Discrepancies in the Spectra of the Pulse-on and the Pulse-off Stages of Intermittent Accreting Millisecond X-ray Pulsars

Güngör C., Kocabiyik T., Saglam M. T.

44th COSPAR Scientific Assembly. Held 16-24 July, Athens, Greece, 16 July 2022, vol.44, pp.2383

  • Publication Type: Conference Paper / Summary Text
  • Volume: 44
  • City: Athens
  • Country: Greece
  • Page Numbers: pp.2383
  • Erciyes University Affiliated: No


Low Mass X-ray Binaries (LMXBs) are the binary systems in which one of the companion is a low mass star and the other is a compact object, a black hole or a neutron star (NS). The spin frequencies of the NSs associated with LMXBs have not yet been detected in most of the systems due to lack of pulsations. The possible reasons behind the absence of pulsations can be summarized as the following; (i) The magnetic field of the compact object might be too weak to canalize the material in the inner radius of the disk through the pole of the NS. (ii) Gravitational lensing effect could blur the illumination from the polar caps then the amplitude of the signals could decrease to the undetectable levels. (iii) The periodic changes in the flux could be annihilated as a result of that X-ray light is upscattered from the comptonized coronae. Accreting Millisecond X-ray Pulsars (AMXPs) constitute a subclass of LMXBs showing periodic signals in their X-ray light curve. In a branch of this subclass, so called Intermittent--AMXPs, the pulsations are not persistent. There are three Intermittent sources discovered upto now; SAX J1748.9-2021, Aql X-1 and HETE J1900.1-2455. These peculiar sources show both pulse-on and pulse-off stages and are exclusive to study pulse phenomena in LMXBs. In this research, we present a detailed spectral analysis in the pulse-on and pulse-off stages of Intermittent-AMXPs by using the Rossi X-ray Timing Explorer data. We discuss the similarities and discrepancies in the physical parameters obtained throughout our analysis during different pulse episodes for a specific source. We argue our results in the framework of different flux and hardness levels.