Fermi LAT and Swift flare of the FSRQ 4C +40.25

ATel #8339; Bryce Carpenter (CUA/NASA/GSFC), Roopesh Ojha (NASA/GSFC/UMBC), and Giovanna Pivato (INFN/University of Pisa) on behalf of the Fermi Large Area Telescope Collaboration.
on 26 Nov 2015; 16:18 UT
Credential Certification: Roopesh Ojha (Roopesh.Ojha@gmail.com)

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The Large Area Telescope (LAT) on board the Fermi Gamma-ray Space Telescope has observed a gamma-ray flare from a source positionally consistent with the flat spectrum radio quasar (FSRQ) 4C +40.25 (also known as B2 1020+40 and 3FGL J1023.1+3952, Acero et al. 2015, ApJS 218, 23) with coordinates RA: 10h 23m 11.5661s, Dec: 39d 48m 15.378s, J2000, (Helmboldt et al. 2007, ApJ, 658, 203) and a redshift of 1.254 (Xu et al. 1994, AJ, 108, 395).

Preliminary analysis indicates that from 20 November 2015 this source has been in a high-flux state and, on 24 November 2015, it has risen to a daily averaged gamma-ray flux (E>100MeV) of (1.0+/-0.2) X 10^-6 photons cm^-2 s^-1 (statistical uncertainty only) corresponding to a flux increase of a factor of about 65 with respect to its four-year average flux in the 3FGL. The corresponding photon spectral index of 2.1+/-0.1 is in the typical range for a 3FGL blazar.

Since 4C+40.25 lies about 5 arcminutes from the radio/optical candidate-quasar FBQS J102333.5+395312, Swift ToO observations were made on 24 November 2015 to determine which of these two objects was flaring in gamma rays. Swift/XRT data were taken in Photon Counting mode for a total exposure of about 2.0 ksec. The X-ray spectrum (0.5-10 keV) of 4C +40.25 can be fit by an absorbed power-law model with an HI column density set to the Galactic value of 1.27X10^20 cm^-2 (Kalberla et al. 2005, A&A, 440, 775) using the abundances of Wilms et al. (2000, ApJ, 542, 914) and the cross sections of Verner et al. (1996, ApJ, 465, 487). The observed flux is (3.7^{+1.0}_{-0.8})X10^-12 erg cm^-2 s^-1 with a photon index of 1.24 +/- 0.24. This is about 3.7 times brighter than an archival XRT observation from 3 October 2012. No such brightening was observed for J102333.5+395312.

Simultaneous Swift/UVOT observations were made using the UVM2 filter, which showed that 4C+40.25 has brightened from 17.25+/-0.15 to 16.75+/-0.16 i.e. by 0.5 magnitudes. J102333.5+395312 has also brightened, but only from 17.19+/-0.15 to 16.88+/-0.17.

Because Fermi operates in an all-sky scanning mode, regular gamma-ray monitoring of this source will continue. We encourage further multifrequency observations of this source. For this source the Fermi-LAT contact person is Bryce Carpenter (carpb01@gmail.com).

We would like to thank the Swift Team for making these observations possible, in particular K. L. Page as the Swift Observatory Duty Scientist.

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.