Instruct: Identify the main and secondary category of Arxiv papers based on the titles and abstracts
Query: A partially occulting MACHO-microlensing event in the Twin Quasar
  Q0957+561   A doubly-peaked quasar microlensing event in the lensed Twin Quasar Q0957+561
A,B (Colley and Schild 2003) is analysed within several lensing models. In the
most realistic model a lens resolves in image B the ellipse shaped, bright
inner rim of the quasar's accretion disk, intersecting it twice. This lens
weighs 0.5 Earth mass and is located inside the Galaxy, at 3 kpc distance.
During the passing, it partially occults the source, which allows to describe
it as a primordial gas cloud of 1.4 Solar radius and 17 K temperature, in
accordance with the theory of Gravitational Hydrodynamics. Lensing by such
objects against the Magellanic Clouds and Galactic centre will also lead to
occultation dips.

15
The categories of this paper are: nucl-ex
28
The categories of this paper are: alg-geom
8
The categories of this paper are: hep-ex
1
The categories of this paper are: cs
25
The categories of this paper are: patt-sol
27
The categories of this paper are: comp-gas
5
The categories of this paper are: gr-qc
12
The categories of this paper are: nucl-th
13
The categories of this paper are: quant-ph
20
The categories of this paper are: acc-phys
14
The categories of this paper are: math-ph
9
The categories of this paper are: nlin
17
The categories of this paper are: q-fin
29
The categories of this paper are: funct-an
23
The categories of this paper are: solv-int
31
The categories of this paper are: ao-sci