Systematic Search for X-ray Counterparts of Fermi-LAT 4FGL Unassociated Sources Using Swift Observations: New Blazars, Pulsars, and more

MOTIVATED BY THE RELEASE OF THE FL8Y SOURCE POSITIONS (PRELIMINARY 4FGL CATALOG) AND THE CONTINUED NEED TO IDENTIFY MANY UNASSOCIATED FERMI SOURCES WE PROPOSE TO USE SWIFT TO CONTINUE THE PREVIOUSLY SUCCESSFUL GI PROGRAM TO SEARCH FOR X-RAY AND UV/OPTICAL COUNTERPARTS OF UNASSOCIATED FERMI GAMMA-RAY SOURCES WHICH ARE LIKELY TO BE DOMINATED BY NEW GAMMA-RAY BLAZARS AND WHICH MAY ALSO HARBOR NEW EXCITING SOURCE CLASSES. PREVIOUS PROGRAMS LED TO SWIFT OBSERVATIONS OF 261 AND 199 FERMI-LAT UNASSOCIATED SOURCES FROM THE 1FGL AND 2FGL CATALOGS RESPECTIVELY AS WELL AS 522 OBSERVATIONS OF 3FGL UNASSOCIATED SOURCES. POSSIBLE X-RAY COUNTERPARTS ARE FOUND IN ~1/3 OF THESE OBSERVATIONS. THIS PROPOSED PROGRAM WOULD CONTINUE THIS EFFORT BY: (1) ADDING>200 SWIFT OBSERVATIONS/YEAR OF THE EXCITING UNASSOCIATED SOURCES FROM THE FERMI 4FGL CATALOG AND (2) PLACING ANALYZED DATA PRODUCTS ON A PUBLIC WEB PAGE WITHIN HOURS OF THE OBSERVATIONS. THIS ANALYSIS WILL DETERMINE THE BASIC PROPERTIES OF ALL DETECTED XRAY SOURCES WITHIN THE FERMI-LAT LOCALIZATION REGIONS. IN PARTICULAR SWIFT-XRT WILL OBTAIN ACCURATE SOURCE POSITIONS (