In this paper we report on \sim 10 years of observations of PSR J2051 - 0827 , at radio frequencies in the range 110–4032 MHz .
We investigate the eclipse phenomena of this black widow pulsar using model fits of increased dispersion and scattering of the pulsed radio emission as it traverses the eclipse medium .
These model fits reveal variability in dispersion features on timescales as short as the orbital period , and previously unknown trends on timescales of months–years .
No clear patterns are found between the low-frequency eclipse widths , orbital period variations and trends in the intra-binary material density .
Using polarisation calibrated observations we present the first available limits on the strength of magnetic fields within the eclipse region of this system ; the average line of sight field is constrained to be 10 ^ { -4 } G \lesssim B _ { || } \lesssim 10 ^ { 2 } G , while for the case of a field directed near-perpendicular to the line of sight we find B _ { \perp } \lesssim 0.3 G. Depolarisation of the linearly polarised pulses during the eclipse is detected and attributed to rapid rotation measure fluctuations of \sigma _ { \text { RM } } \gtrsim 100 rad m ^ { -2 } along , or across , the line of sights averaged over during a sub-integration .
The results are considered in the context of eclipse mechanisms , and we find scattering and/or cyclotron absorption provide the most promising explanation , while dispersion smearing is conclusively ruled out .
Finally , we estimate the mass loss rate from the companion to be \dot { M } _ { \text { C } } \sim 10 ^ { -12 } M _ { \odot } yr ^ { -1 } , suggesting that the companion will not be fully evaporated on any reasonable timescale .