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pks  1830@xmath0211  @xcite consists of two @xmath3 @xcite blazar images separated by 1  and lensed by a @xmath4 @xcite spiral galaxy @xcite . pks  1830@xmath0211  was observed in the radio ( e.g. , * ? ? ? * ; * ? ? ? * ) , infrared ( e.g. , * ? ? ? * ; * ? ? ? * ; * ? ? ? * ) , x - rays @xcite , and gamma - rays @xcite , and the spectral energy distribution of pks  1830@xmath0211  @xcite shows two emission bumps with one in the infrared and the other between the hard x - ray and gamma - ray bands .    the gravitational lens pks  1830@xmath0211  is complicated in many aspects , and one of them is the x - ray absorption . the x - ray absorption was first detected by rosat @xcite . later asca observations @xcite show that the x - ray absorption is variable ; these authors favored a model in which microlensing was the cause of variability . recently , pks  1830@xmath0211  was observed by _ chandra _  and _ xmm - newton _  for five epochs , which enabled us to study the nature of the x - ray absorption in detail combining the angular resolution of _ chandra _  and the large collecting area of _ xmm - newton_. since the two images are resolved by _ chandra _ , we can test the microlensing model predictions and study the x - ray absorption separately for the two lensed images . @xcite found that the differential absorption at the lens galaxy between the two images is @xmath5  . in this paper , we study the time evolution of the absorption in the system from the five _ chandra_and _ xmm - newton _  observations and confirm that the x - ray absorption toward pks  1830@xmath0211  is variable . moreover , we rule out the microlensing interpretation of the observed variability . we observed pks  1830@xmath0211  twice with _ chandra _  and three times with _ xmm - newton_from 2000 to 2004 . the details of the observations are listed in table  [ tab : obslog ] . the _ chandra _ data were reduced with the ` ciao3.2 ` software tools provided by the _ chandra _  x - ray center ( cxc ) following the standard threads on the cxc website . only events with standard _ asca _  grades of 0 , 2 , 3 , 4 , and 6 were used in the analysis . we improved the image quality of the data by removing the pixel randomization applied to the event positions by the standard pipeline . in addition , we applied a sub - pixel resolution technique @xcite to the events on the s3 chip of acis where the quasar images are located . this allowed us to resolve the two lensed images of the blazar . the _ xmm - newton _  data were reduced using the standard analysis software ` sas6.0 ` . we used the tasks ` epchain ` and ` emchain ` from ` sas ` to reduce the pn and mos data , and filtered the events with patterns @xmath6 and @xmath7 for the pn and mos chips , respectively . we fitted the spectra of pks  1830@xmath0211  using ` xspec v11.3.1 ` @xcite in the 0.358 kev observed energy range for _ chandra_spectra and in the 0.3510 kev range for _ xmm - newton _  spectra . in all of our models , we fixed the galactic absorption at @xmath8  @xcite . we analyzed the _ chandra _ spectra of individual images a and b. we modeled the spectra with a power law modified by the galactic absorption and the absorption at the lens redshift ; the fitting results are listed in table  [ tab : indi ] . we experimented with two models where the power law photon indices for the two images were allowed to be different ( model 1 ) and where they were constrained to be the same ( model 2 ) . we assumed that the excess absorption ( above galactic ) arises in the lens galaxy at z=0.886 ( we test this assumption later ) . in both the models , the column densities at the two _ chandra _  epochs for image b are consistently larger than those of image a. in addition , the absorption in the first epoch is consistently larger than that in the second epoch for both images , except for image b in model 1 where it is similar within errors . the photon indices obtained from model 1 fits are similar for the two images and in both epochs , partially due to the large error bars on the parameter caused by the low signal - to - noise ratio of the individual spectra . the photon indices obtained from model 2 show @xmath9 difference from epoch to epoch , which again is not significant . the difference between the absorption in the two images occurs simply because the lines of sight of the two images intersect different parts of the lens galaxy @xcite . the difference between the absorption at the two epochs indicates that the x - ray absorption is variable . the origin of the absorption variability could be either at the lens redshift or at the source redshift . we note that the differential absorption between images b and a is similar in the two epochs , especially in model 2 . this is suggestive of absorption variability occurring at the source redshift . we then analyzed the spectra of the combined images ab for the _ chandra_and _ xmm - newton _  observations . we first fitted the spectra of pks  1830@xmath0211  of the five epochs with a power - law model modified by neutral absorption from the milky way and the lens galaxy . the fitting results are listed in table  [ tab : spec ] ( model 3 ) . we note that the absorption at the lens redshift for this model should be treated as an averaged absorption for the two lines of sight . we also fitted the co - added three _ xmm - newton _  spectra to obtain a higher signal - to - noise ratio spectrum , and the results are also listed in table  [ tab : spec ] . the higher s / n of _ xmm - newton_spectra allows better constraints on the power - law spectral index . we find that the spectral index varies between the _ chandra _  and the _ xmm - newton_observations , though variations within the _ chandra _  epochs and _ xmm - newton _  epochs are smaller . comparing the fitting results of model 3 and model 2 , the spectral index obtained by fitting the combined images ab for the _ chandra _  observations are consistent with results from individual spectral fits in [ sec : indi ] . the absorption at the lens is also variable , especially when comparing the second _ chandra _  observation with other epochs . we further test the variability of the spectra by comparing a model with no spectral variability ( with the exception of normalization ) and another model with variable absorption and spectral index . we found that the model with the spectral variability produced a better fit with a @xmath10 improvement of 56.1 ( a null probability of @xmath11 by the f - test ) when jointly fitting the five x - ray observations . when we only consider the three _ xmm - newton _  observations , the corresponding improvement is 14.5 with a null probability of 0.0097 given by the f - test . the largest absorption variation is @xmath12 between the second _ chandra _  epoch and the first _ xmm - newton _  epoch . although the variable spectral index in blazars is common ( e.g. , * ? ? ? * ) , the absorption at the lens galaxy is unlikely to vary on the time scales of years . as discussed in   [ sec : indi ] , it is more likely that the variable absorption component is at the source redshift close to the agn , where a short time - scale variability is possible and may be expected . the next model we tried is a power - law modified by three absorption components , the galactic absorption and the absorptions at the lens and the source . we fixed the absorption at the lens as @xmath13  , the smallest absorption column density detected in the five epochs from the previous model . this is the largest absorption column density at lens we can set to ensure no absorption variability at the lens galaxy . the fitting results are listed in table  [ tab : spec ] ( model 4 ) . again we detected variability of both the photon index and the absorption at the source redshift . using the same test that we described in the previous model , we found that the model allowing spectral variability improved the @xmath10 by 59.8 with a null probability of @xmath14 for jointly fitting the five x - ray observations , and an improvement of 14.7 with a null probability of 0.01 for jointly fitting the three _ xmm - newton _  observations . the largest absorption variation for this model is @xmath15 between the second _ chandra _  epoch and the first _ xmm - newton _  epoch . the variable absorption in this model can be naturally associated with outflows from the central engine . although , this model produces comparable fits for the two _ chandra _  spectra compared with model 3 , where there is no absorption at the source redshift , the fits for the _ xmm - newton _  spectra with a higher s / n are worse than model 3 with @xmath10 increases of 5.8 , 37.2 , 13.0 for the three _ xmm - newton _  spectra . we also tested whether fitting the absorption component at the source with a warm absorber or a partially covering absorber would improve the fit . while the warm absorber model produces a worse fit , the partial covering model ( table  [ tab : spec ] , model 5 ) produces comparable fits to model 3 . for the partial covering model , the model allowing spectral variability produces improvement of the @xmath10 by 79.7 with a null probability of @xmath16 for jointly fitting the five x - ray observations , and an improvement of 14.1 with a null probability of 0.01 for jointly fitting the three _ xmm - newton _  observations . the largest absorption variation for this model is @xmath17 , again , between the second _ chandra _  epoch and the first _ xmm - newton _  epoch .    as a final improvement to our model , we assume that the lines of sight of the two lensed images pass through different locations in the lens galaxy and thus have different absorption column densities . this differential absorption is measured as @xmath5  @xcite . therefore , we have a model composed of two power - law components and each of them is modified by three absorptions from galactic , lens , and source . the two power - law components representing the two lensed images have the same photon index but different normalizations . the normalization ratio between images a and b is constrained as @xmath18 by taking the hard x - ray flux ratios ( 38 kev ) from the _ chandra _  observation . the galactic absorption and the absorption at the source are the same for the two power - law components , and the absorbers at the source are assumed to be partially covering the continuum . the absorber column densities at the lens are different for the two power - law components by the amount given by @xcite . we fit the two _ chandra _  spectra and the co - added _ xmm - newton _  spectrum simultaneously with this model . we constrained that the absorption at lens did not vary . the fitting results are listed in table  [ tab : spec ] ( model 6 ) , and the spectra are shown in figure  [ fig : spec ] . the fitting results indicate that the absorption at the source has varied by roughly @xmath19 . we detected the variable absorption , variable power - law photon index , and variable flux for the blazar pks  1830@xmath0211 . the observed variability between _ chandra _  and _ xmm - newton _  spectra could be , in part , due to imperfect cross - calibration between the two . however for high s / n spectra , the cross - calibration between _ chandra _  and _ xmm - newton _  can yield a spectral difference of @xmath20 0.03 , whereas our measured differences are between @xmath20 0.150.3 . in addition , the higher s / n _ xmm - newton _  spectra show a statistically significant variability within the three _ xmm - newton _  observations ( @xmath10 improvement of 14.5 , 14.7 , and 14.1 for models 3 , 4 , and 5 with spectral variability ) . we also found the spectral variability between the two _ chandra _  observations , where the second _ chandra _  epoch has consistently lower absorption column densities than the first observation . this is better demonstrated in   3.1 , where we analyzed the individual spectra of each image . we plot the variations of absorption in figure  [ fig : nh ] , photon index variations in figure  [ fig : gamma ] , and the photon index against unabsorbed flux in figure  [ fig : gammaf ] . it is well known that blazars are variable , so the observed spectral variability is not surprising in itself . we also found that the photon index and flux are correlated ( figure  [ fig : gammaf ] ) . this relation has been observed in several gamma - ray loud agns ( foschini et al . pks  1830@xmath0211  provides an additional example of a source following this correlation . the variable absorption is more intriguing . the variable absorption toward pks  1830@xmath0211  was detected previously with _ observations @xcite , although interpreted differently . @xcite obtained a variation amplitude of @xmath21 when modeling the absorption at the lens , which is consistent with our measurement of @xmath22 ( model 3 ) . we note that the variation detected by @xcite is on the timescale of 10 days while that found by us is on the timescale of years . it is possible that the variable absorption is at the source redshift . depending on the nature of the absorber , we obtained variations of @xmath23 and @xmath24 for a fully covering absorber ( model 4 ) and a partially covering absorber ( model 5 , 6 ) , respectively . the other possibilities are microlensing models . @xcite proposed a microlensing interpretation to explain the apparent variable absorption . the basic idea is that the absorption does not vary but is different for the two images , and the microlensing produces flux changes between the two images which appears as variable absorption . as we discussed in the spectral fits to individual _ chandra _ images (   [ sec : indi ] ) , the absorption varies in individual images between the two epochs , which can not be attributed to this simple microlensing model . for this reason , we rule out the simple microlensing model as the cause of variable absorption in pks  1830@xmath0211 . more complicated microlensing models are required which must involve significant emission size differences between the soft and hard x - ray regions to interpret the data . however , even these models will have difficulty explaining the similar differential absorptions between images a and b for the two _ chandra _  epochs . microlensing will only produce uncorrelated changes between the images . variable absorption thus appears to be a robust result , independent of model . the variability can either come from the lens or from the source redshift . if the variable absorption is at the lens , a variability amplitude of @xmath22 can sufficiently parameterize the _ chandra _  and _ xmm - newton _  spectra without invoking any absorption at the source . recently , variable mg  ii absorption has been detected in an intervening absorber in front of a gamma - ray burst @xcite . the observed mg  ii column density changes as the burst expands geometrically @xcite . similarly , if the size of the blazar changes with luminosity , it may produce variable absorption at the lens . another mechanism that can produce variable absorption at the lens galaxy is proposed by @xcite , where microlensed images , slightly shifted from the original image position , intersect slightly different positions at the lens , producing variable absorption . however , in pks  1830@xmath0211 , the differential absorption of the two images in the two _ chandra _  epochs is similar , arguing against the variability at the lens . it is far more likely that the variable absorption is intrinsic to the blazar , simply because there are other agns with variable intrinsic absorption , including blazars ( see below ) .    while the absorption toward the gravitational lens pks  1830@xmath0211  is very complicated , with the sequence of _ chandra _  and _ xmm - newton _  observations , a converging picture is emerging . besides the galactic absorption of @xmath25 @xcite , there is also an intrinsic absorption and absorption from the lens galaxy . the absorption column densities in the lens galaxy are different for the two lensed images by @xmath26  @xcite , and this is consistent with the differential extinction measurement between the two images and a galactic dust - to - gas ratio . the amplitude of the variability of the intrinsic absorption is model dependent with amplitudes of @xmath1@xmath2 . recently , the intrinsic absorption for blazars has been reported in several cases , such as gb  b1428 + 4217 @xcite , pmn  j0525@xmath03343 @xcite , and rbs  315 ( piconcelli & guainazzi 2005 ; see also tavecchio et al . 2007 ) . in this paper , we present variable intrinsic absorption toward gravitationally - lensed blazar pks  1830@xmath0211 . the large variation in the absorption column density can be interpreted as outflows similar to those detected in bal  qsos . however , as pks  1830@xmath0211  is a blazar , this outflow must be in the polar direction . recent numerical simulations of accretion flows in agns @xcite discussed the cases of polar outflows ; our observations of pks  1830@xmath0211  might be providing an example in support of such models . in addition , it is also possible that the intrinsic absorption variation is caused by the interaction between the blazar jet and its environment , or the variation from the geometric configuration of the jet . more intense monitoring of this system or further variability studies using a large sample of blazars are needed to better constrain the nature of their x - ray spectral variation . hao , h. , stanek , k. z. , dobrzycki , a. , matheson , t. , bentz , m. c. , kuraszkiewicz , j. , garnavich , p. m. , howk , j. c. , calkins , m. l. , worthey , g. , modjaz , m. , & serven j. 2006 , apj letter submitted , astro - ph/0612409              mori , k. , tsunemi , h. , miyata , e. , baluta , c. , burrows , d. n. , garmire , g. p. , & chartas , g. 2001 , in asp conf . ser . 251 , new century of x - ray astronomy , ed . h. inoue & h. kunieda ( san francisco : asp ) , 576                            cccc 2000 - 06 - 26 & _ chandra _ & hetgs & 47471 + 2001 - 06 - 25 & _ chandra _ & hetgs & 51219 + 2004 - 03 - 10 & _ xmm - newton _ & none & 8328 + 2004 - 03 - 24 & _ xmm - newton _ & none & 27004 + 2004 - 05 - 05 & _ xmm - newton _ & none & 21356 +      2000 - 06 - 26 & a & @xmath27 & @xmath28 & 100.5(108 ) + 2000 - 06 - 26 & b & @xmath29 & @xmath30 & 129.6(106 ) + 2001 - 06 - 25 & a & @xmath31 & @xmath32 & 140.7(120 ) + 2001 - 06 - 25 & b & @xmath33 & @xmath34 & 113.8(116 ) + 2000 - 06 - 26 & a & @xmath27 & @xmath35 & 229.6(215 ) + 2000 - 06 - 26 & b & @xmath36 & & + 2001 - 06 - 25 & a & @xmath37 & @xmath38 & 255.2(237 ) + 2001 - 06 - 25 & b & @xmath39 & & +      date & 2000 - 06 - 26 & 2001 - 06 - 25 & 2004 - 03 - 10 & 2004 - 03 - 24 & 2004 - 05 - 05 & + ( @xmath40 ) & @xmath41 & @xmath42 & @xmath43 & @xmath44 & @xmath45 & @xmath46 + @xmath47 & @xmath48 & @xmath49 & @xmath50 & @xmath51 & @xmath52 & @xmath53 + unabsorbed flux & @xmath54 & @xmath55 & @xmath56 & @xmath57 & @xmath58 & @xmath59 + @xmath60 & 365.6(305 ) & 365.6(337 ) & 151.8(152 ) & 447.3(396 ) & 314.3(301 ) & 843.7(743 ) + ( @xmath61 ) & @xmath62 & @xmath63 & @xmath64 & @xmath65 & @xmath66 & @xmath67 + @xmath47 & @xmath68 & @xmath69 & @xmath70 & @xmath71 & @xmath53 & @xmath51 + unabsorbed flux & @xmath72 & @xmath55 & @xmath56 & @xmath73 & @xmath58 & @xmath59 + @xmath60 & 369.9(305 ) & 365.6(337 ) & 157.6(152 ) & 484.5(396 ) & 327.3(301 ) & 899.3(743 ) + ( @xmath61 ) & @xmath74 & @xmath75 & @xmath76 & @xmath77 & @xmath78 & @xmath79 + covering factor & 0.44 ( fixed ) & 0.44 ( fixed ) & @xmath80 & @xmath81 & @xmath82 & @xmath83 + @xmath47 & @xmath84 & @xmath85 & @xmath86 & @xmath87 & @xmath87 & @xmath88 + unabsorbed flux & @xmath72 & @xmath89 & @xmath90 & @xmath91 & @xmath92 & @xmath93 + @xmath60 & 370.6(305 ) & 365.9(337 ) & 137.4(151 ) & 447.4(395 ) & 315.6(300 ) & 827.0(742 ) + @xmath94 ( @xmath40 ) & + ( @xmath61 ) & @xmath95 & @xmath75 & & & & @xmath96 + covering factor & + @xmath47 & @xmath97 & @xmath98 & & & & @xmath99 + @xmath60 & +
we present x - ray spectral analysis of five _ chandra _  and _ xmm - newton_observations of the gravitationally - lensed blazar pks  1830@xmath0211  from 2000 to 2004 . 
 we show that the x - ray absorption toward pks  1830@xmath0211  is variable , and the variable absorption is most likely to be intrinsic with amplitudes of @xmath1@xmath2 depending on whether or not the absorber is partially covering the x - ray source . 
 our results confirm the variable absorption observed previously , although interpreted differently , in a sequence of _ asca _  observations . 
 this large variation in the absorption column density can be interpreted as outflows from the central engine in the polar direction , consistent with recent numerical models of inflow / outflows in agns . 
 in addition , it could possibly be caused by the interaction between the blazar jet and its environment , or the variation from the geometric configuration of the jet . while the spectra can also be fitted with a variable absorption at the lens redshift 
 , we show that this model is unlikely . 
 we also rule out the simple microlensing interpretation of variability which was previously suggested .