Simultaneous Multicolor Observations of Starlink's Darksat by The Murikabushi Telescope with $MITSuME$

We present the $g^{\mathrm{\prime }}$-, $R_{\mathrm{c}}$-, and $I_{\mathrm{c}}$-band magnitudes and associated colors of the Starlink’s STARLINK-1113 (one of the standard Starlink satellites) and 1130 (Darksat) with a darkening treatment to its surface. By the 105 cm Murikabushi telescope/$MITSuME$, simultaneous multicolor observations for the above satellites were conducted four times: on April 10, 2020, May 18, 2020 (for Darksat), and June 11, 2020 (for Darksat and STARLINK-1113). We found that (1) $g^{\mathrm{\prime }}$-band apparent magnitudes of Darksat ($6.95\pm 0.11-7.65\pm 0.11$ mag) are comparable to or brighter than that of STARLINK-1113 ($7.69\pm 0.16$ mag), (2) the shorter the observed wavelength is, the fainter the satellite magnitudes tend to become, (3) the reflected flux by STARLINK-1113 is extremely ($>1.0$ mag) redder than that of Darksat, (4) there is no clear correlation between the solar phase angle and orbital-altitude-scaled magnitude, (5) by flux-model fitting of the satellite trails with the blackbody radiation, it is found that the albedo of Darksat is about a half of that of STARLINK-1113. Especially, the result (1) is inconsistent with the previous studies. However, considering both solar and observer phase angles and atmospheric extinction, the brightness of STARLINK-1113 can be drastically reduced in the $g^{\mathrm{\prime }}$ and $R_{\mathrm{c}}$ band. Simultaneous multicolor-multispot observations more than three colors would give us more detailed information regarding the impact by the low Earth orbit satellite constellations.