def merger_mass_loss(q, a_1, a_2):
    """Compute mass lost during a GW merger between two BHs. Expression from
    Tichy & Marronetti 2008.

    Parameters
    ----------
    q : `float/array`
        Mass ratio of binary
    a_1 : `float/array`
        Spin of primary BH
    a_2 : `float/array`
        Spin of secondary BH

    Returns
    -------
    loss : `float/array`
        Fraction of total binary mass lost during merger
    """
    v = q / (1 + q)**2
    loss = 0.2 * v + 0.208 * v**2 * (a_1 + a_2)
    return loss