Accretion-powered Pulsations in an Apparently Quiescent Neutron Star Binary
Deller, Adam T.; Lyne, Andrew G.; Bogdanov, Slavko; Tendulkar, Shriharsh P.; Hessels, Jason W. T.; Bassa, Cees; Wijnands, Rudy; Archibald, Anne M.; Janssen, Gemma H.; Patruno, Alessandro; Stappers, Ben W.; D'Angelo, Caroline R.; Kaspi, Vicky M.
Netherlands, United States, Canada, United Kingdom
Abstract
Accreting millisecond X-ray pulsars (AMXPs) are an important subset of low-mass X-ray binaries (LMXBs) in which coherent X-ray pulsations can be observed during occasional, bright outbursts (X-ray luminosity {L}{{X}}∼ {10}36 {erg} {{{s}}}-1). These pulsations show that matter is being channeled onto the neutron star’s magnetic poles. However, such sources spend most of their time in a low-luminosity, quiescent state ({L}{{X}}≲ {10}34 {erg} {{{s}}}-1), where the nature of the accretion flow onto the neutron star (if any) is not well understood. Here we report that the millisecond pulsar/LMXB transition object PSR J1023+0038 intermittently shows coherent X-ray pulsations at luminosities nearly 100 times fainter than observed in any other AMXP. We conclude that in spite of its low luminosity, PSR J1023+0038 experiences episodes of channeled accretion, a discovery that challenges existing models for accretion onto magnetized neutron stars.