Time delays in PG 1115+080: new estimates

Abstract

We report new estimates of the time delays in the quadruple gravitationally lensed quasar PG 1115+080, obtained from the monitoring data in filter R with the 1.5‐m telescope at the Maidanak Mountain (Uzbekistan, Central Asia) in 2004–2006. The time delays are 16.4 d between images C and B and 12 d between C and A1+A2, with image C leading for both pairs. The only known estimates of the time delays in PG 1115 are those based on observations by Schechter et al. –23.7 and 9.4 d between images C and B, and C and A1+A2, respectively, – and as revised by Barkana –25 and 13.3 d for the same image components, but with the use of another method. The new values of time delays in PG 1115+080 may be expected to provide larger estimates of the Hubble constant, thus decreasing a diversity between the H0 estimates taken from gravitationally lensed quasars and those taken from other methods.

PG 1115+080: variations of the A2/A1 flux ratio and new values of the time delays

“…The largest differences are for τ BC and τ BA : Table 3. The time delays (d) for PG 1115+080 as reported earlier and in our previous work (Vakulik et al 2009 our estimate of τ BC is a factor of 1.5 smaller, while for τ BA , it is almost three times smaller as compared to the results of Schechter et al (1997) and Barkana (1997). Meanwhile, our values of τ AC are rather similar to those of Schechter and, especially, of Barkana.…”

“…In we report our measurements of the A2/A1 flux ratios in filters V , R and I from our data obtained in 2001, 2002 and 2004–2006 at the Maidanak Observatory and analyse their behaviours in time and in wavelength. In , we analyse the new estimates of the time delays between the PG 1115+080 images, obtained from our monitoring in the R filter during 2004–2006 and reported in Vakulik et al (2009). The new values differ noticeably from those reported by Schechter et al (1997) and Barkana (1997).…”

“…As far as can be expected from Table 3, the three measurements of time delays do not provide the time delay ratios consistent with each other and with model predictions. This can be seen from Table 4, where we collected several model predictions for r ABC together with the measurements presented by Schechter et al (1997), Barkana (1997) and Vakulik et al (2009). Furthermore, we presented here the time delay ratios r CBA = τ AC /τ BC , which are connected with r ABC by a relationship r CBA = r ABC /(1 + r ABC ).…”

“…To test our method for robustness and absence of systematics, and to estimate the accuracy inherent in our time delay measurements, we fulfilled a numerical simulation as described in detail in Vakulik et al (2009). The simulated light curves of the components were obtained by shifting the approximating curve f ( t i , Δ t , τ j ) by the proper time delays τ 1 , τ 2 and magnitude differences, and by adding random quantities to imitate the photometry errors.…”

“…The light curves of images A, B and C shifted by the corresponding time delays and reduced to image A in magnitude are shown in fig. 2 from our previous paper (Vakulik et al 2009) for the approximating function parameter Δ t = 0.12 yr. As is seen from this picture, the data points for all the three images are very well consistent with each other and with the approximating curve.…”