Swift XRT follow-up observations of the SBS 1343+537

ATel #16699; Federica Giacchino (INFN Roma Tor Vergata & SSDC ASI), Fausto Casaburo (INFN Roma Tor Vergata & SSDC ASI), Stefano Ciprini (INFN Roma Tor Vergata & SSDC ASI), on behalf of the Fermi Large Area Telescope Collaboration, Francesco Verrecchia (INAF OAR & SSDC).
on 9 Jul 2024; 20:19 UT
Credential Certification: Federica Giacchino (federica.giacchino@roma2.infn.it)

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Following the flaring activity observed (ATel#16671) from a gamma-ray source positionally consistent with the FR-I radio galaxy SBS 1343+537 also known as RX J1345.7+5332, TXS 1344+537, and 4FGL J1346.5+5330 in the 14-year fourth Fermi-LAT catalog (4FGL) Data Release 4 (4FGL-DR4; Ballet et al. 2024, arXiv:2307.12546), with coordinates R.A. = 206.438980 deg, Dec = +53.547858 deg (J2000; Petrov & Taylor 2011, AJ, 142, 89), we requested a high-urgency Swift target of opportunity multiple observation.

Swift XRT data were taken in photon counting mode for a total net exposure of approximately 1.95 ksec split in two observations performed on June 25, 2024 (two days after the Fermi LAT flare announced in ATel#16671) for a period of 1.5 ksec exposure, and on June 27, 2024 for a period of 0.45 ksec. The XRT X-ray spectrum of SBS 1343+357 obtained on June 25 has been fitted by an absorbed single power law with the HI column density fixed to the Galactic value of N_HI = 10^22 cm^-2 (Dickey & Lockman 1990), and a fixed power-law photon spectral index of 2.09+/-0.27. The X-ray flux in the 0.4-10 keV energy band is 4.4 x 10^-12 erg cm^-2 s^-1. The XRT observation of June 27 has not sufficient statistics.

Simultaneous Swift-UVOT observations have been performed. The observed magnitudes on June 25 are: B=17.81+/-0.06, U=17.00+/-0.06, UVW1=16.95+/-0.07, UVW2=16.70+/-0.05. On June 27 these are: V=16.95+/-0.15 , B=17.83+/-0.13, U=16.87+/-0.11, W1=16.80+/-0.11, M2=16.85+/-0.15, W2=16.79+/-0.09.

We analysed for comparison also some archival UVOT observation, obtaining on September 28, 2019: M2=17.86+/-0.09, and for September 15, 2019: W2=17.78+/-0.08, showing that the source UV flux on 2019 was lower.

In consideration of the ongoing activity of this source, confirmed also by the Swift observations, and radio observations proposed at the SRT, we encourage further multiwavelength observations. For this source, the Fermi-LAT contact persons are F. Casaburo (fausto.casaburo[at]roma2.infn.it), S. Ciprini (stefano.ciprini[at]roma2.infn.it) and F. Giacchino (federica.giacchino[at]roma2.infn.it).

We would like to thank the Swift Team for making these observations possible, in particular J. J. DeLaunay as the Swift Observatory Duty Scientist.