Dark Matter and Pulsar Model Constraints from Galactic Center Fermi-LAT Gamma Ray Observations (1306.5725v5)

Abstract: Employing Fermi-LAT gamma ray observations, several independent groups have found excess extended gamma ray emission at the Galactic center (GC). Both, annihilating dark matter (DM) or a population of $\sim 10^3$ unresolved millisecond pulsars (MSPs) are regarded as well motivated possible explanations. However, there is significant uncertainties in the diffuse galactic background at the GC. We have performed a revaluation of these two models for the extended gamma ray source at the GC by accounting for the systematic uncertainties of the Galactic diffuse emission model. We also marginalize over point source and diffuse background parameters in the region of interest. We show that the excess emission is significantly more extended than a point source. We find that the DM (or pulsars population) signal is larger than the systematic errors and therefore proceed to determine the sectors of parameter space that provide an acceptable fit to the data. We found that a population of order a 1000 MSPs with parameters consistent with the average spectral shape of Fermi-LAT measured MSPs was able to fit the GC excess emission. For DM, we found that a pure $\tau^+\tau^-$ annihilation channel is not a good fit to the data. But a mixture of $\tau^+\tau^-$ and $b\bar{b}$ with a $\left<\sigma v\right>$ of order the thermal relic value and a DM mass of around 20 to 60 GeV provides an adequate fit.

• The paper demonstrates that a millisecond pulsar population of around 1000 objects can accurately reproduce the observed gamma-ray excess.
• The research employs systematic adjustments to the Galactic diffuse emission model while marginalizing over point source contributions.
• The findings indicate that a mixed dark matter annihilation channel, with a mass between 20-60 GeV, provides a viable fit alongside pulsar models.

Analysis of Dark Matter and Pulsar Model Constraints from Gamma Ray Observations at the Galactic Center

The paper conducted by Gordon and Macias provides a thorough investigation of extended gamma-ray emission observed at the Galactic Center (GC), employing Fermi-LAT data to address the potential sources of this emission. The two primary hypotheses under scrutiny are annihilating dark matter (DM) and a population of unresolved millisecond pulsars (MSPs). The paper meticulously revisits these models while accounting for the significant uncertainties inherent in the Galactic diffuse background at the GC.

A key aspect of the research involves adjusting for systematic errors in the Galactic diffuse emission model, while simultaneously marginalizing over both the point source and diffuse background parameters within the region of interest. This methodical approach leads to a clearer understanding of the emission's extent and dismisses the possibility of it being attributed to a point source alone.

The paper offers substantial numerical evidence supporting the possible explanations for the observed gamma-ray excess. Notably, the analysis finds that the MSP model, with approximately 1000 MSPs, fits the GC excess emission, aligning well with Fermi-LAT measured MSPs. In contrast, for the DM scenario, a pure $\tau^+\tau^-$ annihilation channel is not adequate. Instead, a model consisting of a mixture of $\tau^+\tau^-$ and $b\bar{b}$ channels with a $\left<\sigma v\right>$ near the thermal relic value and a DM mass ranging between 20 to 60 GeV emerges as a viable fit.

Implications and Future Directions

The implications of these findings extend to both astrophysical and direct detection efforts. If the gamma-ray excess is attributed to MSPs, this would suggest a considerable population of such pulsars tightly packed within the GC, possibly shedding light on the dynamics and history of stellar evolution in such dense environments. Conversely, if DM annihilation is confirmed as the source, it would provide a critical clue towards identifying the particle nature of dark matter.

Furthermore, the research highlights the importance of creating robust models for Galactic diffuse emission, which remains a considerable source of uncertainty. As observational data proliferates, particularly with upcoming missions with higher sensitivity and angular resolution, it is expected that these uncertainties will reduce, leading to more definitive conclusions.

In the context of future developments, the paper suggests that continued improvements in gamma-ray observatory instruments, along with more refined modeling of Galactic dynamics and interstellar medium interactions, will enhance our understanding of extended gamma-ray sources in the GC. Additionally, this work underscores the potential for multi-messenger astrophysics, combining insights from gamma-ray, radio, and X-ray observations, to better constrain the characteristics and origins of Galactic phenomena.

Overall, the paper presents a compelling analysis that adds value to our understanding of gamma-ray emissions from the Galactic Center and sets a foundation for future investigations into the intersection of astrophysics and particle physics. The balance struck between systematic evaluation and model fitting reinforces the paper's credibility, paving the way for a deeper exploration of the Galactic Center's enigmatic nature.