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Register a new userX-ray Proper Motions and Shock Speeds along the Northwest Rim of SN 1006
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We report the results of an X-ray proper motion measurement for the NW rim of SN1006, carried out by comparing Chandra observations from 2001 and 2012. The NW limb has predominantly thermal X-ray emission, and it is the only location in SN1006 with significant optical emission: a thin, Balmer-dominated filament. For most of the NW rim, the proper motion is about 0.30 arcsec/yr, essentially the same as has been measured from the H-alpha filament. Isolated regions of the NW limb are dominated by nonthermal emission, and here the proper motion is much higher, 0.49 arcsec/yr, close to the value measured in X-rays along the much brighter NE limb, where the X-rays are overwhelmingly nonthermal. At the 2.2 kpc distance to SN1006, the proper motions imply shock velocities of about 3000 km/s and 5000 km/s in the thermal and nonthermal regions, respectively. A lower velocity behind the H-alpha filament is consistent with the picture that SN1006 is encountering denser gas in the NW, as is also suggested by its overall morphology. In the thermally-dominated portion of the X-ray shell, we also see an offset in the radial profiles at different energies; the 0.5-0.6 keV peak dominated by O VII is closer to the shock front than that of the 0.8-3 keV emission--due to the longer times for heavier elements to reach ionization states where they produce strong X-ray emission.
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The Schweizer-Middleditch star, located behind the SN 1006 remnant and near its center in projection, provides the opportunity to study cold, expanding ejecta within the SN 1006 shell through UV absorption. Especially notable is an extremely sharp red edge to the Si II 1260 Angstrom feature, which stems from the fastest moving ejecta on the far side of the SN 1006 shell--material that is just encountering the reverse shock. Comparing HST far-UV spectra obtained with COS in 2010 and with STIS in 1999, we have measured the change in this feature over the intervening 10.5-year baseline. We find that the sharp red edge of the Si II feature has shifted blueward by 0.19 +/- 0.05 Angstroms, which means that the material hitting the reverse shock in 2010 was moving slower by 44 +/- 11 km/s than the material that was hitting it in 1999, a change corresponding to - 4.2 +/- 1.0 km/s/yr. This is the first observational confirmation of a long-predicted dynamic effect for a reverse shock: that the shock will work its way inward through expanding supernova ejecta and encounter ever slower material as it proceeds. We also find that the column density of shocked Si II (material that has passed through the reverse shock) has decreased by 7 +/- 2% over the ten-year period. The decrease could indicate that in this direction the reverse shock has been ploughing through a dense clump of Si,leading to pressure and density transients.
We report on the first X-ray proper-motion measurements of the nonthermally-dominated forward shock in the northeastern limb of SN 1006, based on two Chandra observations taken in 2000 and 2008. We find that the proper motion of the forward shock is about 0.48 arcsec/yr and does not vary around the rim within the ~10% measurement uncertainties. The proper motion measured is consistent with that determined by the previous radio observations. The mean expansion index of the forward shock is calculated to be ~0.54 which matches the value expected based on an evolutionary model of a Type Ia supernova with either a power-law or an exponential ejecta density profile. Assuming pressure equilibrium around the periphery from the thermally-dominated northwestern rim to the nonthermally-dominated northeastern rim, we estimate the ambient density to the northeast of SN 1006 to be about 0.085/cm^3.
We report the first measurement of proper motions in the SN1006 remnant (G327.6+14.6) based entirely on digital images. CCD images from three epochs spanning a period of 11 years are used: 1987 from Las Campanas, and 1991 and 1998 from CTIO. Measuring the shift of delicate Balmer filaments along the northwest rim of the remnant, we obtain proper motions of 280 +/- 8 mas/yr along the entire length where the filaments are well defined, with little systematic variation along the filaments. We also report very deep Halpha imaging observations of the entire remnant that clearly show very faint emission surrounding almost the entire shell, as well as some diffuse emission regions in the (projected) interior. Combining the proper motion measurement with a recent measurement of the shock velocity based on spectra of the same filaments by Ghavamian et al. leads to a distance of 2.17 +/- 0.08 kpc to SN1006. Several lines of argument suggest that SN1006 was a Type Ia event, so the improved distance measurement can be combined with the peak luminosity for SNeIa, as determined for events in galaxies with Cepheid-based distances, to calculate the apparent brightness of the spectacular event that drew wide attention in the eleventh century. The result, V_max = -7.5 =/- 0.4, lies squarely in the middle of the wide range of estimates based on the historical observations.
The differential spectrum of TeV gamma rays between 1.5 TeV and 20 TeV from the north-east rim of SN1006 was obtained from the data observed in 1996 and 1997 using the 3.8m CANGAROO v{C}erenkov telescope. This spectrum matches the model calculated using the Inverse Compton (IC) process with 2.7k Cosmic Microwave Background (CMB). This enables us to estimate the absolute strength of the magnetic field around the shock and the maximum energy of accelerated electrons with the considerable accuracy: the obtained field strength and maximum electron energy are $4pm1$ $mu$G and 50 TeV respectively. Also we have detected again the TeV gamma-ray emission from the same position using the 10m CANGAROO-II telescope in 2000, and the preliminary spectrum around 1 TeV region is presented in this conference. The two spectra agree well in the overlapped energy region.
The supernova remnant SN 1006 is a source of high-energy particles and its southwestern limb is interacting with a dense ambient cloud, thus being a promising region for gamma-ray hadronic emission. We aim at describing the physics and the nonthermal emission associated with the shock-cloud interaction to derive the physical parameters of the cloud (poorly constrained by the data analysis), to ascertain the origin of the observed spatial variations in the spectral properties of the X-ray synchrotron emission, and to predict spectral and morphological features of the resulting gamma-ray emission. We performed 3-D magnetohydrodynamic simulations modeling the evolution of SN 1006 and its interaction with the ambient cloud, and explored different model setups. By applying the REMLIGHT code on the model results, we synthesized the synchrotron X-ray emission, and compared it with actual observations, to constrain the parameters of the model. We also synthesized the leptonic and hadronic gamma-ray emission from the models, deriving constraints on the energy content of the hadrons accelerated at the southwestern limb. We found that the impact of the SN 1006 shock front with a uniform cloud with density 0.5 cm^-3 can explain the observed morphology, the azimuthal variations of the cutoff frequency of the X-ray synchrotron emission, and the shock proper motion in the interaction region. Our results show that the current upper limit for the total hadronic energy in the southwestern limb is 2.5e49 erg.
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