Swift follow-up observations of the gamma-ray flaring blazar PKS 1454-354
ATel #14712; F. D'Ammando (INAF-IRA Bologna), S. Garrappa (DESY Zeuthen) on behalf of the Fermi Large Area Telescope Collaboration
on 14 Jun 2021; 20:12 UT
Credential Certification: Filippo D'Ammando (dammando@ira.inaf.it)
Subjects: Optical, Ultra-Violet, X-ray, AGN, Black Hole, Blazar, Quasar
Following the gamma-ray activity from the flat spectrum radio quasar PKS 1454-354 observed by Fermi-LAT during 2021 May-June (see ATel #14700), Swift target of opportunity observations were performed between 2021 May 28 and June 12.
Taking into consideration the Swift observations performed during 2008-2021, the source reached on 2021 May 28 and June 12 the highest count rates observed in the 0.3-10 keV energy range (see Swift-XRT Monitoring of Fermi-LAT Sources of Interest). Swift/XRT data were taken in Photon Counting mode for a net exposure of
about 1.0 ksec and 1.2 ksec on 2021 May 28 and June 12, respectively. The X-ray spectrum (0.3-10 keV) observed on 2021 May 28 and June 12 can be fit by an absorbed power-law model with an HI column density consistent with the Galactic value in the direction of the source (n_H = 5.9 x 10^20 cm^-2, Ben Bekhti et al. 2016, A&A, 594, A116) and a photon index of 1.20+/-0.25 and 1.21+/-0.26, respectively. The corresponding observed 0.3-10 keV fluxes are (5.7+/-0.8)e-12 and (4.5+/-0.7)e-12 erg cm^-2 s^-1, respectively. By comparison, the flux estimated in the previous XRT observations ranges between (0.7-2.9)e-12 erg cm^-2 s^-1, indicating a significant increase of X-ray activity in 2021 May-June, in agreement with the observed gamma-ray activity (Fermi Monitored Source List).
Simultaneous Swift/UVOT observations performed on 2021 May 28 and June 12 found PKS 1454-354 brighter in optical and UV bands than previous UVOT observations (see Table below). The brightness is higher on 2021 June 12 than May 28.
Band | 2011-08-10 | 2020-08-22 | 2021-05-28 | 2021-06-12 |
V | 18.94 +/- 0.19 | - | 16.91 +/- 0.12 | 16.64 +/- 0.11 |
B | 19.14 +/- 0.07 | - | 17.39 +/- 0.07 | 17.06 +/- 0.09 |
U | 17.97 +/- 0.05 | - | 16.52 +/- 0.07 | 16.24 +/- 0.08 |
W1 | - | 17.81 +/- 0.06 | 17.38 +/- 0.11 | 16.49 +/- 0.10 |
M2 | - | - | 17.25 +/- 0.13 | 17.22 +/- 0.11 |
W2 | - | - | 17.88 +/- 0.13 | 17.63 +/- 0.12 |
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 M. Marelli (martino.marelli at inaf.it).
We would like to thank the Swift Team, Observatory Duty Scientists, and PI for making these observations possible.