Sizing up the population of gamma-ray binaries

Abstract

Gamma-ray binaries are thought to be composed of a young pulsar in orbit around a massive O or Be star, with their gamma-ray emission powered by pulsar spindown. The number of such systems in our Galaxy is not known. We aim to estimate the total number of gamma-ray binaries in our Galaxy and to evaluate the prospects for new detections in the GeV and TeV energy range, taking into account that their gamma-ray emission is modulated on the orbital period. We model the population of gamma-ray binaries and evaluate the fraction of detected systems in surveys with the Fermi-LAT (GeV), HESS, HAWC and CTA (TeV) using observation-based and synthetic template lightcurves. The detected fraction depends more on the orbit-average flux than on the lightcurve shape. Our best estimate for the number of gamma-ray binaries is 101${}_{-52}^{+89}$ systems. A handful of discoveries are expected by pursuing the Fermi-LAT survey. Discoveries in TeV surveys are less likely. However, this depends on the relative amounts of power emitted in GeV and TeV domains. There could be as many as $\approx$200 HESS J0632+057-like systems with a high ratio of TeV to GeV emission compared to other gamma-ray binaries. Statistics allow for as many as three discoveries in five years of HAWC observations and five discoveries in the first two years of the CTA Galactic Plane survey. Continued Fermi-LAT observations are favoured over ground-based TeV surveys to find new gamma-ray binaries. Gamma-ray observations are most sensitive to short orbital period systems with a high spindown pulsar power. Radio pulsar surveys (SKA) are likely to be more efficient in detecting long orbital period systems, providing a complementary probe into the gamma-ray binary population.

14 pages, 7 figures, submitted to A&A

References in corpus (5)

• VHE Gamma-Ray Observation of the Crab Nebula and its Pulsar with the MAGIC telescope
• HESS J0632+057 : A new gamma-ray binary?
• Periodic Emission from the Gamma-ray Binary 1FGL J1018.6-5856
• Multiwavelength monitoring and X-ray brightening of Be X-ray binary PSR J2032+4127/MT91 213 on its approach to periastron
• A Luminous Gamma-ray Binary in the Large Magellanic Cloud

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• Expectations for Fast Radio Bursts in Neutron Star-Massive Star binaries
• Fermi-LAT Observation of PSR B1259-63 during Its 2021 Periastron Passage
• New composite supernova remnant toward HESS J1844-030?
• A blazar as the likely counterpart to 4FGL J0647.7-4418 instead of a gamma-ray binary
• A Precessing Jet Scenario for the Multi-Wavelength Long-Term Modulation of LS I +61${}^{\circ }$303
• Possible TeV $\gamma$-ray binary origin of HESS J1828-099
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• Orbital Phase-resolved Analysis of X-ray and Gamma-ray Observations of the High-Mass Gamma-ray Binary 4FGL J1405.1-6119