A Major X-Ray Outburst From an Ultraluminous X-Ray Source in M82
Abstract
We detected a major X-ray outburst from M82 with a duration of 79 days, an average flux of 5 × 10-11 erg cm-2 s-1 in the 2-10 keV band, and strong variability. The X-ray spectrum remained hard throughout the outburst. We obtained a Chandra observation during the outburst that shows that the emission arises from the ultraluminous X-ray source X41.4+60. This source has an unabsorbed flux of (5.4 ± 0.2) × 10-11 erg cm-2 s-1 in the 0.3-8 keV band, equivalent to an isotropic luminosity of 8.5 × 1040 erg s-1. The spectrum is adequately fitted with an absorbed power law with a photon index of 1.55 ± 0.05. This photon index is very similar to the value of 1.61 ± 0.06 measured previously while the flux was (2.64 ± 0.14) × 10-11 erg cm-2 s-1. Thus, the source appears to remain in the hard state even at the highest flux levels observed. The X-ray spectral and timing data available for X41.4+60 are consistent with the source being in a luminous hard state and a black hole mass in the range of one to a few thousand solar masses.
- Publication:
-
The Astrophysical Journal
- Pub Date:
- February 2009
- DOI:
- 10.1088/0004-637X/692/1/653
- arXiv:
- arXiv:0810.5134
- Bibcode:
- 2009ApJ...692..653K
- Keywords:
-
- black hole physics;
- galaxies: individual: M82;
- galaxies: stellar content;
- X-rays: binaries;
- X-rays: galaxies;
- Astrophysics
- E-Print:
- to appear in ApJ, 7 pages