We present X-ray proper-motion measurements of the forward shock and reverse-shocked ejecta in Tycho's supernova remnant, based on three sets of archival Chandra data taken in 2000, 2003, and 2007. We find that the proper motion of the edge of the remnant (i.e., the forward shock and protruding ejecta knots) varies from 0 ′′ .20 yr −1 (expansion index m = 0.33, where R = t m ) to 0 ′′ .40 yr −1 (m = 0.65) with azimuthal angle in 2000-2007 measurements, and 0 ′′ .14 yr −1 (m = 0.26) to 0 ′′ .40 yr −1 (m = 0.65) in 2003-2007 measurements. The azimuthal variation of the proper motion and the average expansion index of ∼0.5 are consistent with those derived from radio observations. We also find proper motion and expansion index of the reverse-shocked ejecta to be 0 ′′ .21-0 ′′ .31 yr −1 and 0.43-0.64, respectively. From a comparison of the measured m-value with Type Ia supernova evolutionary models, we find a pre-shock ambient density around the remnant of 0.2 cm −3 .

We show that the expansion of ejecta in Tycho's supernova remnant (SNR) is consistent with a spherically symmetric shell, based on Suzaku measurements of the Doppler broadened X-ray emission lines. All the strong Kα line emission show broader widths at the center than at the rim, while the centroid energies are constant across the remnant (except for Ca). This is the pattern expected for Doppler broadening due to expansion of the SNR ejecta in a spherical shell. To determine the expansion velocities of the ejecta, we applied a model for each emission line feature having two Gaussian components separately representing red-and blue-shifted gas, and inferred the Doppler velocity difference between these two components directly from the fitted centroid energy difference. Taking into account the effect of projecting a three-dimensional shell to the plane of the detector, we derived average spherical expansion velocities independently

While X-ray spectroscopy, timing, and imaging have improved much since 1962 when the first astronomical nonsolar source was discovered, especially wi the launch of the Newton/X-ray Multi-Mirror Mission, Rossi/X-ray Timing Explorer, and Chandra/Advanced X-ray Astrophysics Facility, the progress of X-ray polarimetry has been meager. This is in part due to the lack of sensitive polarization detectors, which in turn is a result of the fate of approved missions and because celestial X-ray sources appear less polarized than expected. Only one positive measurement has been available until now: the Orbiting Solar Observatory measured the polarization of the Crab Nebula in the 1970s. The advent of microelectronics techniques has allowed for designing a detector based on the photoelectric effect of gas in an energy range where the optics are efficient at focusing in X-rays. Here we describe the instrument, which is the major contribution of the Italian collaboration to the Small Explorer mission called IXPE, the Imaging X-ray Polarimetry Explorer, which will launch in late 2021. The instrument is composed of three detector units based on this technique and a detector service unit. Three mirror modules provided by Marshall Space Flight Center focus X-rays onto the detectors. We show the technological choices, their scientific motivation, and results from the calibration of the instrument. IXPE will perform imaging, timing, and energy-resolved polarimetry in the 2–8 keV energy band opening this window of X-ray astronomy to tens of celestial sources of almost all classes.

Tycho's supernova remnant was observed by the XIS and HXD instruments onboard the Suzaku satellite on 2006 June 26-29 for 92 ks. The spectrum up to 30 keV was well fitted with a two-component model, consisting of a power-law with photon index of 2.7 and a thermal bremsstrahlung model with temperature of 4.7 keV. The former component can alternatively be modeled as synchrotron emission from a population of relativistic electrons with an estimated roll-off energy of around 1 keV. In the XIS spectra, in addition to the prominent Fe K α line (6.445 keV), we observe 1 for the first time significant K α line emission from the trace species Cr and Mn at energies of 5.48 keV and 5.95 keV, respectively. Faint K β lines from Ca (4.56 keV) and Fe (7.11 keV) are also seen. The ionization states of Cr and Mn, based on their line centroids, are estimated to be similar to that of Fe K α (Fe XV or XVI).

A Suzaku observation of a giant radio galaxy, 3C 326, which has a physical size of about 2 Mpc, was conducted on 2008 January 19-21. In addition to several X-ray sources, diffuse emission was significantly detected and associated with its west lobe, but the east lobe was contaminated by an unidentified X-ray source WARP J1552.4+2007. After careful evaluation of the X-ray and non-X-ray background, the 0.4-7 keV X-ray spectrum of the west lobe is described by a power-law model modified with the Galactic absorption. The photon index and 1 keV flux density were derived as Γ = 1.82 +0.26 −0.24 ± 0.04 and S X = 19.4 +3.3 −3.2 ± 3.0 nJy, respectively, where the first and second errors represent the statistical and systematic ones. The diffuse X-rays were attributed to be inverse Compton (IC) radiation by the synchrotron radio electrons scattering off the cosmic microwave background photons. This radio galaxy is the largest among those with lobes detected through IC X-ray emission. A comparison of the radio to X-ray fluxes yields the energy densities of electron and magnetic field as u e = (2.3 ± 0.3 ± 0.3) × 10 −13 erg cmand u m = (1.2 +0.2 −0.1 ± 0.2) × 10 −14 erg cm −3 , respectively. The galaxy is suggested to host a low-luminosity nucleus with an absorption-corrected 2-10 keV luminosity of < 2 × 10 42 erg s −1 , together with a relatively weak radio core. The energetics in the west lobe of 3C 326 were compared with those of moderate radio galaxies with a size of ∼100 kpc. The west lobe of 3C 326 is confirmed to agree with the correlations for the moderate radio galaxies, u e ∝ D −2.2±0.4 and u m ∝ D −2.4±0.4 , where D is their total physical size. This implies that the lobes of 3C 326 are still being energized by the jet, despite the current weakness of the nuclear activity.