Evidence for X-Ray Synchrotron Emission from Simultaneous Mid-Infrared to X-Ray Observations of a Strong Sgr A* Flare
Abstract
This paper reports measurements of Sgr A* made with NACO in L' band (3.80 μm), Ks band (2.12 μm), and H band (1.66 μm), and with VISIR in N band (11.88 μm) at the ESO VLT, as well as with XMM-Newton at X-ray (2-10 keV) wavelengths. On 2007 April 4, a very bright flare was observed from Sgr A* simultaneously at L' band and X-ray wavelengths. No emission was detected using VISIR. The resulting spectral energy distribution has a blue slope (β>0 for νL ν vprop νβ, consistent with νL ν vprop ν0.4) between 12 μm and 3.8 μm. For the first time, our high-quality data allow a detailed comparison of infrared (IR) and X-ray light curves with a resolution of a few minutes. The IR and X-ray flares are simultaneous to within 3 minutes. However, the IR flare lasts significantly longer than the X-ray flare (both before and after the X-ray peak), and prominent substructures in the 3.8 μm light curve are clearly not seen in the X-ray data. From the shortest timescale variations in the L'-band light curve, we find that the flaring region must be no more than 1.2RS in size. The high X-ray to IR flux ratio, blue νL ν slope MIR to L' band, and the soft νL ν spectral index of the X-ray flare together place strong constraints on possible flare emission mechanisms. We find that it is quantitatively difficult to explain this bright X-ray flare with inverse Compton processes. A synchrotron emission scenario from an electron distribution with a cooling break is a more viable scenario.
- Publication:
-
The Astrophysical Journal
- Pub Date:
- June 2009
- DOI:
- 10.1088/0004-637X/698/1/676
- arXiv:
- arXiv:0903.3416
- Bibcode:
- 2009ApJ...698..676D
- Keywords:
-
- accretion;
- accretion disks;
- black hole physics;
- Galaxy: center;
- infrared: general;
- radiation mechanisms: general;
- X-rays: general;
- Astrophysics - Galaxy Astrophysics;
- Astrophysics - High Energy Astrophysical Phenomena
- E-Print:
- ApJ, 49 pages, 9 figures