Pulsating in Unison at Optical and X-Ray Energies: Simultaneous High Time Resolution Observations of the Transitional Millisecond Pulsar PSR J1023+0038

Abstract

PSR J1023+0038 is the first millisecond pulsar discovered to pulsate in the visible band; such a detection took place when the pulsar was surrounded by an accretion disk and also showed X-ray pulsations. We report on the first high time resolution observational campaign of this transitional pulsar in the disk state, using simultaneous observations in the optical (TNG, NOT, TJO), X-ray (XMM-Newton, NuSTAR, NICER), infrared (GTC) and UV (Swift) bands. Optical and X-ray pulsations were detected simultaneously in the X-ray high intensity mode in which the source spends ∼ 70% of the time, and both disappeared in the low mode, indicating a common underlying physical mechanism. In addition, optical and X-ray pulses were emitted within a few km, had similar pulse shape and distribution of the pulsed flux density compatible with a power-law relation F ν ∝ ν −0.7 connecting the optical and the 0.3-45 keV X-ray band. Optical pulses were detected also during flares with a pulsed flux reduced by one third with respect to the high mode; the lack of a simultaneous detection of X-ray pulses is compatible with the lower photon statistics. We show that magnetically channeled accretion of plasma onto the surface of the neutron star cannot account for the optical pulsed luminosity (∼ 10 31 erg s −1 ). On the other hand, magnetospheric rotation-powered pulsar emission would require an extremely efficient conversion of spin-down power into pulsed optical and X-ray emission. We then propose that optical Corresponding author: A. Papitto alessandro.papitto@inaf.it pulsar wind meets the accretion disk, within a few light cylinder radii away, ∼ 100 km, from the pulsar.

NuSTAR and Parkes observations of the transitional millisecond pulsar binary XSS J12270–4859 in the rotation-powered state

“…A variety of interpretation have been proposed for the complex behaviour during the LMXB state: an enshrouded pulsar (Coti Zelati et al 2014;Takata et al 2014), a pulsar in a propeller state (Papitto et al 2014;, an intermittent propellering radio pulsar (Ertan 2017) or a low accretion rate pulsar from a trapped disc near corotation (D'Angelo & Spruit 2012) (see also Campana & Di Salvo (2018), for a review). Whether the disc shocks with a striped pulsar wind at a few light cylinder radii away from the pulsar, giving rise synchrotron emission producing the optical and X-ray pulses, is a challenging intepretion put forward by Papitto et al (2019) (see also Veledina et al 2019;Campana et al 2019).…”

The Flare-dominated Accretion Mode of a Radio-bright Candidate Transitional Millisecond Pulsar

“…Interestingly, PSRJ1023+0038 also exhibited optical pulsations during the sub-luminous disk state, which makes it the first millisecond pulsar ever detected in the optical (Ambrosino et al 2017). Papitto et al (2019) argued that the pulsed optical emission originates neither from magnetically channelled accretion nor a rotation-powered pulsar magnetosphere, but synchrotron emission from the intrabinary shock between the pulsar wind and the accretion disk. This would imply that the rotation-powered activity of a pulsar persists in the subluminous disk state.…”

X-ray study of high-and-low luminosity modes and peculiar low-soft-and-hard activity in the transitional pulsar XSS J12270−4859

“…Actually, there is no known mechanisms able to account for the large pulsed optical luminosity in J1023, involving the accretion of matter onto the NS surface (cyclotron emission falls by a factor 35 Ambrosino et al 2017). Papitto et al (2019) proposed that optical and X-ray pulsations are produced in intra-binary shocks when the relativistic wind of the pulsar interacts with the in-flowing matter close to the light cylinder. In the new physical 1 Technically, nsatmos model is for a cooling NS atmosphere, but is has been shown to describe fairly well also low-level accretion.…”

“…Veledina et al (2019) suggested instead that during the low mode, matter is accreted onto the NS. Papitto et al (2019) suggested that flares might come from a complete enshrouding of the pulsar. At variance with the previous scenario, it seems natural here to include flare mode data into the spectral fits, to investigate this possibility.…”

“…In this paper, two possible physical scenario are presented to interpret the puzzling behaviour exhibited during the X-ray active state: one involving a transition between a propeller (see Sect. 2.1) and a radio pulsar Linares 2014) and the other one considering an active radio pulsar all the time (Coti Zelati et al 2014;Takata et al 2014;Papitto et al 2019;Campana et al 2019). Using XMM-Newton observations carried out during both the X-ray active state and radio pulsar state, and selecting low, high (and flare) X-ray emission modes, we test these scenarios on J12270.…”