Differences

This shows you the differences between two versions of the page.

--- evn:evn_science [2018/03/15 14:01] – [Introduction] antonis
+++ evn:evn_science [2018/09/12 09:19] – [Gravitationally-lensed radio arcs observed with global VLBI] antonis
@@ Line 17: / Line 17: @@
-[[http://www.jive.eu/jivewiki/doku.php?id=evn:guidelines|The next deadline is June 1, 2018]].
+[[http://www.jive.eu/jivewiki/doku.php?id=evn:guidelines|The next deadline is October 1, 2018]].
@@ Line 34: / Line 34: @@
 \\
+=====Gravitationally-lensed radio arcs observed with global VLBI=====
+The Strong lensing at High Angular ResoluTon Program (SHARP) led by McKean (ASTRON) has
+obtained a deep global VLBI observaTon of the gravitaTonal lens MG J0751+2716 at 1.65 GHz
+(project GM070; PI: McKean). The 18.5 hours observation used 24 antennas from the EVN and
+the VLBA, including the large apertures (> 50 m) of the Lovell, Effelsberg, Robledo and Green Bank
+telescopes. Data were recorded at 512 Mbps and correlated at JIVE to produce 8 spectral
+windows (IFs) with 8 MHz bandwidth and 32 channels each, through both circular polarisaTons.
+MG J0751+2716 is one of the few quadruply imaged radio-loud gravitationally lensed quasars that
+show extended arcs on VLBI-scales. The global VLBI L-band deep imaging detects all of the extended
+arcs at high significance, showing the complex surface brightness structure of the background
+source in unprecedented detail (see Figure from [[https://doi.org/10.1093/mnras/sty1326|Spingola et al (2018)]]). Because of the complexity of this system, the imaging was
+performed using multi-scale cleaning within the wsclean algorithm (Offringa et al. 2014). The total
+flux density of the target is 350 mJy and the off-source rms is 41 μJy/beam. Never before have such
+extended (200-600 mas) gravitaTonal arcs been detected at an angular resoluTon of a few mas. The
+excellent uv-coverage and surface brightness sensiTvity provided by the global VLBI array have been
+fundamental for a precise study of the structure of the extended arcs on mas-scales from
+MG J0751+2716.
+{{:evn:grav_lens_spingola.jpeg?400|}}
+**Figure 1.**Global VLBI imaging of MG J0751+2716 at 1.65 GHz (Spingola et al. (2018)). The off-source
+rms is 41 μJy/beam and the peak surface brightness is 2.9 mJy/beam. The restored beam is 5.5x1.8
+mas, and is shown within the white box in the bottom-hand corner.
+Spingola et al. (2018) analysed these observations and identified lensed emission corresponding to the same source component, providing a very large number of constraints on the mass model that also sampled a large radial and tangential extent. When performing the mass modelling of this system, they found a discrepancy between the observed and predicted positions of the lensed images, with an average position rms of the order of 3 mas, which is much larger that the measurement errors (40 μas on average). A possible explanation for the offset between the observed and model-predicted positions is the presence of some additional mass structure (e.g. Metcalf & Madau 2001). However, since the lensing galaxy lies in a small group of galaxies, it is not clear whether this extra mass is in the form of sub-haloes within the lens or along the line of sight, or from a more complex halo for the galaxy group. Furthermore, the lens mass model suggests an inner density slope for the main lensing galaxy that is steeper than isothermal. This is consistent with studies of other low-mass early-type satellite galaxies in dense environments, and is in agreement with the two-phase galaxy formation scenario (Guo & White 2008).
 ===== The Repeating Fast Radio Burst FRB 121102 as seen on milliarcsecond angular scales =====
 [[http://www.nature.com/nature/journal/v541/n7635/full/nature20797.html | Chatterjee et al. (2017) ]] has been able to locate (with a 100 mas precision) the repeating FRB 121102. This has led to its unambiguous association with persistent radio and optical counterparts, and to the identification of its host galaxy. However, an even more precise localization is needed in order to probe the direct physical relationship between the millisecond bursts themselves and the associated persistent emission.