Swift follow-up of the flaring FSRQ PKS 1127-14

ATel #15385; Filippo D'Ammando (INAF-IRA Bologna)
on 19 May 2022; 11:28 UT
Credential Certification: Filippo D'Ammando (dammando@ira.inaf.it)

Tweet

Following the flaring activity of the flat spectrum radio quasar PKS 1127-14 at redshift z = 1.184 (Wilkes 1986, MNRAS, 218, 331) detected in gamma rays by Fermi-LAT on 2022 May 12 (ATel #15379), Swift target of opportunity observations were performed on 2022 May 17 and 18.

Swift-XRT data were taken in Photon Counting mode for a net exposure of about 1.2 ksec and 0.9 ksec, respectively. Taking into consideration the Swift observations performed during 2007-2022, the source reached on 2022 May the highest count rate observed in the 0.3-10 keV energy range so far (see Swift-XRT Monitoring of Fermi-LAT Sources of Interest; Stroh & Falcone, 2013, ApJS, 207, 28 ).

The X-ray spectrum (0.3-10 keV) observed on 2022 May 17 and 18 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 = 3.5 x 10^20 cm^-2, Ben Bekhti N. et al., 2016, A&A, 594, A116) and a photon index of 1.06 +/- 0.16 and 1.05 +/- 0.22, respectively. The corresponding (observed) 0.3-10 keV flux is (1.47 +/- 0.16) x10^-11 erg cm^-2 s^-1 and (1.38 +/- 0.18) x10^-11 erg cm^-2 s^-1. These fluxes are approximately 50 per cent higher than the previous peak value observed by Swift-XRT on 2020 December 13, i.e. (9.5+/-1.2) x10^-12 erg cm^-2 s^-1, with a photon index of 1.26 +/- 0.19 (ATel #14265, ATel #14280).

Simultaneous Swift-UVOT observations were performed on 2022 May 17 and 18. The measured magnitudes in optical and UV bands show an intermediate brightness between the values observed on 2020 December 13 and 2007 March 24 (see table below).

The measured magnitudes are:

Band	2022 May 17	2022 May 18	2020 Dec 13	2007 Mar 24
V	16.59 +/- 0.10	-	16.87 +/- 0.14	16.44 +/- 0.04
B	16.95 +/- 0.08	-	17.05 +/- 0.09	16.68 +/- 0.04
U	15.88 +/- 0.07	-	15.99 +/- 0.08	15.61 +/- 0.05
W1	15.72 +/- 0.08	-	15.88 +/- 0.08	15.45 +/- 0.05
M2	15.96 +/- 0.08	-	15.91 +/- 0.07	15.56 +/- 0.06
W2	16.06 +/- 0.07	16.06 +/- 0.06	16.19 +/- 0.08	15.80 +/- 0.05

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 M. H. Siegel as the Swift Observatory Duty Scientist.