RXTE Observation of the Nonthermal Emission from the Early Stage Merger in A1750
Abstract
We make the first observation-based calculation of the energy that goes into cosmic ray protons versus cosmic ray electrons in shock acceleration during structure formation. We find a ratio of energy in cosmic ray protons to energy in cosmic ray electrons of 0.86. This value, calculated from the nonthermal X-ray component reported here from RTXE and the Fermi LAT upper limit for gamma-ray emission, is significantly lower than theoretical estimates that place most of the nonthermal energy in protons. Our estimate is based on the detection of nonthermal X-ray emission using the 3-20 keV RXTE spectrum, which shows residual emission not well modeled by a single thermal component. The statistical significance of adding a nonthermal, power-law component is 96%. The significance of adding a second thermal component is 90%. The addition of a component consisting of full cosmic X-ray background fluctuation to an isothermal model is significant with 92% confidence. The cumulative probability for the two-thermal-component model is 81% and 90% for the thermal plus power law. Thus the model with nonthermal emission is the preferred description of the data. Evidence of shock heating between the clusters in the spectro-imaging data of XMM, Chandra, and Suzaku indicates that a cosmic ray component should also be present and supports a nonthermal interpretation for the additional component. The bolometric nonthermal X-ray luminosity is 1.6 × 1044 ergs s-1, 36% of the total X-ray emission in the 0.1-100 keV band.
- Publication:
-
The Astrophysical Journal
- Pub Date:
- July 2022
- DOI:
- 10.3847/1538-4357/ac71ac
- arXiv:
- arXiv:2207.13753
- Bibcode:
- 2022ApJ...933...34H
- Keywords:
-
- Non-thermal radiation sources;
- Galaxy clusters;
- 1119;
- 584;
- Astrophysics - High Energy Astrophysical Phenomena;
- Astrophysics - Cosmology and Nongalactic Astrophysics
- E-Print:
- ApJ, 933, 34 (2022)