The SDSS-V Black Hole Mapper Reverberation Mapping Project: CIV BAL Acceleration in the Quasar SBS 1408+544

TL;DR

This study tracks a highly variable CIV broad absorption line in quasar SBS 1408+544 over eight years, revealing a systematic velocity increase that provides insights into quasar outflow dynamics.

Contribution

It presents the first long-term measurement of BAL acceleration in a quasar, demonstrating systematic velocity shifts over years using SDSS data.

Findings

Measured a velocity shift of -683 km/s over 8 years

Detected an average acceleration of 1.04 cm/s^2

Observed non-constant acceleration on shorter timescales

Abstract

We present the results of an investigation of a highly variable CIV broad absorption-line feature in the quasar SBS 1408+544 (z=2.337) that shows a significant shift in velocity over time. This source was observed as a part of the Sloan Digital Sky Survey Reverberation Mapping Project and the SDSS-V Black Hole Mapper Reverberation Mapping Project, and has been included in two previous studies, both of which identified significant variability in a high-velocity CIV broad absorption line (BAL) on timescales of just a few days in the quasar rest frame. Using ~130 spectra acquired over eight years of spectroscopic monitoring with SDSS, we have determined that this BAL is not only varying in strength, but is also systematically shifting to higher velocities. Using cross-correlation methods, we measure the velocity shifts (and corresponding acceleration) of the BAL on a wide range of timescales, measuring an overall velocity shift of delta v = -683 (+89, -84) km s-1 over the 8-year monitoring period. This corresponds to an average rest-frame acceleration of a=1.04 (+0.14, -0.13) cm s-2, though the magnitude of the acceleration on shorter timescales is not constant throughout. We place our measurements in the context of BAL-acceleration models and examine various possible causes of the observed velocity shift.