Tidally locked planetary-mass companion to PSR J1311-3430

Flares in extreme black widow PSR J1311-3430

Quote :

PSR J1311-3430 is one of the most extreme examples of the 'black widow' pulsar class. Here a sub-stellar companion, tidally locked to the millisecond pulsar, orbits in 1.5hours. The pulsar heats the facing side of the companion to ~10,000 K. Since its discovery, J1311 has been observed to exhibit flares at X-ray and optical wavelengths. The peak energy flux during these flares is higher than the intercepted pulsar spindown power, implying an energy storage mechanism. We report on a set of simultaneous optical and X-ray observations with LCO (g'), XMM Newton (EPIC and OM u'), and NICER, designed to probe the flare SED and its emission mechanism.
We find that the X-ray flare spectra are well-fit by a power law model, but this power law can not be connected to the optical u' and g' band fluxes. This suggests that the flares have two separate emission components. The spectral index between the u' and g' band is close to zero, albeit with large uncertainties. Based on the limited information from these two optical bands, we suggest that the flares consist of a blackbody component with temperatures of ~13,000-25,000K, and a power law component in the X-ray. The power law is estimated to be the more energetic of the two, implying that it traces the accelerated particles, which heat a dense medium to produce a secondary thermal component. In this way, they may be analogous to solar flares, where reconnection in the companion magnetosphere generates non-thermal elections, which then heat the companion photosphere, creating thermal blackbody emission. Our planned observations had more broad-band optical coverage; with only g and u' band fluxes, we are unable to fully constrain this component. Simultaneous multi-band optical observations (eg. ug'riz) will be needed to check our interpretation of the soft component, while hard X-ray observations above 10 keV could constrain the full extent of the power law emission.

The mass of the secondary is below 15 M_Jup. But the presence of such an extreme substellar companion is known since long time. To say:

A Spectroscopic Study of the Extreme Black Widow PSR J1311-3430

Quote :

We report on a series of spectroscopic observations of PSR J1311-3430, an extreme black-widow gamma-ray pulsar with a helium-star companion. In a previous study we estimated the neutron star mass as M_NS= 2.68+/-0.14M_Sun (statistical error), based on limited spectroscopy and a basic (direct heating) light curve model; however, much larger model-dependent systematics dominate the mass uncertainty. Our new spectroscopy reveals a range of complex source behavior. The variable He I companion wind emission lines can dominate broad-band photometry, especially in red filters or near minimum brightness, and the wind flux should complete companion evaporation in a spin-down time. The heated companion face also undergoes dramatic flares, reaching 40,000K over 20% of the star; this is likely powered by a magnetic field generated in the companion. The companion center-of-light radial velocity is now well measured with K_CoL = 615.4+/-this http URL. We detect non-sinusoidal velocity components due to the heated face flux distribution. Using our spectra to excise flares and wind lines, we generate substantially improved light curves for companion continuum fitting. We show that the inferred inclination and neutron star mass, however, remain sensitive to the poorly constrained heating pattern. The neutron star's mass, M_NS, is likely less than the direct heating value and could range as low as 1.8M_Sun for extreme equatorial heating concentration. While we cannot yet pin down M_NS, our data imply that an intrabinary shock reprocesses the pulsar emission and heats the companion. Improved spectra and, especially, models that include such shock heating are needed for precise parameter measurement.

Or:

PSR J1311-3430: A Heavyweight Neutron Star with a Flyweight Helium Companion

Quote :

We have obtained initial spectroscopic observations and additional photometry of the newly discovered Pb=94min gamma-ray black-widow pulsar PSR J1311-3430. The Keck spectra show a He-dominated, nearly H-free photosphere and a large radial-velocity amplitude of 609.5+/-7.5km/s. Simultaneous seven-color GROND photometry further probes the heating of this companion, and shows the presence of a flaring infrared excess. We have modeled the quiescent light curve, constraining the orbital inclination and masses. Simple heated light-curve fits give M_NS=2.7Msun, but show systematic light-curve differences. Adding extra components allows a larger mass range to be fit, but all viable solutions have M_NS>2.1Msun. If confirmed, such a large M_NS substantially constrains the equation of state of matter at supernuclear densities.

Wherein:

Quote :

The γ-ray pulsar ephemeris gives an orbit of a_NS sin i = 0.010581 lt-s for a minimum companion mass of ∼ 8 ×10^-3 M_⊙.

That is about 8 M_Jup, likely greater but well within planetary/substellar domain.

There is also a Wikipedia entry for PSR J1311-3430 with a nice NASA animation too.