Optical, X, Gamma-ray activity of the FSRQ PKS 1313-333

ATel #8483; Luigi Pacciani
on 31 Dec 2015; 14:39 UT
Credential Certification: Luigi Pacciani (luigi.pacciani@iaps.inaf.it)

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We asked a Swift ToO campaign on the FSRQ PKS 1313-333 (z=1.21), triggered by prolonged High Energy activity detected with FERMI-LAT. The trigger method detected activity at E > 20GeV/(1+z) with TS ~79 from 2015-12-10 to 2015-12-30, following the prescription of Pacciani et al. 2014, ApJ, 790, 45.

FERMI-LAT detected Two Gamma-ray photons of about 50 GeV within the last week.

The flux integrated on the whole period is (7.9+-1.7)E^-9 ph cm^-2 s^-1 (E> 3 GeV), to be compared to a catalog flux of (0.47+-0.07)E^-9 ph cm^-2s^-1 (E> 3 GeV).

The Swift Follow-up revealed the source in high state in optical/UV and X-ray.

The preliminary Swift-UVOT photometry on 2015-12-27 is (in AB photometric system):

v: 15.86+-0.03

b: 16.20+-0.02

u: 16.60+-0.02

w1: 17.33+-0.02

m2: 17.51+-0.03

w2: 17.85+-0.02

Magnitudes have not been corrected for Galactic extinction.

These photometric data correspond to the brightest obtained with Swift-uvot observations.

On 2015/12/29 the source showed a flux about 20% fainter in optical/UV.

For comparison, on 2005/09/07, the UVOT measured magnitudes were:

v: 18.59+-0.18

b: 19.60+-0.27

u: 19.87+-0.13

w1: 20.62+-0.12

m2: 20.87+-0.11

w2: 21.07+-0.09

The simultaneous Swift-XRT observation on 2015/12/27 gives a photon index 1.44+-0.21 (90% c.l.), an unabsorbed flux of (2.5+-0.3)E-12 erg/cm2/s which is the brightest detected with swift-XRT.

We encourage further multi-wavelength observations. We thank the Swift team and Swift Observatory Duty Scientist for rapidly scheduling our observations.