Fermi LAT detection of a potential echo gamma-ray flare from gravitational lens S3 0218+35
ATel #4371; M. Giroletti (INAF-IRA Bologna), M. Orienti (Univ. Bologna, INAF-IRA Bologna), C. C. Cheung (NRC/NRL); on behalf of the Fermi Large Area Telescope Collaboration
on 11 Sep 2012; 20:42 UT
Credential Certification: Teddy Cheung (ccheung@milkyway.gsfc.nasa.gov)
Subjects: Gamma Ray, >GeV, AGN, Blazar
The Large Area Telescope (LAT), on board the Fermi Gamma-ray Space Telescope, recently observed (ATel #4343, ATel #4361) a re-brightening of the gravitationally lensed blazar S3 0218+35, reaching a peak daily flux (E > 100 MeV) of (2.4+/-0.3) x10^-6 ph cm^-2 s^-1 on September 6, about ten days after a previous gamma-ray peak. Since the time delay between the variations in the two compact radio source images of S3 0218+35 is 10.5+/-0.4 days (Biggs et al. 1999, MNRAS, 304, 349), the renewed activity could represent the gravitational lens time-delayed counterpart of the previous event.
Preliminary follow-up analysis indicates that the re-brightening of the source has now ceased, with daily fluxes (E > 100 MeV) below 1.0x10^-6 ph cm^-2 s^-1 on September 7 and 8. Based on the comparable durations and the time interval between the flares, this could be the first clear detection of a gamma-ray gravitational lens echo.
Because Fermi operates in an all-sky scanning mode, regular gamma-ray monitoring of this source will continue. In consideration of the peculiar state of this source (see also ATel #4351) we encourage multiwavelength observations. For this source the Fermi LAT contact person is Teddy 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.
