M. Giroletti (INAF-IRA Bologna), M. Orienti (Univ. Bologna, INAF-IRA Bologna), C. C. Cheung (NRL/NRL) on behalf of the Fermi Large Area Telescope Collaboration
ATel #4361; M. Giroletti (INAF-IRA Bologna), M. Orienti (Univ. Bologna, INAF-IRA Bologna), C. C. Cheung (NRL/NRL) on behalf of the Fermi Large Area Telescope Collaboration
on 8 Sep 2012; 09:10 UT
Credential Certification: Marcello Giroletti (giroletti@ira.inaf.it)
Subjects: Gamma Ray, >GeV, Request for Observations, AGN, Blazar
The Large Area Telescope (LAT), on board the Fermi Gamma-ray Space Telescope, has observed an increasing gamma-ray flux from a source positionally consistent with the blazar S3 0218+35 (also known as 2FGL J0221.0+3555, Nolan et al. 2012, ApJS, 199, 31) with radio coordinates R.A.: 35.27279 deg, Dec: +35.93715 deg (J2000, Patnaik et al. 1992, MNRAS, 254, 655).
S3 0218+35 is a gravitationally lensed blazar (Patnaik et al. 1993, MNRAS, 261, 435), with a time delay between the variations in the two compact radio source images of 10.5+/-0.4 days (Biggs et al. 1999, MNRAS, 304, 349). The gamma-ray source was previously found in a high state on 2012 August 26 (ATel #4343), with an average daily gamma-ray flux (E>100 MeV) of (1.6+/-0.3) x 10^-6 photons cm^-2 s^-1.
Preliminary analysis indicates that the source re-brightened in gamma-rays starting September 3, with daily fluxes (E > 100 MeV) above 1.0x10^-6 ph cm^-2 s^-1, reaching (2.4+/-0.3) x10^-6 ph cm^-2 s^-1 on September 6th (MJD 56176, errors are statistical only). Since the flare reported in ATel #4343 started on Aug. 25 and peaked on Aug. 27, the present enhanced gamma-ray activity possibly represents the gravitational lens time delayed counterpart of the previous event. This would be the first clear detection of a gravitational lens echo in gamma rays.
Because Fermi operates in an all-sky scanning mode, regular gamma-ray monitoring of this source will continue. In consideration of the ongoing activity of this source we encourage multiwavelength observations. For this source the Fermi LAT contact person is C. C. Cheung (ccheung@milkyway.gsfc.nasa.gov).
The Fermi LAT is a pair conversion telescope designed to cover the energy band from 20 MeV to greater than 300 GeV. It is the product of an international collaboration between NASA and DOE in the U.S. and many scientific institutions across France, Italy, Japan and Sweden.