Nature of Ultralong Period Radio Transients: Could They Be Strange Dwarf Pulsars?

Abstract

Ultralong period radio transients (ULPTs), with periods of thousands of seconds, challenge conventional pulsar models. We propose that these isolated sources are strange dwarf (SD) pulsars—compact objects with a strange quark matter core surrounded by a normal matter crust. We develop a theoretical framework for SD pulsars and apply it to four known isolated ULPTs: GLEAM-X J162759.5–523504.3, GPM J1839–10, ASKAP J1832–0911 (DART J1832–0911), and ASKAP J193505.1+214841.0 (ASKAP J1935+2148). Our analysis shows that SD pulsars naturally explain both the ultralong periods and coherent radio emission of these sources, which occupy a distinctive region in the magnetic field–period diagram. We find that these objects have surface magnetic fields ranging from 10 ^6 to 10 ^10 G, with a consistent lower bound near 10 ^6 G that suggests a fundamental threshold for pair production in these magnetospheres. Their radio emission efficiencies ( η _rad,rot ≈ 10 ^−4 –10 ^−2 ) align with those of normal pulsars despite their extreme periods. ASKAP J1935+2148 represents a boundary case, positioned below the theoretical death line but still radio active, offering crucial insights into emission mechanisms at extreme periods. The observed X-ray properties of ASKAP J1832–0911, including its two-component spectrum and synchronous X-ray/radio variability, strongly support the SD pulsar model. This framework provides a unified explanation for ULPTs and has significant implications for understanding exotic dense matter in compact objects.

Keywords

• Compact objects
• Pulsars
• Neutron stars
• Radio transient sources