Swift follow-up of the flaring blazar PKS 0903-57

ATel #15058; I. Mereu (INFN Perugia) and F. D'Ammando (INAF-IRA Bologna)
on 23 Nov 2021; 11:35 UT
Credential Certification: Filippo D'Ammando (dammando@ira.inaf.it)

Tweet

Following the flaring gamma-ray activity of the blazar PKS 0903-57 (ATel #15057), we performed Swift target of opportunity observations on 2021 November 12, 15, and 18.

Swift/XRT data were taken in Photon Counting mode for a total exposure of 2.4 ksec, 2.4 ksec, and 2.6 ksec on 2021 November 12, 15, and 18, respectively. Taking into consideration the Swift/XRT observations performed during 2018-2021, the source reached on 2021 November 18 one of the highest count rate observed so far in the 0.3-10 keV energy (see Swift-XRT Monitoring of Fermi-LAT Sources of Interest ). 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 = 2.6x10^21 cm^-2, Ben Bekhti et al., 2016, A&A, 594, A116) and a photon index of 1.17 +/- 0.18, 1.52 +/- 0.18, and 1.59 +/- 0.15 on 2021 November 12, 15, and 18, respectively. The corresponding observed 0.3-10 keV fluxes are (7.3 +/- 0.7)e-12, (5.5 +/- 0.6)e-12, and (8.1 +/- 0.7)e-12 erg cm^-2 s^-1, respectively. As a comparison, the X-ray spectrum of the source collected on 2021 August 8 and 11 is fitted with an absorbed power-law with a photon index of 1.58 +/- 0.28 and 1.30 +/- 0.25, respectively. The corresponding observed 0.3-10 keV fluxes on 2021 August 8 and 11 are (4.1 +/- 0.7)e-12 and (4.2 +/- 0.5)e-12 erg cm^-2 s^-1, respectively. This confirms the increase of the X-ray activity of PKS 0903-57 during 2021 November.

Simultaneous Swift/UVOT observations were performed. The measured magnitudes are: w1 = 16.12 +/- 0.08 and m2 = 16.89 +/- 0.07 on 2021 November 12; w2 = 16.31 +/- 0.06 on November 15; u = 15.11 +/- 0.05 on November 18. As a comparison, the measured magnitudes observed on 2021 August 8 and 11 are m2 = 17.37 +/- 0.08 and w2 = 17.70 +/- 0.07, respectively, indicating an increase of activity also in UV during 2021 November.

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

We would like to thank the Swift Team, the Swift ODS, and the PI for making these observations possible.