Fermi Gamma-ray Space Telescope

Fermi ToO 060626-1-1

A ToO observation to observe S3 0218+357 at RA, Dec = 35.2728, 35.9372 (J2000) was approved at 2014-07-16 18:41:12 UTC.

The justification for the ToO is: S3 0218+357 is a gravitationally lensed FSRQ with LAT measured delay of 11.46+/-0.16 days (1 sigma) while it was flaring in 2012. New flaring activity was detected from Jul 13-14 but characterized by an unusually hard spectrum (index = 1.3-1.4; >100 MeV fluxes 6-7 E-7 ph/cm2/s), that strongly deviates from the past flares when its spectrum did not deviate from its quiescent one (index=2.3 typical of a FSRQ). This is an unusually hard spectrum for any flaring LAT source and particularly unusual for a FSRQ to \"turn blue\" (index <2). The requested Fermi ToO covering the 2-sigma interval of the expected delayed emission from the brightest 1.25 day sub-interval of the flare (July 24.7-26.5) with the same spectrum will definitively confirm S3 0218+357 as an unusual \"red turned blue blazar\".

The planned duration is 156.00 ks.

The autonomous request threshold during this ToO is LOW.

The ToO observation should begin between 2014-07-16 00:00:00 UTC and 2014-07-23 18:00:00 UTC.

The ToO observation was requested by DR. SARA BUSON.