Multiwavelength Pulsations and Surface Temperature Distribution in the Middle-aged Pulsar B1055–52

Journal article

We present a detailed study of the X-ray emission from PSR B1055–52 using XMM-Newton observations from 2019 and 2000. The phase-integrated X-ray emission from this pulsar is poorly described by existing models of neutron star atmospheres. Instead, we confirm that, similar to other middle-aged pulsars, the best-fitting spectral model consists of two blackbody components, with substantially different temperatures and emitting areas, and a nonthermal component characterized by a power law. Our phase-resolved X-ray spectral analysis using this three-component model reveals variations in the thermal emission parameters with the pulsar’s rotational phase. These variations suggest a nonuniform temperature distribution across the neutron star’s surface, including the cold thermal component and probable hot spot(s). Such a temperature distribution can be caused by external and internal heating processes, likely a combination thereof. We observe very high pulse fractions, 60%–80% in the 0.7–1.5 keV range, dominated by the hot blackbody component. This could be related to temperature nonuniformity and potential beaming effects in an atmosphere. We find indication of a second hot spot that appears at lower energies (0.15–0.3 keV) than the first hot spot (0.5–1.5 keV) in the X-ray light curves and is offset by about half a rotation period. This finding aligns with the nearly orthogonal rotator geometry suggested by radio observations of this interpulse pulsar. If the hot spots are associated with polar caps, a possible explanation for their temperature asymmetry could be an offset magnetic dipole and/or an additional toroidal magnetic field component in the neutron star crust.

Authors: Vahdat, A; Posselt, B; Pavlov, GG; Weltevrede, P; Santangelo, A

• Publication status: Published
• Peer review status: Peer reviewed
• Publisher: American Astronomical Society
• Journal: The Astrophysical Journal
• Volume: 963
• Issue: 2
• Article number: 138
• Publication date: 2024-03-07
• Acceptance date: 2024-01-19
• DOI: 10.3847/1538-4357/ad20ca
• EISSN: 1538-4357
• ISSN: 0004-637X
• Language: English
• Keywords: High energy astrophysics; X-ray astronomy; Compact objects; Pulsars; Neutron stars