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Swift follow-up of the gamma-ray flaring blazar PKS 0727-11

ATEL # 2901; F. D'Ammando (INAF-IASF Palermo), K. V. Sokolovsky (MPIfR/ASC Lebedev) on behalf of the Fermi Large Area Telescope Collaboration
on 3 Oct 2010; 6:14 UT
Distributed as an Instant Email Notice (Request for Observations)
Password Certification: Filippo D'Ammando (filippo.dammando@iasf-roma.inaf.it)

Subjects: Optical, Ultra-Violet, X-ray, Gamma Ray, Request for Observations, AGN, Quasars

Following the gamma-ray flare of the high redshift flat spectrum radio quasar PKS 0727-11 (also known as PKS J0730-1141 and 1FGL J0730.3-1141, Abdo et al. 2010, ApJS, 188, 405; z = 1.59, Zensus et al. 2002) detected by Fermi LAT on September 21, 2010 (ATel #2860), we performed two Swift target of opportunity observations on September 26 and 29.

Swift/XRT data were taken in Photon Counting mode for a total exposure of about 9.0 ksec. Adding the two observations, the X-ray spectrum (0.3-10 keV) 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 = 3.46 x 10^21 cm^-2, Kalberla et al. 2005) and a photon index of 1.72+/-0.23. The corresponding unabsorbed 0.3-10 keV flux is (1.4+/-0.3) x10^-12 erg cm^-2 s^-1. This flux is significantly lower than that previously observed by Swift/XRT on 2008 December 6, (2.7+/-0.5) x10^-12 erg cm^-2 s^-1, and 2007 May 8-9, (2.2+/-0.5) x10^-12 erg cm^-2 s^-1, with a photon index of 1.72+/-0.20 and 1.44+/-0.25, respectively.

Swift/UVOT has detected the source at U = 20.1+/-0.2 on September 29, 2010. Previously, the source has been observed by Swift/UVOT in this band on February 18, 2007 (U = 19.2+/-0.3), May 2, 2007 (U>20), and December 4, 2008 (U = 18.02+/-0.03). A comparison of the UVOT images at two epochs can be found here: http://scan.sai.msu.ru/~kirx/ATel/PKS0727-11_UVOT_U_2008-2010.png

After the flare occurred on September 21, the gamma-ray activity of PKS 0727-11 continued in the following days (see Fermi LAT public light curve http://fermi.gsfc.nasa.gov/FTP/glast/data/lat/catalogs/asp/current/lightcurves/PKS0727-11_86400.png ). Moreover, a NIR flare on September 30 was reported by Carrasco et al. (ATel #2895).

The low activity level currently observed in optical and X-rays by Swift with respect to past observations suggests that the ongoing flaring mechanism does not influence the optical-to-X-ray part of the spectrum of the source.

Further multiwavelength observations are encouraged. For this source the Fermi LAT contact person is A. Tramacere (e-mail:andrea.tramacere@unige.ch).

We would like to thank the Swift Team for making these observations possible, in particular the duty scientists as well as the science planners.


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R. E. Rutledge , Editor
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