Volume 555, July 2013
|Number of page(s)||6|
|Published online||12 July 2013|
Two-year monitoring of intra-day variability of quasar 1156+295 at 4.8 GHz ⋆
1 Xinjiang Astronomical Observatory, Chinese Academy of Sciences, 150 Science 1-Street, 830011 Urumqi, PR China
2 Key Laboratory of Radio Astronomy, CAS, 210008 Nanjing, PR China
3 University of Chinese Academy of Sciences, 100049 Beijing, PR China
4 Department of Physics and GXU-NAOC Center for Astrophysics and Space Sciences, Guangxi University, 530004 Nanning, PR China
5 Dipartimento di Fisica e Astronomia, Università di Padova, via Marzolo 8, 35131 Padova, Italy
6 Max-Plank-Institut für Radioastronomie, Auf dem Hügel 69, 53121 Bonn, Germany
Received: 5 December 2012
Accepted: 23 May 2013
Aims. The quasar 1156+295 (4C +29.45) is one of the targets in the Urumqi monitoring program which aimed to search for evidence of annual modulation in the timescales of intra-day variable (IDV) sources.
Methods. The IDV observations of 1156+295 were carried out nearly monthly from October 2007 to October 2009, with the Urumqi 25 m radio telescope at 4.8 GHz.
Results. The source has shown prominent IDV of total flux density in most observing sessions with variability timescales of ≤1 day at 4.8 GHz. The estimated IDV timescales seem to follow an annual cycle that can be fitted with an anisotropic interstellar scintillation model suggesting that a significant part of the flux density variations is due to ISS. The source underwent a dramatic flare in 2008. We studied the possible consequences of the flare on the IDV of 1156+295 by comparing the changes in its IDV characteristics with the evolution of the 43 GHz Very Long Baseline Array core size of the source.
Conclusions. The quasar 1156+295 shows evidence for an annual modulation of its IDV timescales at 4.8 GHz, the ISS-induced IDV timescales and variability strength might be affected by the overall activity state of the source core. More frequent IDV and VLBI measurements are required to confirm the relation between the IDV appearance and the core-size evolution of the source.
Key words: quasars: individual: 4C +29.45 / radio continuum: galaxies / galaxies: jets / ISM: structure / scattering
Table 3, which contains all flux measurements, is only available at the CDS via anonymous ftp to cdsarc.u-strasbg.fr (188.8.131.52) or via http://cdsarc.u-strasbg.fr/viz-bin/qcat?J/A+A/555/A134
© ESO, 2013
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