It's very difficult to see exactly what you are trying to duplicate from your sample image but I think I have exactly what it is that you need. In this snapshot, the bottom image is your original and the image above is the vector re-create.
I have included a download link for the adobe illustrator file saved as version CS6.
Re-Created Gradient Line With Gradient Drop Shadow
- Paste your original image into a new illustrator document and name that layer, in your layers panel, as the original image and toggle the lock icon
- Create a new layer and in that new layer, grab your rectangle tool and draw a thin rectangle directly over the original image which you are using as your template
- Grab your selection tool and click on that new rectangle and while holding the shift key, drag that new rectangle upward so it will not block the original image.
- While that new rectangle is still selected, opened your gradients panel and click on linear gradient. You should then see the gradient slider. Double click on the Black slider on the right and adjust it's color as needed and adjust the slider itself until the gradient visually looks the same as the original.
Now to create the drop shadow, we will use the offset path command.
- Create a new layer below that layer where you created your thin rectangle and name it offset path.
- Using your selection tool, select that new gradient rectangle you've previously created and go to edit menu/copy
- Go back to your layers panel and select the offset path layer you created and go back to edit menu/paste in place.
- Now with that new pasted object in your offset path layer in your layers panel, make sure that object is selected and go to menu item object/path/offset path. This will create a larger rectangle on all sides so you will have to grab your selection tool after you apply the offset path and adjust the left and right sides so they match the left and right sides of your thin rectangle.
- Adjust the gradient colors and the gradient slider locations to your desired values (as we did earlier)
- Once that gradient looks correct, go to menu item edit/copy then back to menu item edit/paste in back.
- Using your down arrow key, nudge that item down a few times and once again go to your gradients panel and adjust the gradient colors and the slider locations to your desired results. Now repeat this entire process in this step one more time