  Single-exposure spectra in large spectral surveys are valuable for time
domain studies such as stellar variability, but there is no available method to
eliminate cosmic rays for single-exposure, multi-fiber spectral images. In this
paper, we describe a new method to detect and remove cosmic rays in multi-fiber
spectroscopic single exposures. Through the use of two-dimensional profile
fitting and a noise model that considers the position-dependent errors, we
successfully detect as many as 80% of the cosmic rays and correct the cosmic
ray polluted pixels to an average accuracy of 97.8%. Multiple tests and
comparisons with both simulated data and real LAMOST data show that the method
works properly in detection rate, false detection rate, and validity of cosmic
ray correction.
