Kavli Affiliate: Roger W. Romani
| First 5 Authors: Roger W. Romani, D. Kandel, Alexei V. Filippenko, Thomas G. Brink, WeiKang Zheng
| Summary:
We describe Keck-telescope spectrophotometry and imaging of the companion of
the “black widow" pulsar PSR~J0952$-$0607, the fastest known spinning neutron
star (NS) in the disk of the Milky Way. The companion is very faint at minimum
brightness, presenting observational challenges, but we have measured
multicolor light curves and obtained radial velocities over the illuminated
“day" half of the orbit. The model fits indicate system inclination $i=59.8pm
1.9^circ$ and a pulsar mass $M_{NS} = 2.35pm 0.17 M_odot$, the largest
well-measured mass found to date. Modeling uncertainties are small, since the
heating is not extreme; the companion lies well within its Roche lobe and a
simple direct-heating model provides the best fit. If the NS started at a
typical pulsar birth mass, nearly $1 M_odot$ has been accreted; this may be
connected with the especially low intrinsic dipole surface field, estimated at
$6times 10^7$G. Joined with reanalysis of other black widow and redback
pulsars, we find that the minimum value for the maximum NS mass is $M_{rm max}
> 2.19 M_odot$$(2.09 M_odot)$ at $1sigma$$(3sigma)$ confidence. This is
$sim 0.15 M_odot$ heavier than the lower limit on $M_{rm max}$ implied by
the white-dwarf–pulsar binaries measured via radio Shapiro-delay techniques.
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