Need help passing a variable to the Store function request

I previously simplified the posts request below to a shorter and cleaner code in my opinion which is also show below.

        $post = new Posts;
        $post->title = $request->input('title');
        $post->body = $request->input('body');
        $post->user_id = auth()->user()->id;
        $post->save();

       auth()->user()->publish(
            new Posts(request(['title', 'body', 'user_id']))
        );

I added the ability to upload file images and the cover_img table needs to be equal to a variable but I don't know how to include it in the 'simplified' code request. I tried to add a comma and put 'cover_img' but that didn't seem to work very well.

        $post = new Posts;
        $post->title = $request->input('title');
        $post->body = $request->input('body');
        $post->user_id = auth()->user()->id;
        $post->cover_img = $fileNameToStore;  // new variable added
        $post->save();

       auth()->user()->publish(
            new Posts(request(['title', 'body', 'user_id'])) // not sure how to add $fileNameToStore to this request... any thoughts?
        );