Dark supernova remnant buried in the Galactic Center "Brick" G0.253+0.016 revealed by an expanding CO-line bubble

We performed a (CO)-C-12- and (CO)-C-13-line study of the "Brick" (G0.253+0.016) in the Galactic Center (GC) by analyzing archival data obtained with the Nobeyama 45 m telescope. We present kinematics and molecular gas distributions in the longitude-velocity diagram, and suggest that the Brick is located along the GC Arm I in the central molecular zone (CMZ), which yields a distance from the Sun of 8 kpc and a Galactocentric distance of 0.2 kpc. The major- and minor-axis diameters of the Brick are D-x x D-y= 8.4 x 4.1 pc at position angles of 40 and 130 degrees, respectively, and the scale radius is r(Bri =) root D-x x D-y = 2.96, pc. The molecular mass inferred from the (CO)-C-12-line integrated intensity is M-Bri ; X-CO similar to 5.1 x 10(4) M-circle dot for a conversion factor X-CO;GC = 1.0 X 10(20) H-2 cm (-2) [K km s(-1)](-1). On the other hand, the dynamical (virial) mass for the measured velocity dispersion of sigma(v)=10.0, km s(-1) is calculated to be M (Bri;vir) similar to 6.8 X 10(4)M(circle dot), which yields a new conversion factor of X (CO;Bri) =1.3 X 10(20) H-2 cm(-2)[K km s-(1)](-1). The Brick's center has a cavity surrounded by a spherical molecular bubble of radius r (bub) =1.85 pc and mass similar to 1.7 X 10(4) M-circle dot expanding at v(exp) similar or equal to 10 km s(-1) with a kinetic energy of E-0 similar to 1.7 X 10(49)erg. If the bubble is approximated by an adiabatic spherical shock wave, the age is estimated to be t similar to 2/5 r(bub)/v(exp)similar to 7.2 X 10(4) yr. Neither non-thermal radio structures nor thermal radio emission indicative of the H ii region are found in the archival data from MeerKAT. We suggest that the molecular bubble is a dark supernova remnant buried in the Brick, which has therefore experienced past (similar to 0.1 Myr ago) massive star formation with a supernova explosion.