The Spectrum of the Recycled PSR J0437–4715 and Its White Dwarf Companion

Abstract

We present extensive spectral and photometric observations of the recycled pulsar/white-dwarf binary containing PSR J0437−4715, which we analyzed together with archival X-ray and gammaray data, to obtain the complete mid-infrared to gamma-ray spectrum. We first fit each part of the spectrum separately, and then the whole multi-wavelength spectrum. We find that the opticalinfrared part of the spectrum is well fit by a cool white dwarf atmosphere model with pure hydrogen composition. The model atmosphere (T eff = 3950 ± 150 K, log g = 6.98 ± 0.15, R WD = (1.9 ± 0.2) × 10 9 cm) fits our spectral data remarkably well for the known mass and distance (M = 0.25 ± 0.02M ⊙ , d = 156.3 ± 1.3 pc), yielding the white dwarf age (τ WD = 6.0 ± 0.5 Gyr). In the UV, we find a spectral shape consistent with thermal emission from the bulk of the neutron star surface, with surface temperature between 1.25 × 10 5 and 3.5 × 10 5 K. The temprature of the thermal spectrum suggests that some heating mechanism operates throughout the life of the neutron star. The temperature distribution on the neutron star surface is non-uniform. In the X-rays, we confirm the presence of a high-energy tail which is consistent with a continuation of the cut-off power-law component (Γ = 1.56 ± 0.01, E cut = 1.1 ± 0.2 GeV) that is seen in gamma-rays and perhaps even extends to the near-UV. Subject headings: pulsars: individual (PSR J0437−4715); white dwarfs 7

White Dwarf Stars

“…showing clear rapid orbital decay consistent with general relativity prediction due to gravitational wave radiation. White dwarfs have been identified as companions to millisecond pulsars [64][65][66][67][68][69][70][71][72][73][74][75][76] . Ref.…”

Gaiaphotometry for white dwarfs

“…This opacity significantly changes the predicted flux in the B passband at very cool temperatures (T eff 6000 K). Models with this opacity source have been successful in reproducing SEDs of many cool WDs (Kowalski & Saumon 2006;Kilic et al 2009aKilic et al ,b, 2010bDurant et al 2012). The colours for these improved models are accessible from Pierre Bergeron's webpage 4 .…”

Neutron star radius measurement from the ultraviolet and soft X-ray thermal emission of PSR J0437−4715

“…Because of its proximity, J0437 is also the only MSP for which the ∼ 10 5 K thermal emission from the entire pulsar surface is detectable in the soft X-ray range below ∼ 0.4 keV. This third (cool) thermal component is clearly seen in the UV (Kargaltsev et al 2004;Durant et al 2012), but it was poorly constrained in studies that only considered the X-ray data, due to uncertain contributions of a non-thermal component (Bogdanov 2013). This is because the mild excess below ∼ 0.4 keV in the XMM data could be compensated by a soft power-law.…”

“…In addition, it is in a 5.74 day binary orbit with a helium-core white dwarf companion (Bailyn 1993), allowing for a precise radio-timing measurement of the pulsar mass, M NS = 1.44 ± 0.07 M (Reardon et al 2016). The white dwarf has an effective temperature of 3950 ± 150 K (Durant et al 2012), making it very unlikely to contribute significantly to the UV emission of the system. The spin period of J0437, P = 5.76 ms, and its spin-down rate, P = 5.73×10 −20 s s −1 , imply a large spin-down age (after kinematic corrections), τ = P/2 P = 6.7 Gyr, and a weak dipole magnetic field, B = 2.8×10 8 G.…”