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ABSTRACT We present evidence for $$\gamma$$-ray emission from a stacked population of 39 high-latitude globular clusters (GCs) not detected in the Fermi Point Source Catalogue, likely attributable to populations of millisecond pulsars within them. In this work, we use 13 yr of data collected by the Large Area Telescope aboard the Fermi Gamma-Ray Space Telescope to search for a cumulative signal from undetected GCs and compared them to control fields (CFs), selected to match the celestial distribution of the target clusters so as to distinguish the $$\gamma$$-ray signal from background emission. The joint likelihood distribution of the GCs has a significant separation ($$\sim 4\sigma$$) from that of the CFs. We also investigate correlations between detected cluster luminosities and other cluster properties such as distance, the number of millisecond pulsars associated with each cluster, and stellar encounter rate but find no significant relationships. 

ABSTRACT Flares from magnetically active dwarf stars should produce relativistic particles capable of creating γ-rays. So far, the only isolated main-sequence star besides the Sun to have been detected in γ-rays is TVLM 513−46546. Detecting γ-ray flares from more dwarf stars can improve our understanding of their magnetospheric properties, and could also indicate a diminished likelihood of their planets’ habitability. In this work, we stack data from the Fermi Gamma-ray Space Telescope during a large number of events identified from optical and X-ray flare surveys. We report an upper limit of γ-ray emission from the population of flare stars. Stacking results towards control positions are consistent with a non-detection. We compare these results to observed solar γ-ray flares and against a model of emission from neutral pion decay. The upper limit is consistent with solar flares when scaled to the flare energies and distances of the target stars. As with solar flares, the neutral pion decay mechanism for γ-ray production is also consistent with these results. 

ABSTRACT We report on a likelihood-stacking search for γ-ray pulsars at 362 high-latitude locations that coincide with known radio pulsar positions. We observe a stacked signal conservatively 2.5σ over the background. Stacking their likelihood profiles in spectral parameter space implies a pulsar-like spectral index and a characteristic flux a factor of 2 below the Fermi Large Area Telescope point-source sensitivity, assuming isotropic/unbeamed emission from all sample pulsars. The same procedures performed on empty control fields indicate that the pulsars as a population can be distinguished from the background with a Δ(TS) = 28, where TS refers to test statistic, at the peak location (or 4.8σ), and the stacked spectra of the control fields are distinctly softer than those of the pulsars. This study also probes a unique region of parameter space populated by low $$\dot{E}$$ pulsars, most of which have no γ-ray ephemeris available, and is sensitive to high duty cycles. We also discuss the possible γ-ray emission mechanism from such pulsars.