Millisecond Pulsar Origin of the Galactic Center Excess and Extended Gamma-Ray Emission from Andromeda: A Closer Look

Eckner, Christopher; Hou, X.; Serpico, Pasquale Dario; Winter, Miles; Zaharijaš, Gabrijela; Martin, Pierrick; Mauro, Mattia Di; Mirabal, N.; Petrović, Jovana; Prodanovic, Tijana; Vandenbroucke, J.

doi:10.3847/1538-4357/aac029

Cited by 51 publications

(66 citation statements)

References 92 publications

Supporting

Mentioning

Contrasting

Order By: Relevance

“…Although our detailed morphological analysis does not seem to corroborate the luminosity fraction predicted by Ref. [85], we caution that a more direct comparison with that study is not at present possible given that the authors have assumed a spherically symmetric model (see Sec. 3 in [85]) for the distribution of the bulge stars.…”

Section: Discussioncontrasting

confidence: 88%

Strong evidence that the galactic bulge is shining in gamma rays

Macías

Horiuchi

Kaplinghat

et al. 2019

J. Cosmol. Astropart. Phys.

181

View full text Add to dashboard Cite

There is growing evidence that the Galactic Center Excess identified in the Fermi-LAT gamma-ray data arises from a population of faint astrophysical sources. We provide compelling supporting evidence by showing that the morphology of the excess traces the stellar over-density of the Galactic bulge. By adopting a template of the bulge stars obtained from a triaxial 3D fit to the diffuse near-infrared emission, we show that it is detected at high significance. The significance deteriorates when either the position or the orientation of the template is artificially shifted, supporting the correlation of the gamma-ray data with the Galactic bulge. In deriving these results, we have used more sophisticated templates at low-latitudes for the Fermi bubbles compared to previous work and the three-dimensional Inverse Compton (IC) maps recently released by the GALPROP team. Our results provide strong constraints on Millisecond Pulsar (MSP) formation scenarios proposed to explain the excess. We find that an admixture formation scenario, in which some of the relevant binaries are primordial and the rest are formed dynamically, is preferred over a primordial-only formation scenario at 7.6σ confidence level. Our detailed morphological analysis also disfavors models of the disrupted globular clusters scenario that predict a spherically symmetric distribution of MSPs in the Galactic bulge. For the first time, we report evidence of a high energy tail in the nuclear bulge spectrum that could be the result of IC emission from electrons and positrons injected by a population of MSPs and star formation activity from the same site. pulsars, in the form of either old "recycled" millisecond pulsars [13,18], or young pulsar remnants from Galactic Center supernovae [19,20]. The gamma-ray spectra of known pulsars are similar to the GCE, and the capture of pulsars onto the Galactic Center region by Globular Cluster disruptions could explain the GCE's quasi-spherical spatial distribution [21,22]. Other explanations for the GCE discussed in the literature include outbursts of cosmic-ray production by the central supermassive black hole (e.g., [23]).While pulsars are a natural astrophysical candidate, there is ongoing debate regarding the consistency of the luminosity function required to explain the GCE with that measured for the pulsar population observed elsewhere as point sources [24][25][26][27]. Nevertheless, there are strengthening indications that the GCE may have an astrophysical origin. Cosmic-ray interactions in the Galactic Center region are notoriously complex to model. New analyses have cast doubt on some of the main properties claimed previously for the GCE. First, the energy spectrum of the GCE is subject to large systematic uncertainties arising from the incomplete understanding of cosmic-ray interactions in the Galactic Center region (e.g., [13][14][15]17]). A variety of scenarios might, therefore, describe the GCE based on the energy spectrum alone. Second, it has been argued that the photon count distribution of the GCE is ...

show abstract

Section: Discussioncontrasting

confidence: 88%

Strong evidence that the galactic bulge is shining in gamma rays

Macías

Horiuchi

Kaplinghat

et al. 2019

J. Cosmol. Astropart. Phys.

181

View full text Add to dashboard Cite

show abstract

“…This emission resembles to some extent the well studied Galactic Center Excess (GCE) of gamma rays in the center of the Milky Way, and has led to comparisons in possible origins for the emission in the two galaxies. Proposed explanations for the GCE include signals of annihilating dark matter [13][14][15][16][17][18], an unresolved population of millisecond pulsars (MSP) [19][20][21], or additional cosmic-ray sources [22][23][24]. Due to some similarities between both the two galaxies themselves and the observed emissions, it is natural to also consider whether these are viable explanations for the M31 detection.…”

Section: Introductionmentioning

confidence: 99%

“…Additionally,the dark matter particle models in that analysis that can reproduce the M31 gamma-ray emission also produce synchrotron emission that is in tension with observational radio data. There have also been efforts made to explore a millisecond pulsar (MSP) explanation for the M31 gamma-ray emission [21,34]. Ref.…”

Section: Introductionmentioning

confidence: 99%

“…[34] studied MSPs originating from globular cluster disruption in the bulge of M31, whereas Ref. [21] considered MSPs formed in situ. The in situ model was found to fit the energetics and morphology of the excess well, however neither study could account for the full detected emission, with each providing only ∼ 1/4 of the M31 observation.…”

Section: Introductionmentioning

confidence: 99%

See 1 more Smart Citation

Exploring a cosmic-ray origin of the multiwavelength emission in M31

2019

View full text Add to dashboard Cite

A recent detection of spatially extended gamma-ray emission in the central region of the Andromeda galaxy (M31) has led to several possible explanations being put forth, including dark matter annihilation and millisecond pulsars. Another possibility is that the emission in M31 can be accounted for with a purely astrophysical cosmic-ray (CR) scenario. This scenario would lead to a rich multi-wavelength emission that can, in turn, be used to test it. Relativistic cosmic-ray electrons (CRe) in magnetic fields produce radio emission through synchrotron radiation, while X-rays and gamma rays are produced through inverse Compton scattering. Additionally, collisions of primary cosmic-ray protons (CRp) in the interstellar medium produce charged and neutral pions that then decay into secondary CRe (detectable through radiative processes) and gamma-rays. Here, we explore the viability of a CR origin for multi-wavelength emission in M31, taking into consideration three scenarios: a CR scenario dominated by primary CRe, one dominated by CRp and the resulting secondary CRe and gamma rays from neutral pion decay, and a final case in which both of these components exist simultaneously. We find that the multi-component model is the most promising, and is able to fit the multi-wavelength spectrum for a variety of astrophysical parameters consistent with previous studies of M31 and of cosmic-ray physics. However, the CR power injection implied by our models exceeds the estimated CR power injection from typical astrophysical cosmic-ray sources such as supernovae.

show abstract

“…Assuming that the same stellar populations responsible for the IR bulge trace the distribution of MSPs, a reasonable starting point for the MSP distribution is the bulge morphology itself. In principle, a proper morphological calculation would need to take into account the kick velocities of the MSP seeds at birth [48]. However, the kicks experienced by MSPs should be lower than for isolated pulsars, which is also necessary for them to be confined to globular clusters.…”

Section: A Stellar Modelsmentioning

confidence: 99%

Inverse Compton emission from millisecond pulsars in the Galactic bulge

2019

View full text Add to dashboard Cite

Analyses of Fermi Gamma-Ray Space Telescope data have revealed a source of excess diffuse gamma rays towards the Galactic center that extends up to roughly ±20 degrees in latitude. The leading theory postulates that this GeV excess is the aggregate emission from a large number of faint millisecond pulsars (MSPs). The electrons and positrons (e ± ) injected by this population could produce detectable inverse-Compton (IC) emissions by up-scattering ambient photons to gamma-ray energies. In this work, we calculate such IC emissions using GALPROP. A triaxial three-dimensional model of the bulge stars obtained from a fit to infrared data is used as a tracer of the putative MSP population. This model is compared against one in which the MSPs are spatially distributed as a Navarro-Frenk-White squared profile. We show that the resulting spectra for both models are indistinguishable, but that their spatial morphologies have salient recognizable features. The IC component above ∼TeV energies carries information on the spatial morphology of the injected e ± . Such differences could potentially be used by future high-energy gamma-ray detectors such as the Cherenkov Telescope Array to provide a viable multiwavelength handle for the MSP origin of the GeV excess.

show abstract

Millisecond Pulsar Origin of the Galactic Center Excess and Extended Gamma-Ray Emission from Andromeda: A Closer Look

Cited by 51 publications

References 92 publications

Strong evidence that the galactic bulge is shining in gamma rays

Strong evidence that the galactic bulge is shining in gamma rays

Exploring a cosmic-ray origin of the multiwavelength emission in M31

Inverse Compton emission from millisecond pulsars in the Galactic bulge

Contact Info

Product

Resources

About