Add a reference

Signed-off-by: Bruno Khélifi <khelifi@in2p3.fr>

VOHE-Note.bib

@@ -175,3 +175,18 @@ @article{gammapy:2023
     volume = 678,
     pages = "A157",
 }
+
+%FF technique
+@article{mattox:1996,
+       author = {{Mattox}, J.~R. and {Bertsch}, D.~L. and {Chiang}, J. and {Dingus}, B.~L. and {Digel}, S.~W. and {Esposito}, J.~A. and {Fierro}, J.~M. and {Hartman}, R.~C. and {Hunter}, S.~D. and {Kanbach}, G. and {Kniffen}, D.~A. and {Lin}, Y.~C. and {Macomb}, D.~J. and {Mayer-Hasselwander}, H.~A. and {Michelson}, P.~F. and {von Montigny}, C. and {Mukherjee}, R. and {Nolan}, P.~L. and {Ramanamurthy}, P.~V. and {Schneid}, E. and {Sreekumar}, P. and {Thompson}, D.~J. and {Willis}, T.~D.},
+        title = "{The Likelihood Analysis of EGRET Data}",
+      journal = {Astrophysical Journal},
+     keywords = {GAMMA RAYS: OBSERVATIONS, METHODS: DATA ANALYSIS, METHODS: STATISTICAL},
+         year = 1996,
+        month = apr,
+       volume = {461},
+        pages = {396},
+          doi = {10.1086/177068},
+       adsurl = {https://ui.adsabs.harvard.edu/abs/1996ApJ...461..396M},
+      adsnote = {Provided by the SAO/NASA Astrophysics Data System}
+}