EMB ERJ 135 ER/LR
Flight Crew Instrument; Flight Crew Flight Instructor; Flight Crew Multiengine; Flight Crew Air Transport Pilot (ATP)
Flight Crew Last 90 Days 100; Flight Crew Total 2650; Flight Crew Type 1800
Situational Awareness
Conflict NMAC
Flight Crew Took Evasive Action
Human Factors
Response to an RA in the vicinity of Sussex (FWN) and West Milford (4N1) airports around the SAX VOR. We were at 4000 ft on vectors for the Runway 19 approach into TEB.  ATC cleared us to descend to 3000 ft.  In the descent we got a TA for traffic at our 10 o'clock 200 ft. below us. We arrested the descent at about 3600 ft. ATC also issued us a traffic alert for the same target. We queried ATC about the traffic.  We then got a descend RA command to which we responded. We observed a low wing single engine aircraft fly over our Captain side Direct View window at approximately 100 ft [lateral distance].  We alerted ATC to the RA response he said he was not talking to the traffic. We then proceeded to TEB without further incident.
EMB-135 First Officer reported an NMAC in the vicinity of FWN and 4N1 airports on arrival to TEB.