Optical, X, HE gamma-ray activity of the FSRQ PKS 0035-252

ATel #11874; L. Pacciani (INAF-Italy), F. Ambrosino (INAF-Italy)
on 20 Jul 2018; 10:02 UT
Credential Certification: Luigi Pacciani (luigi.pacciani@iaps.inaf.it)

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On 12th Luly 2018 the FSRQ PKS 0035-252 (z=0.498), triggered our HE monitor of FERMI-LAT data at E > 10 GeV with TS ~49 (see, Pacciani et al. 2014, ApJ, 790, 45 for a description of the method), showing a power-law gamma-ray spectrum exceeding 40 GeV in the satellite frame (see also the ATel #11854 by the Fermi-LAT collaboration on 14th July 2018). We obtained 3 follow-up observations with Swift starting on 13th July 2018. The source showed the brightest optical and X-ray flux ever detected with The Neil Gehrels Swift Observatory, With a peak flux reached on the last pointing on 18th July 2018. On 16th July 2018, the source was observed twice within 6 hours and showed a variability of 25% with all optical/nuv filters (2 nearby sources where used as reference). On 18th July 2018 the source was observed for a reduced time, and with the W2 only filter. The magnitude (Vega system) was: 14.30+-0.02 (stat error only) and The x-ray flux was (5.+-1)*10^-12 erg cm^-2 s^-1 (0.3-10 KeV).

On 16th July 2018, the photometry (Vega sytem) was:

VV: 14.85 +- 0.03

UU: 14.61 +- 0.03

W1: 14.51 +- 0.02

M2: 14.46 +- 0.02

W2: 14.59 +- 0.02

(stat error only).

The simultaneous Swift-XRT observation gives a counting rate of cps. The X-ray spectrum was fitted with an absorbed power-law, with unabsorbed flux: (5.4+-+-0.4)10^-12 erg cm^-2 s^-1, and photon index: 1.30+-0.26 (0.3-10keV).

We would like to thank the Swift team and Swift Observatory Duty Scientist for rapidly scheduling our observations.