Swift detection of increased X-ray activity from gamma-ray flaring blazar PKS 1424-41

ATel #4770; Stefano Ciprini (ASI ASDC & INAF OAR Rome), Sara Cutini (ASI ASDC & INAF OAR Rome) on behalf of the Fermi Large Area Telescope Collaboration
on 30 Jan 2013; 17:25 UT
Credential Certification: Stefano Ciprini (stefano.ciprini@asdc.asi.it)

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Following enduring gamma-ray flaring activity of the flat spectrum radio quasar PKS 1424-41 (also known as 2FGL J1428.0-4206, Nolan et al. 2012, ApJS, 199, 31) detected by Fermi LAT during January 2013, two Swift target of opportunity observations were performed on January 24 and 27, 2013. Recent gamma-ray and X-ray flaring activity from the source was observed on January 6 and January 7 (ATel#4714 and ATel #4717). Gamma-ray flaring activity was observed in the period January 13 - 27 when Fermi LAT detected daily-averaged gamma-ray fluxes (E>100MeV) ranging from about 2.0x 10^-6 to 2.6x 10^-6 photons cm^-2 s^-1. PKS 1424-41 is one of the "LAT Monitored Sources", and consequently, a preliminary, uncalibrated estimation of the daily gamma-ray flux observed by Fermi LAT is publicly available at: http://fermi.gsfc.nasa.gov/ssc/data/access/lat/msl_lc/source/PKS_1424-41.

Swift XRT data were taken in Photon Counting mode in two pointings of total exposure of about 2 ksec each. Preliminary analysis indicates that the X-ray spectrum (0.3-10 keV) of PKS 1424-41 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 = 7.7 x 10^20 cm^-2, Kalberla et al. 2005, A&A, 440, 775) and a photon index of 1.4+/-0.2 and 1.5+/-0.2 for the observation performed on January 24 and January 27, respectively. The corresponding observed 0.3-10 keV fluxes are (6.5+/-0.3) x10^-12 erg cm^-2 s^-1 and (6.2+/-0.3) x10^-12 erg cm^-2 s^-1 respectively, higher than the flux observed by Swift XRT on January 7 that was (5.5+/- 0.4)x10^-12 erg cm^-2 s^-1. Swift UVOT observed PKS 1424-41 in UV bands on January 24 and 27 detecting U band (350.1 nm) filter magnitudes of 15.03+/-0.01 and 14.98+/-0.01 respectively, and W1 band (263.9 nm) filter magnitude of 15.57+/-0.01 on January 27.

Further multiwavelength observations are encouraged. For this source the Fermi LAT contact person is F. Longo (francesco.longo@ts.infn.it).

We would like to thank the Swift Team for making these observations possible, in particular B. Sbarufatti and D. Malesani as Swift Observatory Duty Scientists.