolan et al. 2012), yet another important LAT discovery concerns the large-scale γ -ray structure, the so-called Fermi Bubbles, extending for about 50◦ (or 8.5 kpc) above and below the Galactic center (GC), with a longitudinal width of ∼40◦ (Dobler et al. 2010; Su et al. 2010).”

“by Finkbeiner (2004), Dobler & Finkbeiner (2008a) and Planck Collaboration Int.”

“It accounts also for large-scale structures such as the North Polar Spur (Haslam et al. 1981), the so-called Fermi bubbles (Su, Slatyer & Finkbeiner 2010; Dobler et al. 2010; Ackermann et al. 2014), and the Earth’s Limb emission.”

“The Fermi Bubbles (FBs) (Dobler et al. 2010; Su et al. 2010) are giant 1-100 GeV, γ ray emitting structures that extend up to ≈ ±55◦ above and below the Galactic Center.”

“…on the sky, their gamma-ray spectrum follows a power law with dN/dE ∝ E−2 between ≈1 and 200 GeV, and they have a counterpart in microwaves, known as the Wilkinson Microwave Anisotropy Probe (WMAP ) haze (Dobler & Finkbeiner 2008; Dobler et al. 2010; Su et al. 2010; Ackermann et al. 2014).”

“One interpretation is that the gamma-ray photons arise through inverse Compton scattering of the interstellar and cosmic background radiation field by high energy cosmic rays (10−100 GeV) from the black hole accretion disk (Su et al 2010; Dobler et al 2010).”

“This prediction is consistent with the detection of the inverse Compton component of the WMAP haze, the Fermi haze, and its spectrum (Dobler et al. 2010; Su et al., 2010).”

“One of the most interesting recent discoveries in high-energy astronomy is of the ‘Fermi bubbles’ (Dobler et al. 2010; Su et al. 2010) introduced earlier.”

“s have been identied from the Galactic Center toward the halo, so in the direction perpendicular to the Galactic disk. The so-called WMAP haze was discovered rst [221], followed by the Fermi-bubbles [430, 192]. These two features, the rst at microwave and the second at GeV energies, respectively, have been shown to ha…”

“It is yet unclear if the gamma ray emission from the Fermi bubbles is dominated by CR electrons or protons (Dobler et al. 2010; Crocker & Aharonian 2011).”

“The standard strategy is either to use templates (Dobler et al. 2010) that trace the sources or else to simulate the cosmic-ray propagation and gamma-ray production using, e.g., Galprop (Strong et al. 2007, 2009).”

“The Fermi Bubbles are more evidence for powerful phenomena in the Galactic Centre (Finkbeiner 2004; Dobler et al. 2010; Su, Slatyer, & Finkbeiner 2010 (S10); Planck Collaboration 2013).”

“FERMI-LAT observations have revealed two giant gamma-ray bubbles extending to a Galactic latitude of 50◦, and containing an energy of 1054−1055 erg (Dobler et al. 2010; Su et al. 2010).”

“The synchrotron nature of the microwave haze was substantially supported by the discovery of a gamma-ray counterpart to this emission by Dobler et al. (2010) using data from the Fermi Gamma-ray Space Telescope.”

“[45] suggested the Fermi Lobes (bubbles/haze) [47] as cause for the observed signature; but this possibility was however quickly disputed by ref.”

“…black hole (SMBH) (Ghez et al. 2008; Gillessen et al. 2009), which may have been active as recently as 10 Myr ago, if the giant Fermi bubbles (Dobler et al. 2010; Su et al. 2010) are interpreted as resulting from a black hole accretion event; it is rich in massive young stars (Bartko et al.…”

“Also, similar distribution can produce radio emission in the galaxy [110, 114] due to the synchrotron radiation effect with the interaction of microgauss galactic magnetic field.”

“Other signatures that have been associated with Galactic dark matter annihilation include the WMAP haze (Hooper et al 2007), a diffuse radio emission that could be related to electrons and positrons produced by dark matter and possibly a gammaray haze (Dobler et al 2010).”

“Of particular interest is the WMAP/Planck haze (Planck Collaboration IX 2013), identified as excess emission at ≈1 cm partly coincident with the Fermi γ -ray bubbles (Dobler et al. 2010; Ackermann et al. 2014) that appear to delineate a 10-kpc scale bipolar outflow from the Galactic centre.”

“Discovered in 2010 by [102] in a search for a gamma-ray counterpart to the WMAP4 haze (see e.”

“A wide variety of objects have been targeted, including the Galactic center (e.g. Abdo et al. 2010a; Dobler et al. 2010; Abazajian & Harding 2012; Abazajian & Kaplinghat 2012; Weniger 2012), the diffuse Galactic and extragalactic backgrounds (Abdo et al. 2010c; Cirelli et al. 2010; Papucci &…”

“However, this model has been almost ignored until the launch of the Fermi gamma-ray space telescope [17-19].”

“…been proposed that this spherical distribution of a population of hot electrons has been created by some large episode of energy injection in the Galactic center over the past 10Myr by either a period of activity of our supermassive black hole or a dramatic nuclear starburst (Dobler et al. 2010).”

“It is interesting to comment in this context on the similarities between the Circinus lobes and the FermiLAT discovered giant ‘Fermi Bubbles’ in our Galaxy (Dobler et al. 2010; Su et al. 2010).”

“Finally, the bubble structure on the Galactic scale has also been shown in the Fermi-LAT data (Dobler et al. 2010; Su et al. 2010; Su & Finkbeiner 2012; Yang et al. 2014; Ackermann et al. 2014).”

“Since the haze/bubbles was first discovered in the microwaves by Finkbeiner (2004a), and especially since the recent discovery in the gammas by Dobler et al. (2010), there has been significant effort devoted to theorizing about the origin of this hard spectrum population of electrons.”

“They are observed as hardspectrum gamma-ray structures (Su et al. 2010; Dobler et al. 2010) which coincide with radio lobes (Carretti et al. 2013).”

“′3 Full-sky WMAP 9-yre . . . . . . . . . . . . . . . . . . 93.5 14.”

“Fermi bubbles are huge gamma ray bubbles discovered with Fermi Gamma-ray Space Telescope in the direction of the Galactic center (GC) in the GeV band (Su et al. 2010; see also Dobler et al. 2010).”

“Given the above rate, this implies that supernovae inject ∼1039 erg s−1 into the GC CR population (cf. Crocker & Aharonian 2010).”

“…template fitting techniques to morphologically regress out the emission from π0’s, bremsstrahlung, and IC from disk electrons from the Fermi maps, Dobler et al. (2010) found an excess “haze” of IC emission towards the Galactic center (GC) extending ±50 degrees in latitude and with an axis…”

“The Fermi Bubbles are largely extended GeV gamma ray sources of ∼ 50◦ above and below the GC (Dobler et al. 2010; Su et al. 2010).”

“[41] was that more than 90% of the DGE at all sky locations and all investigated energies could be accounted for by a simple, phenomenologically constructed two component model: The γ-ray spectra of a molecular cloud complex in the Galactic anti-center and that of the southern tip of the southern Fermi bubble [45–47]…”

“The “Fermi bubbles” are giant gamma-ray structures extending above and below the Galactic center (GC) for about 8 kpc (Dobler et al. 2010; Su et al. 2010; Ackermann et al. 2014).”

“Excess γ -rays in the Fermi satellite (Abdo et al. 2009a,b; Dobler et al. 2010; The Fermi LAT Collaboration 2011) may be due to DM annihilation, and annual modulation (Drukier, Freese & Spergel 1986; Freese, Frieman & Gould 1988) in direct detection experiments DAMA (Bernabei et al. 2010) and…”

“Two giant gamma-ray bubbles above and below the Galactic plane were discovered by the Fermi Gammaray Space Telescope (Su et al. 2010; Dobler et al. 2010).”

“For instance, the microwave haze —produced by synchrotron radiation— can help to constrain the electron population, which can also radiate in gamma rays (Dobler et al. 2010; Su et al. 2010; Crocker & Aharonian 2011; Mou et al. 2015; Guo et al. 2012).”

“To that end, the method which is described in [60] is followed.”

“There are evidences of past activities (Sunyaev et al. 1993; Koyama et al. 1996; Dobler et al. 2010; Su et al. 2010), where the luminosity had reached as high as ∼ 1040 erg s−1.”

“Two huge, bubble-like structures have been reported by Su et al. (2010), Dobler et al. (2010), and Su & Finkbeiner (2012) in Fermi-LAT gamma-ray data to extend ∼50◦ above and below the Galactic center.”

“The first indication of the structure appeared in a paper by Dobler et al. (2010), which they called the Fermi Haze.”