Fermi LAT detection of a GeV flare from the gravitationally lensed blazar S3 0218+35

ATel #4343; S. Ciprini (ASI ASDC & INAF OAR, Rome), on behalf of the Fermi Large Area Telescope Collaboration
on 28 Aug 2012; 20:45 UT
Credential Certification: Stefano Ciprini (stefano.ciprini@asdc.asi.it)

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The Large Area Telescope (LAT), one of the two instruments on the Fermi Gamma-ray Space Telescope, has observed gamma-ray flaring activity 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, and B2 0218+35, OD 330, lens B0218+357) placed at 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; Browne et al. 1993, MNRAS, 263, 32; Lehar et al. 2000, ApJ, 536, 584; Cohen et al. 2003, ApJ, 583, 67) with source redshift z=0.944+/-0.002 (Cohen et al. 2003, ApJ, 583, 67) while the intervening and lensing spiral galaxy has redshift z = 0.6846 (Zeiger et al. 2010, ApJ, 709, 386). S3 0218+35 is a small separation optical lens (335 mas separation, Biggs et al. 1999, MNRAS, 304, 349) possessing one of the smallest Einstein rings in the radio band (0''.33 diameter, Heidt et al. 2004, A&A, 418, 813; Cohen et al. 2003, ApJ, 583, 67; Oguri 2007, ApJ, 660, 1) and it represents an important object for studies of gravitational lensing, Hubble constant value and individual molecular clouds at high redshifts (Jethava et al. 2007, A&A, 472, 435; Zeiger et al. 2010, ApJ, 709, 386). The time delay between the variations in the two compact radio source images is 10.5+/-0.4 days (Biggs et al. 1999, MNRAS, 304, 349).

Preliminary analysis indicates that on 2012 August 26, S3 0218+35 was in a high state with an average daily gamma-ray flux (E>100MeV) of (1.6 +/- 0.3) x 10^-6 photons cm^-2 s^-1 (errors are statistical only), about 16 times greater than the average flux reported in the second Fermi LAT catalog (2FGL). A bright daily flux level around 1 x 10^-6 photons cm^-2 s^-1 was already detected on 2012 August 22 and 25 as well.

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. 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.