There are many suggestions to this but I think none of them will get you where you want. If you intend to use this flare somewhere else you don't have to convert into a transparent object. All you need to do is copy and paste it in front of the work you intend to apply the effect and make sure that transparency mode is set to screen.
Here's an old solution I found that might work:
Right click on the image and select "Copy image link".
Then in Photoshop, while a document is open, go to File-Place Embedded.
When the dialog box opens place the link in the file name and click on Place.
The image should open as a smart object.
Here's the workspace on a png I just copied:
I know this is an old question, but just in case anyone else needs a relatively simple answer.
Presuming that you have the following:
An image (A)
Another image (B) that consists of the first image (A) overlaid with a third image (C) that you do not have a separate file for
A need to construct a clean copy of image C (perhaps to turn the overlay on and off)