ASCA observation of the lensed blazar PKS 1830-211: An implication of X-ray microlensing

We present ASCA observations of the gravitationally lensed blazar PKS 1830-211. Intensity variations of about 10% and spectral variations were detected in the eight observations made at intervals of about 5 days. The spectral variations can be described by a change of absorption column density if we represent the spectrum with a single power-law model. However, it is more likely that the spectrum consists of two spectral components with different absorptions and that their intensity ratio varies. The column densities of the two components are consistent with the column densities of the two lensed images. However, the intensity ratio is different by a factor of 7.4 from the magnification ratio of the two lensed images. We suggest that the discrepancy is most likely due to X-ray microlensing, among several other possibilities. We estimate that the size of the X-ray emission region must be smaller than ∼3 × 10¹⁴ cm in order to explain the observed microlensing magnification.