latest optical observations of radio and x-ray emitting ...jonathan/jets/04-05_aas-poster.pdf ·...

TXS 1828+487 (z = 0.692)0.5-7 keV image, 4.8 GHz contours

Extended X-ray emission.

PKS 1655-776 (z = 0.094)0.5-7 keV image, 8.6 GHz contours

Extended X-ray emission is not detected.



PKS 1655+077 (z = 0.621)0.5-7 keV image, 1.4 GHz contours






















Latest Optical Observationsof Radio and X-ray Emitting Quasar Jets

Jonathan Gelbord, Herman L. Marshall (MIT), D.A. Schwartz (SAO), D.M. Worrall, M. Birkinshaw (U. Bristol & SAO), E.S. Perlman (UMBC), J.E.J. Lovell, D.L. Jauncey (CSIRO), D.W. Murphy & R.A. Preston (JPL)

We are conducting a Chandra survey of a large, radio-selected sample of flat-spectrum radio quasars with extended radio structure. X-ray emission has now been discovered from 60% of our jet systems, with over half of the sample now observed. In support of this survey we have an ongoing program to obtain both spectroscopic and imaging data with the Magellan 6.5m telescopes. We provide an update on this optical program below, following a summary of our X-ray findings to date.

PKS 2123-463(z=1.670)

Magellan observations

PKS 1202-262 (z = 0.789)0.5-7 keV image, 8.6 GHz contours; extended X-ray emission.

PKS 1046-409 (z = 0.620)0.5-7 keV image, 8.6 GHz contours; X-ray emission.

PKS 1258-321 (z = 0.017)0.5-7 keV image, 8.6 GHz contours; extended X-ray emission is not detected.

PKS 1145-676 (z = ?)0.5-7 keV image, 8.6 GHz contours; extended X-ray emission is not formally detected.


8.6 GHz radiocontours.


The red contour is 3x the RMS backgroundAround the border: 0.5-7 keV images of our Chandra cycle 3 targets with overlaid radio contours. All data are convolved to the same resolution: 1.2” fwhm. X-ray images all use the same logarithmic stretch to show intensity. Radio frequencies are indicated for each figure; contour are set at the background RMS level times 5, 10, 20, etc.

Background: The Chandra surveyThe sampleWe selected 56 flat spectrum radio quasars* whose extended (> 2” from the core) 5 GHz flux met either of two criteria: a flux limit or one-sided, linear morphology..* FSRQs are quasars with a radio spectral index a < 0.5, where Fn µ n-a.

Initial observations t 5 ks snapshot observations of 20 targets were made

with Chandra during Cycle 3. t New sub-arcsecond radio maps were obtained for all

20 sources using the VLA and ATCA.The 0.5-7 keV X-ray images of these 20 systems are shown with overlaid radio contours as the border of this poster.

The continuation t Ten more quasar jet systems have been scheduled

during the current cycle 5. t Seven other sample members have data in the public

archive. (Most are part of the survey by Sambruna et al. 2004, ApJ accepted, astro-ph/0401475)

The Latest observationsSeven of our ten cycle 5 targets have been observed so far. Of these, three show clear evidence of X-ray jet emission: PKS 1055+201, PKS 1421-490, and PKS 2123-463 (the other four appear to be non-detections, but we have not yet subjected them to rigorous analysis).

PKS 1055+201(z=1.110)

21.3”

PKS 1421-490z unknown

5.8”

Initial resultsThe results for our Cycle 3 targets are presented in Marshall et al. 2004 (in prep; just days from submission...). We find... u ...12 out of 20 systems have extended X-ray structures in the same direction as the radio jet. The detection rate is

63% including the archival data. u ...similar X-ray and radio morphologies. X-ray hot spots usually agree with radio peaks (but see PKS 2101-490); X-

ray flux often follows radio jets through gradual bends (e.g., PKS 1202-262) but usually ends when the radio map shows a sharp turn (with the notable exception of PKS 1030-357).

u ...X-ray fluxes are consistent with inverse Compton scattering of the cosmic microwave background (the IC-CMB model; Tavecchio et al. 2000, ApJ 544, L23; Celotti et al. 2001, MNRAS 321, L1). Fitting such models to the jets suggests magnetic fields of order B ~ 10-5 Gauss and alignments close to our line of sight implying deprojected lengths of hundreds of kpc (Marshall et al. 2004, in prep.; Schwartz et al. 2003, New Ast. Rev. 47, 461). However, we do not see the predicted correlation between arx and redshift, suggesting that if the IC-CMB model is correct, then the distribution of other parameters (Lorentz factor, orientation) must cause scatter.

The radio to X-ray spectral slope does not appear to be correlated with redshift. The dashed line gives the dependence of arx on z under the assumptions that the X-ray emission results only from inverse Compton scattering off the cosmic microwave background and that the beaming parameters are the same as those of PKS 0637-753, in which case the X-ray flux density would increase as (1 + z)4.

PKS 1421-490

PKS 1421-490 was the only member of our sample without an identified optical counterpart. We observed it with Magellan in three filters last spring, discovering a 24th magnitude source at the radio position. The g’-r’ and r’-i’ colors are consistent with quasars at 2.5 < z < 3.0 (Richards et al. 2002, AJ 123, 2945), which would make this the most distant source in our sample.

We have identified the optical counterpart of PKS 1421-490, and have

discovered that the jet is optically dominated and uniquely powerful.

The optical image is shown at left. Amazingly, we find an optical counterpart to the first jet knot that is more than five magnitudes brighter than the core! No other jet we’ve observed is within five magnitudes of their respective cores. The broad-band SED (right) illustrates the optical dominance of this feature.We consider it unlikely that this bright optical source is a foreground object. We have obtained a low S/N spectrum and found it to be featureless, suggesting a non-thermal continuum. Besides, this feature is also brighter than the radio core in X-rays (see image above). In the radio band the core is securely identified by its flat spectrum and compact size.

SED plot showing the flux of the core and first jet knot of PKS 1421-490. The data are still preliminary, but clearly show the

strong excess optical flux.

Magellan i’ image of PKS 1421-490. The core is the strongest radio peak; in the optical, the first jet knot is 200-300 times brighter.

RGB composite image of PKS 1421-490 field, observed by us using Magellan with three filters: i’ (red), r’ (green), and g’ (blue). Field shown here is approximately 1.5’ ¥ 0.75’. The 0.4” error circle for the position

of the quasar core is shown.

atmosphericabsorption

Mg II

[Ne V] (??)

PKS 2101-490Flux

Spectrum observed with the LDSS2 spectrograph. This is the composite of three 100 s exposures using the medium red grism (300 l/mm).

The spectrum exhibits a strong line at 5713 Å with a Gaussian fwhm of ~200 Å. There are no other strong features in the 4300-9500 Å band. The absence of other strong features in such a wide spectral range indicates that the observed line is Mg II 2799. A tentative second line at 6991 Å, if confirmed, could be identified as [Ne V] 3426.

Magellan g’ image combining five 300 s exposures with the MagIC camera, with 8.6 GHz radio

contours overlaid. No counterpart to the jet is detected down to g’ ~ 25.

PKS 2101-490We measure a redshift of 1.04 for PKS 2101-490.

Of the 56 quasars in our sample, four did not have known redshifts. PKS 2101-490 is the first of these to be observed spectroscopically.

Non-detection of other jetsAside from PKS 1421-490, we have made imaging observations of 9 other jet systems with X-ray detections. The optical flux limits obtained for the quasar jets provide strong constraints for the jet emission models.

PKS 1202-262Magellan g’ image8.6 GHz ATCA contours

5.4”

SED plot (right) for the three regions of PKS 1202-262 indicated on the image above. If the X-ray

flux is synchrotron in origin, simple models predict a power law

continuum from radio to X-rays (dashed lines). Such models are contradicted by the optical flux limits. Similar constraints are

obtained for all observed systems except for PKS 1421-490.

The optical upper limits rule

out simple synchrotron

models, favoring instead inverse

Compton scattering as the origin of the jet X-ray emission.

latest optical observations of radio and x-ray emitting ...jonathan/jets/04-05_aas-poster.pdf ·...

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