Swift observation of strong X-ray and UV activity of CTA 102

ATel #9841; S. Ciprini (ASDC Rome & INFN Perugia, Italy), F. Verrecchia (ASDC Rome & INAF OAR Rome, Italy)
on 9 Dec 2016; 20:43 UT
Credential Certification: Stefano Ciprini (stefano.ciprini@asdc.asi.it)

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The flat spectrum radio quasar CTA 102 (also historically known as 4C +11.69, PKS 2230+11, OY 150, DA 582, H 2230+114 and a well known gamma-ray source in the MeV/GeV bands, 3EG J2232+1147, 3FGL J2232.5+1143) has been subject into a prolonged outburst activity at optical and gamma-ray energy bands since the end of Oct. 2016 (see, for example, preliminary optical results in ATel#9676, ATel#9732, ATel#9756, ATel#9776, ATel#9801, ATel#9808, ATel#9821, preliminary gamma-ray results by AGILE in ATel#9743, ATel#9788, ATel#9840, and by the public Fermi LAT uncalibrated flux data). This MeV-peaked gamma-ray blazar (detected by OSSE, McNaron-Brown et al. 1995, ApJ, 451, 575, COMPTEL, Blom et al. 1995, A&A, 295, 330, Zhang et al. 2005, A&A, 444, 767, and EGRET, Nolan et al. 1993, ApJ, 414, 82 on board of the CGRO, by AGILE, ATel#8476, and by the Fermi LAT, Acero et al. 2015, ApJS, 218, 23) has redshift z=1.037 (Schmidt 1965, ApJ, 141, 1295).

Following this prolonged optical/gamma-ray activity a target of opportunity program to the Swift Gamma Ray Burst Explorer satellite has been proposed by us and performed starting from Nov. 14 2016. Initially we requested Swift XRT data in Photon Counting (PC) mode for a total exposure of about 18 ksec divided in six observations to monitor the evolution of the source. Each of the six single X-ray spectrum (0.3-10 keV) can be fit by an absorbed single power-law model, keeping fixed the Galactic HI column density value in the direction of the source (n_H = 5.05 X 10^20 cm^-2, Kalberla et al. 2005, A&A, 440, 775). The preliminary corresponding unabsorbed (0.3-10 keV) integral daily flux increased from (19.8+/-0.7)X 10^-12 erg cm^-2 s^-1 detected by XRT on Nov. 16, 2016 to (31.8 +/-0.8)X 10^-12 erg cm^-2 s^-1 detected by XRT on Nov. 23, 2016, the latter corresponding to about a factor 2 times higher than the highest flux detected by XRT in the same energy band during the Sep. 25 - Oct 5, 2012 and Nov. 10-20, 2012 (Casadio et al. 2015, ApJ, 813, 51) X-ray flares. The corresponding power law photon spectral indexes are respectively 1.24+/-0.07 and 1.21+/-0.08.

The de-reddened Swift UVOT flux density values, obtained using the official calibration (Breeveld et al.2011) and a galactic value E(B-V)=0.061 in the direction of the source (Schlafly et al.2011) from Nov. 14 to Nov. 23 for the 3 optical filters are in the following ranges: V=[23.41+/-0.68 - 7.27+/-0.21] mJy; B=[17.89+/-0.46 - 5.35+/-0.14] mJy; U=[14.03+/-0.46 - 4.12+/-0.14] mJy; and for the 3 UV filters are in the following ranges: W1=[8.26+/-0.27 - 2.34+/-0.08] mJy; M2=[7.63+/-0.30 - 1.92+/-0.08] mJy; W2=[5.92+/-0.20 - 1.53+/-0.05] mJy. These are a factor 1 to about 3 times higher than those reported during the optical-UV flare of the end of Sep. 2012.

This result represents an increase in the flux both at X-ray and UV bands, correlated with the large outburst observed at optical bands and the current long-term phase of high-flux activity pointed out at GeV gamma-ray band by AGILE.

In consideration of the ongoing activity at optical, X-ray and gamma-ray bands of CTA 102 (4C +11.69, PKS 2230+11) we encourage multiwavelength observations. The Swift gamma-ray burst explorer mission is part of NASA's medium explorer (MIDEX) program, led by NASA with participation of Italy and the UK. We would like to thank the Swift Team for making these observations possible, in particular S. Sbarufatti as the Swift Observatory Duty Scientist.