Hard X-ray Emission from the NGC 5044 Group
Abstract
Observations made with the Rossi X-ray Timing Explorer Proportional Counter Array (PCA) to constrain the hard X-ray emission in the NGC 5044 group are reported here. Modeling a combined PCA and ROSAT position sensitive proportional counter spectrum with a 0.5-15 keV energy range shows excess hard emission above 4 keV. Addition of a power-law component with a spectral index of 2.6-2.8 and a luminosity of 2.6 × 1042 erg s-1 within 700 kpc in the observed energy band removes these residuals. Thus, there is a detection of a significant non-thermal component that is 32% of the total X-ray emission. Point-source emission makes up at most 14% of the non-thermal emission from the NGC 5044 group. Therefore, the diffuse, point-source-subtracted, non-thermal component is (2.2-3.0) × 1042 erg s-1. The cosmic-ray electron energy density is 3.6 × 10-12 erg cm-3 and the average magnetic field is 0.034 μG in the largest radio emitting region. The ratio of cosmic-ray electron energy density to magnetic field energy density, ~2.5 × 104, is significantly out of equipartition and is therefore atypical of radio lobes. In addition, the group's small size and low non-thermal energy density strongly contradicts the size-energy relationship found for radio lobes. Thus, it is unlikely related to the active galaxy and is most likely a relic of the merger. The energy in cosmic rays and magnetic field is consistent with simulations of cosmic-ray acceleration by merger shocks.
- Publication:
-
The Astrophysical Journal
- Pub Date:
- January 2011
- DOI:
- 10.1088/0004-637X/726/1/9
- arXiv:
- arXiv:1102.0967
- Bibcode:
- 2011ApJ...726....9H
- Keywords:
-
- galaxies: clusters: individual: WP 23;
- galaxies: groups: individual: NGC 5044;
- Astrophysics - Cosmology and Nongalactic Astrophysics
- E-Print:
- 17 pages, including 4 figures and 2 tables