We present upper limits on the X-ray emission for three neutron stars .
For PSR J1840 - 1419 , with a characteristic age of 16.5 Myr , we calculate a blackbody temperature upper limit ( at 99 % confidence ) of kT _ { \mathrm { bb } } ^ { \infty } < 24 ^ { +17 } _ { -10 } eV , making this one of the coolest neutron stars known .
PSRs J1814 - 1744 and J1847 - 0130 are both high magnetic field pulsars , with inferred surface dipole magnetic field strengths of 5.5 \times 10 ^ { 13 } and 9.4 \times 10 ^ { 13 } G , respectively .
Our temperature upper limits for these stars are kT _ { \mathrm { bb } } ^ { \infty } < 123 ^ { +20 } _ { -33 } eV and kT _ { \mathrm { bb } } ^ { \infty } < 115 ^ { +16 } _ { -33 } eV , showing that these high magnetic field pulsars are not significantly hotter than those with lower magnetic fields .
Finally , we put these limits into context by summarizing all temperature measurements and limits for rotation-driven neutron stars .