Fermi LAT detection of renewed GeV gamma-ray activity from blazar AO 0235+164

ATel #7975; Stefano Ciprini (ASDC Rome & INFN Perugia, Italy), on behalf of the Fermi Large Area Telescope Collaboration.
on 1 Sep 2015; 15:34 UT
Credential Certification: Stefano Ciprini (stefano.ciprini@asdc.asi.it)

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The Large Area Telescope (LAT), one of two instruments on the Fermi Gamma-ray Space Telescope, has observed flaring gamma-ray emission from a source positionally consistent with the blazar AO 0235+164 (also known as OD 160, PKS 0235+164, 1ES 0235+164 and 3FGL J0238.6+1636), with radio coordinates (J2000) R.A.: 39.662209 deg, Dec.: 16.616465 deg (Johnston et al. 1995, AJ, 110, 880). This blazar has a redshift z=0.94 (Cohen et al. 1987, ApJ, 318, 577).

Preliminary analysis indicates that on 29, 30 and 31 August 2015 AO 0235+164 was in a high-flux state, with a daily gamma-ray flux (E>100MeV) respectively of (1.2+/-0.2) X 10^-6 photons cm^-2 s^-1, (1.2+/-0.2) X 10^-6 photons cm^-2 s^-1, and (0.8+/-0.2) X 10^-6 photons cm^-2 s^-1 (statistical uncertainty only). The corresponding daily spectral photon indices (E>100MeV) of respectively 2.0+/-0.1, 2.05+/-0.05 and 2.0+/-0.2 are consistent with the average index of 2.057+/-0.024 reported in the 3FGL catalog.

A peak 6-hour integrated gamma-ray flux of (1.5+/-0.5) X 10^-6 photons cm^-2 s^-1 (statistical uncertainty only), is reached on September the 1st 2015, 00:00-06:00 UT, corresponding to about 10 times greater than the average flux reported in the third Fermi-LAT source catalog, 3FGL (Acero et al. 2015, ApJS 218, 23).

This is the third time that the LAT collaboration is announcing gamma-ray flaring activity from AO 0235+164 through an ATel, after those in September and October 2008 (ATel#1744 and ATel#1784) and after the 2008-2009 flaring state (Ackermann et al. 2012, ApJ, 751, 159).

AO 0235+164 is one of the "LAT Monitored Sources" and consequently a preliminary estimation of the daily gamma-ray flux observed by Fermi LAT is publicly available (http://fermi.gsfc.nasa.gov/ssc/data/access/lat/msl_lc/source/0235p164).

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 persons are L. C. Reyes (e-mail: lreyes04@calpoly.edu) and S. Raino' (silvia.raino@ba.infn.it).

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.