PHP working with timestamps to determine week

I am building a PHP calendar that has a week view and also a primary month view. I have a database which stores all events for everyday, and loads everything at start for the month.

The month view is complete and works fine, let me show you how it works:

Query to withdraw all events in that month:

WHERE a.target_date BETWEEN $month_start AND $month_end

    $source_date = mktime(0,0,0,$month,1,$year);
    $days_in_month = date("t",$source_date);
    $month_start = mktime(0,0,0,$month,1,$year);
    $month_end = mktime(23,59,0,$month,$days_in_month,$year);

Note that $month and $year are determined in the URL, so that isn't a problem

My problem, I wish to use the same logic to withdraw all my events in the current week. However I am not certain how I can do this.

I am able to find the week number we are in the month with this code:

$current_date = time();
$current_date = date("Y-m-d",$current_date);
$week = get_weeks($current_date, "monday");