Swift follow-up observations of the AGN PKS 0521-36
ATel #15029; F. D'Ammando (INAF-IRA Bologna) and I. Mereu (INFN Perugia)
on 11 Nov 2021; 21:54 UT
Credential Certification: Filippo D'Ammando (dammando@ira.inaf.it)
Subjects: Optical, Ultra-Violet, X-ray, Request for Observations, AGN, Black Hole, Blazar
Referred to by ATel #: 15041
Following the high gamma-ray activity of the AGN PKS 0521-36 detected by Fermi-LAT on 2021 November 8 (see Fermi-LAT Monitored Source List Light Curves ), we performed a Swift target of opportunity observation on November 10.
Swift/XRT data were taken in Photon Counting mode for a total exposure of 1.9 ksec. 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 = 3.58 x10^20 cm^-2, Kalberla et al. 2005, A&A, 440, 775) and a photon index of 1.47+/-0.09. The corresponding 2-10 keV flux is (2.01+/-0.13) x10^-11 erg cm^-2 s^-1, comparable to the highest fluxes observed in 2010 June-July at the time of a previous gamma-ray flaring activity (see D'Ammando et al. 2015, MNRAS, 450, 3975).
Simultaneous Swift/UVOT observations were performed on 2021 November 10. The measured magnitudes are B = 15.59 +/- 0.05, U = 15.02 +/- 0.06, W1 = 15.23 +/- 0.04, and W2 = 15.48 +/- 0.09. As a comparison, UVOT observed magnitudes during 2008-2011 ranges between B = 16.05-15.12, U = 15.63-14.49, W1 = 15.81-14.54, and W2 = 15.97-14.54, suggesting a moderate increase of activity on 2021 November 10 also in optical and UV bands.
In consideration of the ongoing activity of this source, confirmed also by the Swift observations, we strongly encourage further multi-wavelength observations. Further Swift observations of the source are planned on 2021 November 12 and 14.
We would like to thank the Swift Team, the Swift ODS, and the PI for making these observations possible.
