Swift follow-up of the blazar OJ 49

ATel #13339; F. D'Ammando (INAF-IRA Bologna)
on 9 Dec 2019; 14:01 UT
Credential Certification: Filippo D'Ammando (dammando@ira.inaf.it)

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Following the recent high optical state of the BL Lac OJ 49 (ATel #13322), Swift target of opportunity observations were performed on December 5 and 9.

Swift/XRT data were taken in Photon Counting mode for a net exposure of about 2.0 and 0.8 ksec. The X-ray spectrum (0.3-10 keV) observed in 2019 December 5 and 9 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 = 2.3 x 10^20 cm^-2; Ben Bekhti N. et al., 2016, A&A, 594, A116) and a photon index of 1.63 +/- 0.17 and 2.26 +/- 0.25, respectively. The corresponding unobserved 0.3-10 keV fluxes are (4.5+/-0.3) x10^-12 erg cm^-2 s^-1 and (5.8+/-0.5) x10^-12 erg cm^-2 s^-1, showing an increasing trend of the flux, in comparison also with the value observed on 2019 February 2, (4.2+/-0.4) x10^-12 erg cm^-2 s^-1, with a photon index of 1.45 +/- 0.18. Taking into consideration the Swift/XRT observations performed during 2009-2019, the source reached on 2019 December 9 the second highest count rate in the 0.3-10 keV energy range (see OJ 49).

Simultaneous Swift/UVOT observations in 2019 December 9 found OJ 49 about 1.7 mag brighter in U-band with respect to the observations performed on 2019 February 2 (U = 16.02+/-0.05), and about 0.4 mag brighter in all bands compared to the UVOT observations performed on 2019 December 5. The measured magnitudes (Vega System) are:

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 K. L. Page, as the Swift Observatory Duty Scientist.