We report the detection of eclipses in LSPM J1112+7626 , which we find to be a moderately bright ( I _ { C } = 12.14 \pm 0.05 ) very low-mass binary system with an orbital period of 41.03236 \pm 0.00002 days , and component masses M _ { 1 } = 0.395 \pm 0.002 { M } _ { \odot } and M _ { 2 } = 0.275 \pm 0.001 { M } _ { \odot } in an eccentric ( e = 0.239 \pm 0.002 ) orbit .
A 65 day out of eclipse modulation of approximately 2 \% peak-to-peak amplitude is seen in I -band , which is probably due to rotational modulation of photospheric spots on one of the binary components .
This paper presents the discovery and characterization of the object , including radial velocities sufficient to determine both component masses to better than 1 \% precision , and a photometric solution .
We find that the sum of the component radii , which is much better-determined than the individual radii , is inflated by 3.8 ^ { +0.9 } _ { -0.5 } \% compared to the theoretical model predictions , depending on the age and metallicity assumed .
These results demonstrate that the difficulties in reproducing observed M-dwarf eclipsing binary radii with theoretical models are not confined to systems with very short orbital periods .
This object promises to be a fruitful testing ground for the hypothesized link between inflated radii in M-dwarfs and activity .