We studied the multiwavelength properties of NGC 3521, the Milky Way galaxy-twin, from UV- to radio, exploring the data from GALEX for UV-, SDSS for optical, 2MASS, WISE, MIPS (Spitzer) and PACS, SPIRE (Herschel) for IR-, and NRAO VLA for radio ranges. To obtain the spectral energy distribution (SED), we exploited the CIGALE software and constructed SEDs without (model A) and with (model B) AGN module. The type of nuclear activity of isolated galaxy NGC 3521 is confirmed as the LINER.

       We also present the results of the photometric data processing. Exploring the ZTF observations in 2018–2024, we found, for the first time, a weak photometric variability of the nuclear activity, where the correlation between g-r color indices and g-magnitude for long-term timescale shows a BWB trend (bluer-when-brighter) with a Pearson coefficient r(g–r)=0.56, which is a medium correlation. To detect the variability of NGC 3521 during the day (IDV), we provided observations using a Zeiss-600 telescope with an aperture size of 8″ at the Terskol observatory. The data obtained in the R-filter with an exposure of 90 sec for three hours on Feb 11, 2022, serve in favor of a trend towards an increase in brightness with the amplitude of variability of 0.04 ± 0.001 mag.