Localizing the VHE γ-ray source at the Galactic Centre

Abstract

The inner 10 pc of our Galaxy contains many counterpart candidates of the very high energy (VHE; >100 GeV) γ-ray point source HESS J1745−290. Within the point spread function of the H.E.S.S. measurement, at least three objects are capable of accelerating particles to VHE and beyond and of providing the observed γ-ray flux. Previous attempts to address this source confusion were hampered by the fact that the projected distances between these objects were of the order of the error circle radius of the emission centroid (34 arcsec, dominated by the pointing uncertainty of the H.E.S.S. instrument). Here we present H.E.S.S. data of the Galactic Centre region, recorded with an improved control of the instrument pointing compared to H.E.S.S. standard pointing procedures. Stars observed during γ-ray observations by optical guiding cameras mounted on each H.E.S.S. telescope are used for off-line pointing calibration, thereby decreasing the systematic pointing uncertainties from 20 to 6 arcsec per axis. The position of HESS J1745−290 is obtained by fitting a multi-Gaussian profile to the background-subtracted γ-ray count map. A spatial comparison of the best-fitting position of HESS J1745−290 with the position and morphology of candidate counterparts is performed. The position is, within a total error circle radius of 13 arcsec, coincident with the position of the supermassive black hole Sgr A* and the recently discovered pulsar wind nebula candidate G359.95−0.04. It is significantly displaced from the centroid of the supernova remnant Sgr A East, excluding this object with high probability as the dominant source of the VHE γ-ray emission

Leptonic origin of the 100 MeVγ-ray emission from the Galactic centre

“…The source of the GeV and TeV γ-rays is not variable and it is not clear if the emission comes from the vicinity of the black hole, if it is produced in an extended region around the black hole, or, finally, if it comes from an unrelated source positionally coincident with the supermassive black hole in Sgr A*. The best positional uncertainty of 6 on TeV source HESS J1745-303 (Acero et al 2010) still allows several sources to be responsible for the observed very high energy(VHE) emission: the central black hole itself (Aharonian & Neronov 2005a), a plerion within several arcseconds from the GC (Wang et al 2006;Hinton & Aharonian 2007), a putative black hole plerion around Sgr A* (Atoyan & Dermer 2004), and the central diffuse region around the GC (Aharonian & Neronov 2005b;Ballantyne et al 2007;Chernyakova et al 2011).…”

Ground- and Space-Based Gamma-Ray Astronomy

“…Detailed studies of the position of the source with the high-angular resolution of H.E.S.S. has provided the most accurate position to date (192): the source is within 8 ±9 stat ±9 sys from the position of Sgr A with an upper limit on the extension of the source of 1.3' (95% confidence level). This measurement rules out the SNR Sgr A East as a source of the gamma-ray emission, leaving two main objects as possible astrophysical counterparts: the supermassive black hole Sgr A or the pulsar wind nebula PWN G359.95-0.04 (193).…”

The inner 300 parsecs of the Milky Way seen by H.E.S.S.: a Pevatron in the Galactic Centre

“…1). The position of the HESS J1745-290 centroid is coincident with Sgr A* and the pulsar wind nebula G359.95-0.04 positions within 13 [3]. The energy spectrum of HESS J1745-290 derived from 10 year observations with H.E.S.S.…”