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Register a new userChanges in the measured image separation of the gravitational lens system, PKS 1830-211
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We present eight epochs of 43 GHz, dual-polarisation VLBA observations of the gravitational lens system PKS 1830-211, made over fourteen weeks. A bright, compact ``core and a faint extended ``jet are clearly seen in maps of both lensed images at all eight epochs. The relative separation of the radio centroid of the cores (as measured on the sky) changes by up to 87 micro arcsec between subsequent epochs. A comparison with the previous 43 GHz VLBA observations (Garrett et al. 1997) made 8 months earlier show even larger deviations in the separation of up to 201 micro arcsec. The measured changes are most likely produced by changes in the brightness distribution of the background source, enhanced by the magnification of the lens. A relative magnification matrix that is applicable on the milliarcsecond scale has been determined by relating two vectors (the ``core-jet separations and the offsets of the polarised and total intensity emission) in the two lensed images. The determinant of this matrix, -1.13 +/-0.61, is in good agreement with the measured flux density ratio of the two images. The matrix predicts that the 10 mas long jet, that is clearly seen in previous 15 and 8.4 GHz VLBA observations (Garrett et al. 1997, Guirado et al. 1999), should correspond to a 4 mas long jet trailing to the south-east of the SW image. The clear non-detection of this trailing jet is a strong evidence for sub-structure in the lens and may require more realistic lens models to be invoked, e.g. Nair & Garrett (2000).
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Measurements of the properties of gravitational lenses have the power to tell us what sort of universe we live in. The brightest known radio Einstein ring/gravitational lens PKS 1830-211 (Jauncey et al., 1991), whilst obscured by our Galaxy at optical wavelengths, has recently been shown to contain absorption at the millimetre waveband at a redshift of 0.89 (Wiklind and Combes, 1996a). We report the detection of a new absorption feature, most likely due to neutral hydrogen in a second redshift system at z = 0.19. Follow-up VLBI observations have spatially resolved the absorption and reveal it to cover the NE compact component and part of the lower surface brightness ring. This new information, together with existing evidence of the unusual VLBI radio structure and difficulties in modeling the lensing system, points to the existence of a second lensing galaxy along our line of sight and implies that PKS 1830-211 may be a compound gravitational lens.
Using the Atacama Pathfinder Experiment (APEX) telescope we have detected the rotational ground-state transitions of ortho-ammonia and ortho-water toward the redshift ~0.89 absorbing galaxy in the PKS 1830-211 gravitational lens system. We discuss our observations in the context of recent space-borne data obtained for these lines with the SWAS and Odin satellites toward Galactic sources. We find commonalities, but also significant differences between the interstellar media in a galaxy at intermediate redshift and in the Milky Way. Future high-quality observations of the ground-state ammonia transition in PKS 1830-211, together with inversion line data, will lead to strong constraints on the variation of the proton to electron mass ratio over the past 7.2 Gyr.
We report on an analysis of X- and $gamma$-ray observations of PKS 1830-211, based on the long-term campaigns carried out by emph{INTEGRAL} and COMPTEL. The emph{INTEGRAL} data currently available present a $33sigma$ significance detection in the 20-100 keV band, while the COMPTEL 6-years data provide a $5.2sigma$ significance detection in the 1-3 MeV energy band. At hard X-rays, emph{INTEGRAL} and supplementary emph{SWIFT} observations show flux variability on timescales of months. At $gamma$-rays, the source shows persistent emission over years. The hard X-ray spectrum is well represented by a power-law model, with $Gamma sim 1.3$ in the 20-250 keV band. This photon index is well consistent with the previous report of $Gamma sim 1.3$ obtained at $E > 3.5$ keV from the best fit of emph{XMM-Newton} data with a broken power law model. The joint emph{XMM-Newton}/emph{INTEGRAL} spectrum presented here is then fit with a broken power-law model and the parameters are refined compared to the previous. The results show the photon index changes from $sim 1.0$ to $sim 1.3$ at a break energy $sim 4$ keV. At MeV energies, the spectrum softens to $Gamma sim 2.2$. These results, together with the EGRET measurement at $E ge 100$ MeV, constitute a broad-band spectrum containing the peak of the power output at MeV energies, similar to most high-luminosity $gamma$-ray blazars. The measured spectral characterstics are then discussed in the framework of the gravitational lens effects.
A 12 year-long monitoring of the absorption caused by a z=0.89 spiral galaxy on the line of sight to the radio-loud gravitationally lensed quasar PKS 1830-211 reveals spectacular changes in the HCO+ and HCN (2-1) line profiles. The depth of the absorption toward the quasar NE image increased by a factor of ~3 in 1998-1999 and subsequently decreased by a factor >=6 between 2003 and 2006. These changes were echoed by similar variations in the absorption line wings toward the SW image. Most likely, these variations result from a motion of the quasar images with respect to the foreground galaxy, which could be due to a sporadic ejection of bright plasmons by the background quasar. VLBA observations have shown that the separation between the NE and SW images changed in 1997 by as much as 0.2 mas within a few months. Assuming that motions of similar amplitude occurred in 1999 and 2003, we argue that the clouds responsible for the NE absorption and the broad wings of the SW absorption should be sparse and have characteristic sizes of 0.5-1 pc.
Gravitational lensing is a potentially powerful tool for elucidating the origin of gamma-ray emission from distant sources. Cosmic lenses magnify the emission from distance sources and produce time delays between mirage images. Gravitationally-induced time delays depend on the position of the emitting regions in the source plane. The Fermi/LAT satellite continuously monitors the entire sky and detects gamma-ray flares, including those from gravitationally-lensed blazars. Therefore, temporal resolution at gamma-ray energies can be used to measure these time delays, which, in turn, can be used to resolve the origin of the gamma-ray flares spatially. We provide a guide to the application and Monte Carlo simulation of three techniques for analyzing these unresolved light curves: the Autocorrelation Function, the Double Power Spectrum, and the Maximum Peak Method. We apply these methods to derive time delays from the gamma-ray light curve of the gravitationally-lensed blazar PKS 1830-211. The result of temporal analysis combined with the properties of the lens from radio observations yield an improvement in spatial resolution at gamma-ray energies by a factor of 10000. We analyze four active periods. For two of these periods, the emission is consistent with origination from the core and for the other two, the data suggest that the emission region is displaced from the core by more that ~1.5 kpc. For the core emission, the gamma-ray time delays, $23pm0.5$ days and $19.7pm1.2$ days, are consistent with the radio time delay $26^{+4}_{-5}$ days.
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