A DETAILED STUDY OF NON-THERMAL X-Ray PROPERTIES AND INTERSTELLAR GAS TOWARD THE Γ-Ray SUPERNOVA REMNANT RX J1713.7–3946

Abstract

We have carried out a spectral analysis of the Suzaku X-ray data in the 0.4-12 keV range toward the shell-type very-high-energy γ-ray supernova remnant RX J1713.7−3946. The aims of this analysis are to estimate detailed X-rays spectral properties at a high angular resolution up to 2 arcmin, and to compare them with the interstellar gas. The X-ray spectrum is non-thermal and used to calculate absorbing column density, photon index, and absorption-corrected X-ray flux. The photon index varies significantly from 2.1 to 2.9. It is shown that the X-ray intensity is well correlated with the photon index, especially in the west region, with a correlation coefficient of 0.81. The X-ray intensity tends to increase with the averaged interstellar gas density while the dispersion is relatively large. The hardest spectra having the photon index less than 2.4 are found outside of the central 10 arcmin of the SNR, from the north to the southeast (∼430 arcmin 2 ) and from the southwest to the northwest (∼150 arcmin 2 ). The former region shows low interstellar gas density, while the latter high interstellar gas density. We present discussion for possible scenarios which explain the distribution of the photon index and its relationship with the interstellar gas. Subject headings: cosmic rays -ISM: clouds -ISM: individual objects (RX J1713.7−3946) -ISM: supernova remnants -X-rays: ISM

Evidence for Thermal X-Ray Line Emission From the Synchrotron-Dominated Supernova Remnant Rx J1713.7-3946

“…We can see a clear spatial variation: the interior faint region is softer than the surrounding bright shell region. This contrast is likely caused by variations of the interstellar absorption, given that the soft re-gion corresponds to a visual extinction hole (Sano et al 2015). The soft central region is an ideal location for searching for thermal X-ray emission, because (1) less absorption tends to enhance thermal X-rays which are usually softer than synchrotron X-rays, and (2) the synchrotron X-ray emission is weaker in the interior than in the surrounding shell, making it easier to detect faint thermal line emission in the presence of the dominant synchrotron continuum.…”

“…As a matter of fact, the origin of gamma rays (leptonic or hadronic) in several SNRs including RX J1713.7-3946, has been a matter of considerable debate (e.g., Aharonian et al 2004;Uchiyama et al 2007;Drury et al 2009;Abdo et al 2011;Ellison et al 2012;Fukui et al 2012;Lee et al 2012;Inoue et al 2012;Gabici & Aharonian 2014;Acero et al 2015a). Slane et al (1999) analyzed ASCA data, and estimated the upper limit of the ambient density to be 0.03-0.69 D −0.5 1 cm −3 , where D 1 is the distance in units of 1 kpc; the distance of the SNR is well established to be 1 kpc by the radial velocity of the interacting molecular gas (Fukui et al 2003), which was subsequently confirmed by Moriguchi et al (2005) and Sano et al (2010Sano et al ( , 2013Sano et al ( , 2015 from more detailed CO and X-ray studies. The loose density constraint is mainly due to the unknown plasma temperature, for which Slane et al (1999) assumed a range of 0.1-2.5 keV, which would be reasonable given the complicated electron heating mechanism at collisionless shocks (e.g., Ghavamian et al 2007;Drury et al 2009).…”

Analysis of GeV-bandγ-ray emission from supernova remnant RX J1713.7-3946

“…In an analytic assessment and detailed calculations we explore the viability of a hadronic-emission scenario involving radiation from the vicinity of RX J1713.7-3946. One-zone models of the broadband SED from X-ray (Tanaka et al 2008) to GeV γ-ray (Fermi-LAT), and TeV γ-ray (HESS) energies invariably wash over, e.g., the variations in the X-ray spectrum across the remnant (Sano et al 2015), which may reflect electron aging and a changing magnetic field (Rettig & Pohl 2012;Ressler et al 2014). A few general insights can be gained, though.…”

Prospects for Cherenkov Telescope Array Observations of the Young Supernova Remnant RX J1713.7−3946

“…(1) Hadronic model based on MHD simulations: The shock interaction with dense clouds excites turbulence, which amplifies the magnetic field up to the mG order (Inoue et al 2012;Sano et al 2013Sano et al , 2015. These results may be crucial for our better understanding of the gamma-ray and X-ray images of SNRs.…”

“…Although weak thermal X-ray emission has recently been detected from the SNR interior (Katsuda et al 2015), the X-ray emission is still dominated by synchrotron radiation, which links directly to the existence of high-energy electrons. Radio observations of CO and H I gas have revealed a highly inhomogeneous medium surrounding the SNR, such as clumpy molecular clouds (Fukui et al 2003Fukui 2013;Moriguchi et al 2005;Sano et al 2010Sano et al , 2013Sano et al , 2015. Another radio observation of CS also confirmed the existence of a very dense (>10 5 cm −3 ) ISM core toward the SNR (Maxted et al 2012).…”