90. Unidentified extended sources of gamma ray emission

Here is another open problem in astrophysics , as far as I understand…

The H.E.S.S. system of telescopes in Namibia is among most successful instruments of its kind.

In particular, it has very large field of view allowing to discover new sources of gamma ray emission. Many of discovered sources were identified with known objects such as SN remnants,  pulsars, star clusters etc. Sometimes a gamma-ray emission source discovered by H.E.S.S. was in one-to-one correspondence with some object from the class of potential gamma-ray emitters, sometimes – not.

The source HESS J1503-582 is among the latter:

First of all one has to look for traditional sources of GR emission. There is a pulsar PSR J1502-5828 nearby, but it is to old to produce so powerful flux: neighbouring variable star AX J1504.6-5824 is also excluded as a source of the flux. This pretty much covers all the catalogue of sources, so the authors of the paper started to look for any other objects in this direction and found what is called “forbidden-velocity-wing” (FVW).

FVWs are wings of line emission at velocities forbidden by the canonical Galactic rotation curve in limited spatial regions over velocity extents of more than . They do not coinside with known SN remnants, fast clouds or galaxies, and their nature is unclear, although Kang and Koo (who catalogued such sources) think that these things are remnants of old SN remnants   This however does not explain the energy scale of GR emission from HESS J1503-582 (of the order of ).

(Below is the map of various FVWs within our Galaxy from Kang-Koo paper.)

Via ANKA project by S. Popov (in Russian).