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Abstract Pulsar halos are regions around middle-aged pulsars extending out to tens of parsecs. The large extent of the halos and well-defined central cosmic-ray accelerators make this new class of Galactic sources an ideal laboratory for studying cosmic-ray transport. LHAASO J0621+3755 is a candidate pulsar halo associated with the middle-aged gamma-ray pulsar PSR J0622+3749. We observed LHAASO J0621+3755 with VERITAS and XMM-Newton in the TeV and X-ray bands, respectively. For this work, we developed a novel background estimation technique for imaging atmospheric Cherenkov telescope observations of such extended sources. No halo emission was detected with VERITAS (0.3–10 TeV) or XMM-Newton (2–7 keV) within 1∘and around PSR J0622+3749, respectively. Combined with the LHAASO Kilometer Square Array (KM2A) and Fermi-LAT data, VERITAS flux upper limits establish a spectral break at ∼1–10 TeV, a unique feature compared with Geminga, the most studied pulsar halo. We model the gamma-ray spectrum and LHAASO-KM2A surface brightness as inverse Compton emission and find suppressed diffusion around the pulsar, similar to Geminga. A smaller diffusion suppression zone and harder electron injection spectrum than Geminga are necessary to reproduce the spectral cutoff. A magnetic field ≤1μG is required by our XMM-Newton observation and synchrotron spectral modeling, consistent with Geminga. Our findings support slower diffusion and lower magnetic field around pulsar halos than the Galactic averages, hinting at magnetohydrodynamic turbulence around pulsars. Additionally, we report the detection of an X-ray point source spatially coincident with PSR J0622+3749, whose periodicity is consistent with the gamma-ray spin period of 333.2 ms. The soft spectrum of this source suggests a thermal origin.
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This content will become publicly available on March 11, 2026
Upper Limits on GeV Gamma-Ray Flux from the Ultra-long Period Neutron Star PSR J0901−4046
Abstract PSR J0901−4046 is a radio neutron star with an ultra-long spin period of 75.88 s. We search 14 yr of Fermi-LAT observations for evidence of steady gamma-ray emission. We find no evidence of gamma-ray emission and set a 95% upper limit on the flux from PSR J0901−4046 of 1.4 × 10−9 photons cm−2s−1assuming a power law with exponential cutoff spectrum.
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- Award ID(s):
- 2411860
- PAR ID:
- 10621694
- Publisher / Repository:
- American Astronomical Society
- Date Published:
- Journal Name:
- Research Notes of the AAS
- Volume:
- 9
- Issue:
- 3
- ISSN:
- 2515-5172
- Page Range / eLocation ID:
- 53
- Subject(s) / Keyword(s):
- Gamma-ray astronomy Pulsars Gamma-rays Neutron stars Radio pulsars
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
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