The case for gravitational millilensing in the multiply–imaged quasar B1152+199. (arXiv:1811.06053v1 [astro-ph.GA])
<a href="http://arxiv.org/find/astro-ph/1/au:+Asadi_S/0/1/0/all/0/1">Saghar Asadi</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Zackrisson_E/0/1/0/all/0/1">Erik Zackrisson</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Varenius_E/0/1/0/all/0/1">Eskil Varenius</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Freeland_E/0/1/0/all/0/1">Emily Freeland</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Conway_J/0/1/0/all/0/1">John Conway</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Wiik_K/0/1/0/all/0/1">Kaj Wiik</a>
Previous Very Long Baseline Interferometry (VLBI) observations of the quasar
B1152+199 at 5GHz has revealed two images of a strongly lensed jet with
seemingly discordant morphologies. Whereas the jet appears straight in one of
the images, the other exhibits slight curvature on milliarcsecond scales. This
is unexpected from the lensing solution and has been interpreted as possible
evidence for secondary, small-scale lensing (millilensing) by a compact object
with a mass of $~10^5$-$10^7 M_odot$ located close to the curved image. The
probability for such a superposition is extremely low unless the millilens
population has very high surface number density. Here, we revisit the case for
millilensing in B1152+199 by combining new global-VLBI data at 8.4GHz with two
datasets from the European VLBI Network (EVN) at 5GHz (archival) and at 22GHz
(new dataset), and the previously published 5GHz Very Long Baseline Array
(VLBA) data.
We find that the new data with a more circular synthesized beam, exhibits no
apparent milliarcsecond-scale curvature in image B. Various observations of the
object spanning $sim$15 years apart enable us to improve the constraints on
lens system (thanks also to the improved astrometry resulting from 22GHz
observations) to the point that the only plausible explanation left for the
apparent curvature is the artifact due to the shape of the synthesized beam.
Previous Very Long Baseline Interferometry (VLBI) observations of the quasar
B1152+199 at 5GHz has revealed two images of a strongly lensed jet with
seemingly discordant morphologies. Whereas the jet appears straight in one of
the images, the other exhibits slight curvature on milliarcsecond scales. This
is unexpected from the lensing solution and has been interpreted as possible
evidence for secondary, small-scale lensing (millilensing) by a compact object
with a mass of $~10^5$-$10^7 M_odot$ located close to the curved image. The
probability for such a superposition is extremely low unless the millilens
population has very high surface number density. Here, we revisit the case for
millilensing in B1152+199 by combining new global-VLBI data at 8.4GHz with two
datasets from the European VLBI Network (EVN) at 5GHz (archival) and at 22GHz
(new dataset), and the previously published 5GHz Very Long Baseline Array
(VLBA) data.
We find that the new data with a more circular synthesized beam, exhibits no
apparent milliarcsecond-scale curvature in image B. Various observations of the
object spanning $sim$15 years apart enable us to improve the constraints on
lens system (thanks also to the improved astrometry resulting from 22GHz
observations) to the point that the only plausible explanation left for the
apparent curvature is the artifact due to the shape of the synthesized beam.
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