Swift follow-up of the flaring blazar PKS 0736+01

ATel #12790; F. D'Ammando (INAF-IRA Bologna) on behalf of the Fermi Large Area Telescope Collaboration
on 21 May 2019; 19:49 UT
Credential Certification: Filippo D'Ammando (dammando@ira.inaf.it)

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Following the flaring activity of the flat spectrum radio quasar PKS 0736+01 at redshift z = 0.18941 (Ho & Kim 2009, ApJS, 184, 398) observed in gamma rays by Fermi-LAT (LAT GCN 1, LAT GCN 2) and by AGILE-GRID (ATel #12733), a Swift target of opportunity observation was performed on May 20.

Swift-XRT data were taken in Photon Counting mode for a net exposure of about 2.0 ksec. The X-ray spectrum (0.3-10 keV) observed in 2019 May 20 can be fit by an absorbed power law model with a HI column density consistent with the Galactic value in the direction of the source (n_H = 7.8 x 10^20 cm^-2, Kalberla et al. 2005, A&A, 440, 775) and a photon index of 1.39 +/- 0.16. The corresponding observed 0.3-10 keV flux is (10.1+/-0.9) x10^-12 erg cm^-2 s^-1. The flux observed on 2019 May 20 is slightly higher than the value observed on 2014 November 21 during a previous gamma-ray flaring activity (ATel #6742), with a similar photon index.

Simultaneous Swift-UVOT observations were performed on 2019 May 20. The measured magnitudes are B = 15.91 +/- 0.06, U = 15.24 +/- 0.06, W1 = 15.41 +/- 0.08, W2 = 15.65 +/- 0.10, comparable to the values observed during the 2014 November flare (ATel #6742). This confirms the high activity state of the source in optical and UV. Flaring activity from PKS 0736+01 was recently observed also in near-infrared (ATel #12782).

In consideration of the ongoing activity of this source, confirmed also by the Swift observations, we encourage further multiwavelength observations. For this source the Fermi LAT contact person is F. D'Ammando (dammando@ira.inaf.it).

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