Low Mass X-Ray Binary Observations Challenge MSP Models of the Galactic Center Excess

Millisecond Pulsars have long been favored as a potential explanation for the excess gamma-ray emission surrounding the galactic center. However, the individual millisecond pulsars responsible for this emission have remained undetected -- a result that is not particularly unusual given their low individual luminosities. However, millisecond pulsars are expected to evolve through a prior low-mass x-ray binary state, which is often bright enough to be detected. We examing the low-mass x-ray binary population in the galactic center, comparing it to similar populations in globular clusters, finding that there are not enough low-mass x-ray binaries in the galactic center region to explain the extremely bright gamma-ray emission expected from their subsequent millisecond pulsar population.

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Low Metallicity Environments Produce a Brighter High-Mass X-Ray Binary Population

We study the effects of binary evolution on the production and emission of high-mass x-ray binaries. We find that there are two separate methods to produce extremely bright x-ray binary activity. The first is active primarily in high-metallicity environments, and is powered by the strong winds of supergiant OB stars which efficiently push material onto their binary companion. The second is active primarily in low-metallicity environemnts, as is powered by the production of tight binary orbits with efficient Roche Lobe Overflow producing mass transfer onto the compact object. The dominance of Roche Lobe Overflow at low metallicities is due to the small size of early-stage stars which allows binaries with small periods to form efficiently. The net effect is that more bright x-ray binaries are formed at low metallicities, increasing the x-ray luminosity of metal poor galaxies.

Full Publication List:

7. Low Mass X-Ray Binaries in the Inner Galaxy: Implications for MSPs and the GeV Excess
Daryl Haggard, Craig Heinke, Dan Hooper, Tim Linden
Journal of Cosmology and Astroparticle Physics 1705 05 056

6. On the Formation of Ultra-Luminous X-Ray Sources with NS Accretors: The Case of M82-X2
Tassos Fragos, Tim Linden, Vicky Kalogera, Panos Sklias
The Astrophysical Journal Letters, 802 2041

5. Ultraluminous X-Ray Sources in the Most Metal-Poor Galaxies
A. Prestwich, M. Tsantaki, A. Zezas, F. Jackson, T. Roberts, R. Foltz, Tim Linden, V. Kalogera
The Astrophysical Journal 769 2 92

4. Chandra Observations of the Collisional Ring Galaxy NGC 922
A. Prestwich, J. Galache, Tim Linden, V. Kalogera, A. Zezas, T. Roberts, R. Kilgard, A. Wolter, G. Trinchieri
The Astrophysical Journal, 747 2 150

3. On The Rarity of X-Ray Binaries with Naked Helium Donors
Tim Linden, Francesca Valsecchi, Vicky Kalogera
The Astrophysical Journal, 748 2 114

2. The Effect of Starburst Metallicity on Bright X-Ray Binary Formation Pathways
Tim Linden, Vicky Kalogera, Jeremy Sepinsky, Andrea Prestwich, Andreas Zezas, Jay Gallagher
The Astrophysical Journal, 725 2 1984

1. Probing Electron-Capture Supernovae: X-Ray Binaries in Starbursts
Tim Linden, Jeremy Sepinsky, Vicky Kalogera, Chris Belczynski
The Astrophysical Journal, 699 2 1573 (2009)

Tim Linden

Assistant Professor, Stockholm University