NuSTAROBSERVATIONS AND BROADBAND SPECTRAL ENERGY DISTRIBUTION MODELING OF THE MILLISECOND PULSAR BINARY PSR J1023+0038

Abstract

We report the first hard X-ray (3-79 keV) observations of the millisecond pulsar (MSP) binary PSR J1023+0038 using NuSTAR. This system has been shown transiting between a low-mass X-ray binary (LMXB) state and a rotation-powered MSP state. The NuSTAR observations were taken in both LMXB state and rotation-powered state. The source is clearly seen in both states up to ∼ 79 keV. During the LMXB state, the 3-79 keV flux is about a factor of 10 higher that in the rotation-powered state. The hard X-rays show clear orbital modulation during the X-ray faint rotation-powered state but the X-ray orbital period is not detected in the X-ray bright LMXB state. In addition, the Xray spectrum changes from a flat power-law spectrum during the rotation-powered state to a steeper power-law spectrum in the LMXB state. We suggest that the hard X-rays are due to the intra-binary shock from the interaction between the pulsar wind and the injected material from the low-mass companion star. During the rotation-powered MSP state, the X-ray orbital modulation is due to Doppler boosting of the shocked pulsar wind. At the LMXB state, the evaporating matter of the accretion disk due to the gamma-ray irradiation from the pulsar stops almost all the pulsar wind, resulting the disappearance of the X-ray orbital modulation.

Discovery of a Redback Millisecond Pulsar Candidate: 3fgl J0212.1+5320

“…Although the folded X-ray lightcurve does not cover a full orbital cycle, the X-ray variation is likely periodic with an X-ray minimum around the inferior conjunction (Figure 1b). A similar phenomenon has been previously seen in the RB PSR J1023+0038 (Bogdanov et al 2011;Tendulkar et al 2014;Li et al 2014). From the Chandra data bins, the X-ray maximum occurs around the superior conjunction (i.e., φ 20 ∼ 0.5; observer-pulsarcompanion), although the Swift data favours the flux maximum around φ 20 > 0.5.…”

“…A few RBs, known as transitional MSPs, have already shown remarkable transition(s) between the LMXB state and the radio pulsar state in optical, X-rays, and/or γ-rays (i.e., M28I; Papitto et al 2013, PSR J1023+0038; Archibald et al 2009;Patruno et al 2014, and PSR J1227−4853; Roy et al 2015), clearly indicating the close relationship between LMXBs and radio MSPs. BW/RBs are interesting objects, not to mention the fascinating theoretical interpretation of multi-wavelength observations for individual studies (e.g., the keV-to-GeV emission models of PSR J1023+0038 in different states; Li et al 2014;Papitto & Torres 2015). They also pro-vide crucial information on the long-term accretion history.…”

“…As MSPs are powerful γ-ray sources with strong GeV magnetospheric radiations (e.g., from the outer gap, the slot gap, or the polar cap; Cheng et al 1986;Muslimov & Harding 2003;Ruderman & Sutherland 1975) and/or the inverse-Compton γ-ray emissions of the pulsar wind nebulae when the accretion is active Li et al 2014), many of them should have been detected by Fermi-LAT as a class of unidentified Fermi object (UFO), the second-largest population detected by Fermi-LAT (Acero et al 2015). Although not all the UFOs are MSPs (in fact many of them are thought to be AGNs, the largest source class in the catalog), good BW/RBs candidates can be selected based on the γ-ray spectral curvatures and the γ-ray variabilities (Ray et al 2012;Kong et al 2012Kong et al , 2014Hui et al 2015b) and confirmed their pulsar natures by detecting the radio/γ-ray pulsations.…”

Coordinated X-Ray, Ultraviolet, Optical, and Radio Observations of the PSR J1023+0038 System in a Low-Mass X-Ray Binary State

“…We do not find evidence for orbital modulation of the X-ray brightness during any of the three modes. Li et al (2014a) have reported evidence for periodicity at 3130 s in the NuSTAR data set of PSR J1023+0038. We have examined both XMM-Newton observations in search of a similar signal but find no evidence for it.…”

Gamma-ray pulsars: A gold mine

“…The J1023+0038 pulsar provides a useful test bed at a distance of 1.37 kpc toward the γ-ray source 2FGLJ1023.6+0040: an accretion disc was observed in the optical in 2000-2001; the detection of radio pulses from a MSP followed in 2007, until the pulses disappeared in 2013, quenched or eclipsed by the ionized flow from a new X-ray accretion disc [97,98,99]. The interaction between the pulsar magnetosphere/wind and the accretion disc is very dynamic, switching between different spectral states in X rays, with and without orbital modulation [98], and producing radio continuum emission and sporadic flares in the optical, UV, and X-rays, suggestive of propellor modes [97]. The γ-ray flux quintupled when the radio pulses disappeared [69,100].…”