Quasar J1344+3150 Velocity Shift and Continuum Weakening: Evidence of Acceleration in Mg II and Al III Broad Absorption Lines

We obtained the spectra of quasar J1344+3150 from the SDSS data release 16 (DR16; Ahumada et al. 2020), which were archived on MJD 53503 and MJD 56363, respectively. The resolution of these two spectra are R \≈ 2000, respectively. The MJD 53503 spectrum covers a wavelength range from 3800 to 9200 Å, while the MJD 56363 spectrum covers a wavelength range from 3600 to 10 000 Å. The median signal-to-noise ratios of the MJD 53503 and MJD 56363 spectra are 21 and 24, respectively. \nBy iteratively fitting the continuum within the wavelength regions that are relatively free from strong emission lines and absorption lines, we obtained a power-law continuum of each original spectrum (see the top panel of Fig. 1). Then we normalized the two original spectra using their corresponding power-law continuum (see the middle panel of Fig. 1). In the power-law continuum normalized spectra, we detected three broad absorption systems (systems A, B, and C). We measured the EW and full width at half-maximum (FWHM) of these three broad absorption systems in the Al III and Mg II ions, following the methods in our previous studies [e.g. equations (2) and (3) in Lu & Lin (2018)]. The measurements can be seen in Table 1. Note that system B in the Mg II ion in the MJD 56363 spectrum is nearly undetectable. \nWe found that system A exhibited a velocity shift between the two observations in both the Mg II and Al III ions. Following Lu & Lin (2019), we determined the line centre of a BAL by averaging the EWs of the troughs. In order to more correctly estimate the line centres, we generated 10 000 simulated spectra via adding Gaussian noise to the original spectra according to the corresponding flux density errors, and then used the same procedure to measure the line centres for these simulated spectra. Then, we estimated the line centre and the measurement errors according to the median values and the standard deviations of the 10 000 trials, respectively. Finally, we got the centroid radial velocities of the Mg II BAL of system A for the MJD 53503 and 56363 spectra, which are -16 194 ± 39 and -17 295 ± 61 km s-1, respectively. The difference between their velocities is -1101 ± 80 km s-1, which corresponds to an acceleration rate of 1.087 ± 0.079 cm s-2. Meanwhile, the centroid radial velocities of the Al III BAL of system A are -16 184 ± 77 and -17 353 ± 29 km s-1 for the MJD 53503 and 56363 spectra, respectively, and their velocity difference is -1170 ± 69 km s-1, corresponding to an acceleration rate of 1.155 ± 0.068 cm s-2. \nWe integrated the wavelength range from 1600 to 3000 Å to obtain the flux of each continuum, and find out that, during a rest-frame time of about 3.21 yr, the continuum of quasar J1344+3150 experienced an obvious weakening with the fraction variation of about -0.423.