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

Abstract

A new measurement of a spatially extended gamma-ray signal from the center of the Andromeda galaxy (M31) has recently been published by the Fermi-LAT collaboration, reporting that the emission broadly resembles the so-called Galactic center excess (GCE) of the Milky Way (MW). The weight of the evidence is steadily accumulating on a millisecond pulsar (MSPs) origin for the GCE. These elements prompt us to compare these observations with what is, perhaps, the simplest model for an MSP population, which is solely obtained by rescaling of the MSP luminosity function that is determined in the local MW disk via the respective stellar mass of the systems. Remarkably, we find that without free fitting parameters, this model can account for both the energetics and the morphology of the GCE within uncertainties. For M31, the estimated luminosity due to primordial MSPs is expected to only contribute about a quarter of the detected emission, although a stronger contribution cannot be excluded given the large uncertainties. If correct, the model predicts that the M31 disk emission due to MSPs is not far below the present upper bound. We also discuss additional refinements of this simple model. Using the correlation between globular cluster gamma-ray luminosity andmore » stellar encounter rate, we gauge the dynamical MSP formation in the bulge. This component is expected to contribute to the GCE only at a level of ≲5%, it could affect the signal's morphology. In conclusion, we also comment on the limitations of our model and on future perspectives for improved diagnostics.« less

Authors:

Eckner, Christopher ^[1]; Hou, Xian  ^[2];

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Serpico, Pasquale D. ^[3]; Winter, Miles  ^[4];

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Zaharijas, Gabrijela ^[5]; Martin, Pierrick ^[6]; Mauro, Mattia di ^[7]; Mirabal, Nestor  ^[8];

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Petrovic, Jovana ^[9]; Prodanovic, Tijana  ^[9];

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Vandenbroucke, Justin  ^[3]

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+ Show Author Affiliations

1. Univ. of Nova Gorica, Nova Gorica (Slovenia)
2. Chinese Academy of Sciences, Kunming (People's Republic of China); Chinese Academy of Sciences, Beijing (People's Republic of China)
3. Univ. Savoie Mont Blanc & CNRS, Annecy Cedex (France)
4. Univ. of Wisconsin, Madison, WI (United States)
5. Univ. of Nova Gorica, Nova Gorica (Slovenia); Instituto Nazionale di Fisica Nucleare - Sezione Trieste, Trieste (Italy)
6. Univ. Paul Sabatier, Toulouse Cedex (France)
7. Stanford Univ., Stanford, CA (United States)
8. Univ. of Maryland Baltimore County (UMBC), Baltimore, MD (United States); NASA Goddard Space Flight Center (GSFC), Greenbelt, MD (United States)
9. Univ. of Novi Sad, Novi Sad (Serbia)

Publication Date:

2018-07-25

Research Org.:

SLAC National Accelerator Lab., Menlo Park, CA (United States)

Sponsoring Org.:

USDOE

OSTI Identifier:

1468959

Grant/Contract Number:  

AC02-76SF00515

Resource Type:

Accepted Manuscript

Journal Name:

The Astrophysical Journal (Online)

Additional Journal Information:

Journal Name: The Astrophysical Journal (Online); Journal Volume: 862; Journal Issue: 1; Journal ID: ISSN 1538-4357

Publisher:

Institute of Physics (IOP)

Country of Publication:

United States

Language:

English

Subject:

79 ASTRONOMY AND ASTROPHYSICS; gamma rays: galaxies; Local Group; pulsars: general