5 years of survey on the Crab Nebula with SPI/INTEGRAL

TL;DR

This study analyzes over five years of SPI/INTEGRAL observations of the Crab Nebula above 20 keV, revealing a stable spectral shape with a broken power law model and consistent flux over time.

Contribution

It provides a detailed, long-term spectral analysis of the Crab Nebula, demonstrating spectral curvature and flux stability using extensive observational data.

Findings

Spectral curvature is observed in the Crab Nebula's emission.

A broken power law fits the data better than a single power law.

The spectral shape and flux are stable over five years.

Abstract

We present observations of the Crab Nebula above 20 keV by the SPI/INTEGRAL telescope during more than 5 years of operations. Our study demonstrates the stability of the instrument with time and allows a detailed analysis of the emission observed from the Crab Nebula between 20 keV and 1 MeV. The flux stability is discussed and serves a robust spectral shape analysis. We find that a single power law is clearly excluded since the photon spectrum presents a curvature in the considered energy domain. We have modelled it by a broken power law with the energy break fixed to 100 keV and determined the two photon indices together with the 100 keV flux for 9 periods between 2004 and 2008. The spectral shape of the Crab nebula is very stable as well as its intensity and connects nicely with previous measurements, at lower (X-rays) or higher (MeV) energies.