My deceased father was the inventor of the patent number US3601948 A. I want to know who is the rightful owner of this patent since he has past?
My condolences. If your father did not assign (sell) his rights to the patent then it is his personal property and like anything else he owned becomes part of his estate. Ownership of the patent rights passes to his heirs (or devisees if he had a will) according the laws of your state, like all his other personal property.
If he assigned the patent before it was issued this is usually but not always shown on the patent itself. You can look up whether he ever assigned the patent at http://assignments.uspto.gov/assignments/q?db=pat. A patent is generally good for, has a term of 20 years from the earliest date of filing. If you or yours have become the new owners be aware that patents need to have fees paid at intervals to keep them valid, roughly at years 3, 7 and 11 years from the date of issuance, otherwise the patent will expire early (terminate the patent rights early).