* Astronomy

Title: Investigation of X-ray cavities in the cooling flow system Abell 1991
Authors: M.B.Pandge, N.D.Vagshette, S.S.Sonkamble, M.K.Patil

We present results based on the systematic analysis of Chandra archive data on the X-ray bright Abell Richness class-I type cluster Abell 1991 with an objective to investigate properties of the X-ray cavities hosted by this system. The unsharp masked image as well as 2-d \beta model subtracted residual image of Abell 1991 reveals a pair of X-ray cavities and a region of excess emission in the central ~12 kpc region. Both the cavities are of ellipsoidal shape and exhibit an order of magnitude deficiency in the X-ray surface brightness compared to that in the undisturbed regions. Spectral analysis of X-ray photons extracted from the cavities lead to the temperature values equal to 1.77_{-0.12}^{+0.19} keV for N-cavity and 1.53_{-0.06}^{+0.05} keV for S-cavity, while that for the excess X-ray emission region is found to be equal to 2.06_{-0.07}^{+0.12} keV. Radial temperature profile derived for Abell 1991 reveals a positive temperature gradient, reaching to a maximum of 2.63 keV at ~ 76 kpc and then declines in outward direction. 0.5-2.0 keV soft band image of the central 15" region of Abell 1991 reveals relatively cooler three different knot like features that are about 10" off the X-ray peak of the cluster. Total power of the cavities is found to be equal to ~ 8.64 x 10^{43} \lum, while the X-ray luminosity within the cooling radius is found to be 6.04 x 10^{43} \lum, comparison of which imply that the mechanical energy released by the central AGN outburst is sufficient to balance the radiative loss.

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