EVN observations of GPS radio sources Liu X. Urumqi Observatory, NAOC

Urumqi 25m telescope Antenna surface accuracy 0.4mm (rms), Could contribute to EAVN at 8.4, 22 GHz, 8.4 GHz SEFD~500Jy, RCP only, A new 22 GHz receiver is under construction, could be completed at end of 2009, or 2010, will have dual polarization.

GPS/CSS sources Useful working definitions: GPS (gigahertz peaked spectrum) sources, CSS (compact steep spectrum) sources, samples are founded since 1980’s. They make up of 10%, 30% respectively in cm-wavelength radio sources population. GPS sources are powerful and compact (<1kpc), have a convex radio spectrum that peakes between GHz, those peak at >5 GHz are called HFPs (high frequency peakers). CSS sources, are larger (1-20kpc), and have convex spectrum that tends to peak at lower frequencies. See O’Dea 1998, and 4th CSS/GPS workshop proceedings (AN 2009).

Why: peaked spectrum in GPS/CSS? The turnover, is due to absorption, either by SSA or by FFA, or even both

Cotton et al. 2003

CSO to MSO to LSO(GRS) CSO(compact symmetric object), MSO(medium-sized symmetric object), LSO(large-sized symmetric object), GRS(giant radio sources). CSO < 1 kpc  MSO kpc  LSO kpc

GPS: baby radio sources By measuring of proper motions in GPS sources, ages of a dozen of GPS sources are estimated at s yrs, so it is important in understanding of the very early phase of radio activity of AGN. Polatidis & Conway 2003.

On existing samples List of GPS sources O’Dea et al. 1991, de Vries et al. 1997, Labiano et al Stanghellini et al. 1998, a complete bright GPS sample in northern sky, Snellen et al. 2002, a complete bright GPS (galaxy) sample in southern/equator sky. GPS sources are composed of galaxies and quasars, they show very different property, except the similar convex radio spectrum. Most GPS galaxies have CSO-like structure, have no or very low (<0.5%) fractional polarization, while GPS quasars are often core-jet structure and have pretty high polarization to a few percent. See Stanghellini et al. 1997; Liu et al. 2006, Majority GPS galaxies are stable in flux, but most GPS quasars are variable (Torniainen et al. 2005; Liu et al. 2009), it is argued that some of GPS quasars are not genuine GPS sources (Torniainen et al. 2005), which may appear as a GPS source in a short time.

Galaxy-type GPS sample Snellen 2002 sample, 49 sources in -40 to 15 declination, \b\>20deg, with S2.7>0.5Jy. We have build up a sub-sample with conditions: 1, no vlbi images availble, 2, declination >5deg, 15 sources are selected. We have completed EVN observations at 1.6 GHz (Liu et al. 2007) and at 5 GHz (this talk), and single dish flux monitoring of these sources at 5 GHz with Urumqi 25m telescope. We want to study the galaxy GPS sources in: vlbi structure, spectrum, and size distribution, viewing angle of jets, and flux variability etc.

EVN observation of 12 GPS sources at 5 GHz (EVN code EL036)

Flux variation >10%

Summary of the preliminary results Majority of the GPS galaxies show compact double or CSO like VLBI structure, the spectra of the VLBI components show steep or inverted, indicating they are lobes/hotspots, two sources probably show proper motion of lobes, from 1.6 GHz image in 2006 to 5 GHz image in 2008, suggesting they very young sources if the proper motions are true. Two sources show core-jet like VLBI structure, as also indicated by flux density variability.

Joint Bonn-Urumqi project on IDV observations of AGN at 5 GHz

IDV monitoring at Urumqi name id alfa(2000) dec(2000) len tim sub flux Var.Index 3C48 p % i ,3.1,1.1 var CTA21 c ,0.5,0.2 good OJ287 i , 1.79% var i ,0.87% c ,0.2% i %,1.1 IDV c ,0.26% i ,2.6% IDV c %, 0.56% i ,2.92% strong IDV i ,3.3% IDV 3C286 p %,0.54% NGC7027 p %,0.31%

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Quasar B

Monitoring of Fermi AGNs is just preparing. Thank you!