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Multiband optical monitoring of the blazars S5 0716+714 and BL Lacertae

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 نشر من قبل C. S. Stalin
 تاريخ النشر 2005
  مجال البحث فيزياء
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 تأليف C.S. Stalin




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We report results of multiband optical monitoring of two well known blazars, S5 0716+714 and BL Lacertae, carried out in 1996 and 2000-01 with an aim to study optical variations on time scales from minutes to hours and longer.The light curves were derived relative to comparison stars present on the CCD frames. Night to night flux variations of >0.1 mag were observed in S5 0716+714 during a campaign of ~2 weeks in 1996.A good correlation between the lightcurves in different optical bands was found for both inter-night and intra-night observations. Two prominent events of intra-night optical variability were detected in S5 0716+714.Each of these rapidly varying segments of the lightcurves trace an exponential flux profile whose rate of variation is the same in both cases. Our long-term monitoring data of S5 0716+714 showed a distinct flare around JD 2451875 which can be identified in the BVRI bands.This flare coincides with the brightest phase recorded during 1994-2001 in the long-term lightcurves reported by Raiteri et al.(2003). No evidence for the bluer when brighter trend was noticed on inter-night and intra-night time scales. On the other hand, our nearly simultaneous multiband observations of BL Lacertae in October 2001 showed flux variations that were not achromatic. This blazar was found to become bluer when brighter on intra-night time scales and there is a hint of the same trend on inter-night time scales. Based on five nights of observations during a week, BL Lacertae showed a peak night-to-night variability of ~0.6 mag in B. Thus, we found that the present observations of the two blazars, reveal a contrasting behaviour in terms of the dependence of spectral hardening with increasing brightness, at least on intra-night, and possibly also on inter-night, time scales.



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53 - E. Pian 2004
We have performed observations of the blazar S5 0716+714 with INTEGRAL on 2-6 April 2004. In the first months of 2004, the source had increased steadily in optical brightness and had undergone two outbursts. During the latter, occurred in March, it r eached the extreme level of R = 12.1 mag, which triggered our INTEGRAL program. The target has been detected with IBIS/ISGRI up to 60 keV, with a flux of ~3 x 10e-11 erg/s/cm2 in the 30-60 keV interval, a factor of ~2 higher than observed by the BeppoSAX PDS in October 2000. In the field of S5 0716+714 we have also detected the Flat Spectrum Radio Quasar S5 0836+710 and the two Seyfert galaxies Mkn 3 and Mkn 6. Their IBIS/ISGRI spectra are rather flat, albeit consistent with those measured by BeppoSAX. In the spectrum of Mkn 3 we find some evidence of a break between ~60 and ~100 keV, reminiscent of the high energy cut-offs observed in other Seyfert galaxies. This is the first report of INTEGRAL spectra of weak Active Galactic Nuclei.
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168 - C. S. Stalin 2009
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