Swift follow-up of the on-going flare of the blazar B2 1420+32

ATel #13417; Vandad Fallah Ramazani (FINCA, University of Turku), Giacomo Bonnoli (University of Siena and INFN Pisa), Filippo D'Ammando (INAF-IRA Bologna), Matteo Cerruti (Institut de Ciencies del Cosmos - Universitat de Barcelona), Chiara Righi (INAF-OA Brera), Julian Sitarek (Department of Astrophysics, The University of Lodz)
on 22 Jan 2020; 17:02 UT
Credential Certification: Giacomo Bonnoli (giacomo.bonnoli@unisi.it)

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Following the recent activity in high-energy gamma-rays (ATel #13382) and the detection of very-high-energy gamma-ray emission from B2 1420+32 with the MAGIC telescopes (ATel #13412), Swift target of opportunity observations were performed on 2020 January 22.

The X-ray Telescope on-board the Neil Gehrels Swift Observatory has taken data in Photon Counting mode for a net exposure of about 1.5 ks. The X-ray spectrum (0.3-10 keV) 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 = 1.1 x 10^20 cm^-2; Ben Bekhti N. et al., 2016, A&A, 594, A116) and a photon index of 1.92 +/- 0.09. The corresponding observed 0.3-10 keV flux is (5.8+/-0.5) x10^-12 erg cm^-2 s^-1. As a comparison, the fluxes observed by XRT on 2020 January 2 and 19 are (4.4+/- 0.5) x10^-12 erg cm^-2 s^-1 and (5.6+/ 0.5) x10^-12 erg cm^-2 s^-1, respectively, with a photon index of 1.30 +/- 0.11 and 1.91 +/- 0.10. These observations indicate an increasing trend of the flux and a softening of the spectrum observed on January 19 and 22 with respect to the observation performed on January 2. This behavior is in agreement with the extension of the jet synchrotron emission in the X-ray band.

From the analysis of Swift/UVOT observations performed in 2020 January 19 and 22 we measured magnitudes (Vega System) W1 = 12.65 +/- 0.05 and W2 = 13.52 +/- 0.03, respectively.

As a comparison the observed magnitudes on 2020 January 2 are W1 = 14.23 +/- 0.06 and W2 = 14.28 +/- 0.06. This indicates a significant increase of the UV activity in the last days.

In consideration of the ongoing activity of this source, confirmed also by the Swift observations, we encourage further multi-wavelength observations.

We would like to thank the Swift Team for making these observations possible, in particular Brad Cenko as Swift PI, and the Swift Observatory Duty Scientists.