The Large Sky Area Multi-object Fiber Spectroscopic Telescope (LAMOST) Quasar Survey: The Fourth and Fifth Data Releases

We present the Data Release 4&5 quasarcatalog from the quasarsurvey by Large Sky Area Multi-Object Fiber Spectroscopic Telescope ( LAMOST), which includes quasarsobserved between September 2015 and June 2017. There are a total of 19,253 quasarsidentified by visual inspections of the spectra. Among them, 11,458 are independently discovered by LAMOST, in which 3296 were reported by SDSS DR12 and DR14 quasarcatalog after our survey began, while the rest 8162 are new discoveries of LAMOST. We provide the emission line measurements for the Halpha, Hbeta, MgII and/or CIV for 18100 quasars. Since LAMOSTdoes not have absolute flux calibration information, we obtain the monochromatic continuum luminosities by fitting the SDSS photometric data using the quasarspectra, and then estimate the black hole masses. The catalog and spectra for these quasarsare available online. This is the third installment in the series of LAMOST quasarsurvey which has released spectra for totally ~43,000 quasarshitherto. There are 24,772 independently discovered quasars, 17,128 of which are newly discovered. In addition to the great supplement to the new quasardiscoveries, LAMOSThas also provided a large database (overlapped with SDSS) for investigating the quasarspectral variability and discovering unusual quasars, including changing-look quasars, with ongoing and upcoming large surveys.