The high redshift ( z = 0.997 ) blazar B2 1308+326 was observed contemporaneously at x-ray , optical and radio wavelengths in June 1996 .
The x-ray observations were performed with ASCA .
The ASCA results were found to be consistent with reanalysed data from two earlier ROSAT observations .
The combined ASCA and ROSAT data reveal an x-ray spectrum that is best fit by a broken power law with absorber model with photon spectral indices of \Gamma _ { soft } = 3.4 _ { -1.1 } ^ { +5.1 } and \Gamma _ { hard } = 1.63 _ { -0.09 } ^ { +0.10 } and a break energy at 1.1 _ { -0.4 } ^ { +0.4 } keV in the rest-frame of the blazar .
The break in the x-ray spectrum is interpreted , from the shape of the simultaneous broadband spectral energy distribution , to be the emerging importance of inverse Compton ( IC ) emission which dominates the ASCA spectrum.The faint optical state reported for these observations ( m _ { V } = 18.3 \pm 0.25 ) is incompatible with the high synchrotron flux previously detected by ROSAT .
The IC emission detected by both ROSAT and ASCA was not significantly affected by the large change in the synchrotron component .

Mg ii emission was detected with an equivalent width ( W _ { \lambda } ) of \sim 15Å , significantly different from previously reported values .
The small and variable W _ { \lambda } in B2 1308+326 may be due to the highly variable continuum and not intrinsically weak lines in the source .
A lower limit on the Doppler boost factor calculated from the contemporaneous data is consistent with expectations for highly polarised quasars and higher than expected for BL Lacs .
Absorption at a level of N _ { \mathrm { H } } = 3.0 _ { -0.6 } ^ { +2.3 } \times 10 ^ { 20 } cm ^ { -2 } was detected which is in excess of the Galactic value of N _ { \mathrm { H } } = 1.1 \times 10 ^ { 20 } cm ^ { -2 } , indicating the possible presence of a foreground absorber .
A gravitational microlensing scenario can not therefore be ruled out for this blazar .
No significant variability on timescales of hours was detected in the optical or x-ray data .

B2 1308+326 could be a typical radio-selected BL Lac in terms of peak synchrotron frequency and optical and radio variability but its high bolometric luminosity , variable line emission and high Doppler boost factor make it appear more like a quasar than a BL Lac .
It is suggested that B2 1308+326 be considered as the prototype of this class of composite source .