Moderately extended sources with IBIS/ISGRI

Detection of supernova remnant RX J1713.7-3946


The IBIS coded-mask telescope cannot build images of sources more extended than its angular resolution (12 arcmin). Nevertheless, if a source is slightly extended than the instrumental PSF, it is possible to extract some limited information about the spatial structure of the source [1,2,3]. Generaly, extended sources in the INTEGRAL survey are significantly smaller than systematic noise. That is why extended sources should not be significantly affected by Wavelet cleaning. To demonstrate that, we show in figure below sky images of the supernova remnant RX J1713.7-3946, which hard X-ray emission was firstly detected in [4]. The source demonstrates extended structure spatially coincided with expanding shell of supernova remnant, firstly detected in soft X-rays with ROSAT [5], in TeV energies with CANGAROO [6] and later with HESS [7,8,9].

Capture INTEGRAL/IBIS hard X-ray (17-60 keV) image of the supernova remnant RX J1713.7-3946. The total exposure time of both top images is about 20 Ms. The green contours represent surface brightness distribution measured with ROSAT in the soft X-ray (0.5-2.5 keV) band. The green crosses denote sources in the region: (1) SAX J1712.6-3739, (2) 1RXS J170849.0-400910, (3) 4U 1708-40. The yellow "X" points mark local excesses which were attributed to the systematic noise.
The deep hard X-ray sky image of the RX J1713.7-3946 obtained with general method is shown on the left. The total exposure for this region is about 20 Ms. The significance of the hard X-ray detection with IBIS/ISGRI varies along the extended structure between 6σ and 7σ. The sky image produced Wavelet cleaning method on the same data set is shown on the right. As seen from the image, the local background large-scale excess was supressed, while the spatial structure of the supernova remnant was left unchanged. However, the background correction led to the somewhat decrease of the source detection significance (5-6σ along the extended structure).
We checked stability of the apparent spatial feature by dropping observations inside 3 and 5 degrees radius around the Galactic center which is 12 degrees away from the supernova remnant. The corresponding images are shown below bottom left and right. The extended structure of interest is clearly present in sky images and looks stable against the variable noise. We also noticed supression of strong point-like artifacts (marked with yellow "X" points) in the region, which we associated with systematic noise from Galactic Center region.

References
INTEGRAL/IBIS 7-year All-Sky Hard X-Ray Survey. Part I: Image Reconstruction, accepted in Astronomy and Astrophysics, arXiv:1006.2463 [1] Renaud, M., Gros, A., Lebrun, F., Terrier, R., Goldwurm, A., Reynolds, S., & Kalemci, E. 2006a, A&A, 456, 389 [2] Renaud, M., Belanger, G., Paul, J., Lebrun, F., & Terrier, R. 2006b, A&A, 453, L5 [3] Eckert, D., Produit, N., Paltani, S., Neronov, A., & Courvoisier, T.~J.-L. 2008, A&A, 479, 27 [4] Krivonos, R., Revnivtsev, M., Lutovinov, A., Sazonov, S., Churazov, E., & Sunyaev, R. 2007, A&A, 475, 775 [5] Pfeffermann, E., & Aschenbach, B. 1996, Roentgenstrahlung from the Universe, 267 [6] Muraishi, H., et al. 2000, A&A, 354, L57 [7] Aharonian, F.~A., et al. 2004, \nat, 432, 75 [8] Aharonian, F., et al. 2006, A&A, 449, 223 [9] Aharonian, F., et al. 2007, A&A, 464, 235

Web links
INTEGRAL Picture of the Month April 2008 H.E.S.S. Collaboration: The Supernova Remnant RX J1713.7-3946 - High energy particle acceleration in the shell of a supernova remnant

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