The Andromeda gamma-ray excess: background systematics of the millisecond pulsars and dark matter interpretations

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dc.contributor.authorZimmer, Fabianen
dc.contributor.authorMacias, Oscaren
dc.contributor.authorAndo, Shin'ichiroen
dc.contributor.authorCrocker, Roland M.en
dc.contributor.authorHoriuchi, Shunsakuen
dc.date.accessioned2023-05-09T12:43:03Zen
dc.date.available2023-05-09T12:43:03Zen
dc.date.issued2022-09en
dc.description.abstractSince the discovery of an excess in gamma rays in the direction of M31, its cause has been unclear. Published interpretations focus on dark matter or stellar related origins. Studies of a similar excess in the Milky Way centre motivate a correlation of the spatial morphology of the signal with the distribution of stellar mass in M31. However, a robust determination of the best theory for the observed excess emission is challenging due to uncertainties in the astrophysical gamma-ray foreground model. We perform a spectro-morphological analysis of the M31 gamma-ray excess using state-of-the-art templates for the distribution of stellar mass in M31 and novel astrophysical foreground models for its sky region. We construct maps for the old stellar populations of M31 based on data from the PAndAS survey and carefully remove the foreground stars. We also produce improved astrophysical foreground models via novel image inpainting techniques based on machine learning methods. Our stellar maps, mimicking the location of a population of millisecond pulsars in the bulge of M31, reach a 5.4 sigma significance, making them as strongly favoured as the simple phenomenological models usually considered in the literature, e.g. disc-like templates. This detection is robust to generous variations of the astrophysical foreground model. Once the stellar templates are included in the astrophysical model, we show that the dark matter annihilation interpretation of the signal is unwarranted. We demonstrate that about one million unresolved millisecond pulsars naturally explain the observed gamma-ray luminosity per stellar mass, energy spectrum, and stellar bulge-to-disc flux ratio.en
dc.description.notesWe would like to thank Giuseppe Puglisi for all the help he provided with his inpainting package and Nicolas Martin for providing results from his previous works. We would also like to thank Ariane Dekker, Ebo Peerbooms, Sahaja Kanuri, and Manuel Loparco for fruitful discussions and their support. OM was supported by the GRAPPA Prize Fellowship. The work of SA was supported by JSPS/MEXT KAKENHI Grant Numbers JP17H04836, JP20H05850, and JP20H05861. The work of SH is supported by the U.S. Department of Energy under the award number DE-SC0020262, NSF Grant numbers AST1908960 and PHY-1914409, and JSPS KAKENHI Grant Number JP22K03630. This work was supported by World Premier International Research Center Initiative (WPI Initiative), MEXT, Japan.en
dc.description.sponsorshipGRAPPA Prize Fellowship; JSPS/MEXT KAKENHI [JP17H04836, JP20H05850, JP20H05861]; U.S. Department of Energy [DE-SC0020262]; NSF [AST1908960, PHY-1914409]; JSPS KAKENHI [JP22K03630]; World Premier International Research Center Initiative (WPI Initiative), MEXT, Japanen
dc.description.versionPublished versionen
dc.format.mimetypeapplication/pdfen
dc.identifier.doihttps://doi.org/10.1093/mnras/stac2464en
dc.identifier.eissn1365-2966en
dc.identifier.issue3en
dc.identifier.urihttp://hdl.handle.net/10919/114983en
dc.identifier.volume516en
dc.language.isoenen
dc.publisherOxford University Pressen
dc.rightsCreative Commons Attribution 4.0 Internationalen
dc.rights.urihttp://creativecommons.org/licenses/by/4.0/en
dc.subjectpulsars: generalen
dc.subjectdark matteren
dc.subjectgamma-rays: diffuse backgrounden
dc.titleThe Andromeda gamma-ray excess: background systematics of the millisecond pulsars and dark matter interpretationsen
dc.title.serialMonthly Notices of the Royal Astronomical Societyen
dc.typeArticle - Refereeden
dc.type.dcmitypeTexten

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