from datetime import datetime


def utc_timestamp(hours_since_first_epoch):
    """Construct a timestamp of the format "%Y-%m-%d %H:%M:%S"
    for the given epoch.

    Arguments:
        hours_since_first_epoch (int):
            Epoch for reftime

    Returns:
        ts (str)
            Timestamp of the format "%Y-%m-%d %H:%M:%S"
    """
    epoch = hours_since_first_epoch * 60 * 60
    ts = datetime.fromtimestamp(epoch).strftime("%Y-%m-%d %H:%M:%S")
    return ts