OMCat: Catalogue of Serendipitous Sources Detected with the XMM-Newton Optical Monitor

The Optical Monitor Catalogue of serendipitous sources (OMCat) contains entries for every source detected in the publicly available XMM-Newton Optical Monitor (OM) images taken in either the imaging or ``fast'' modes. Since the OM is coaligned and records data simultaneously with the X-ray telescopes on XMM-Newton, it typically produces images in one or more near-UV/optical bands for every pointing of the observatory. As of the beginning of 2006, the public archive had covered roughly 0.5% of the sky in 2950 fields. The OMCat is not dominated by sources previously undetected at other wavelengths; the bulk of objects have optical counterparts. However, the OMCat can be used to extend optical or X-ray spectral energy distributions for known objects into the ultraviolet, to study at higher angular resolution objects detected with GALEX, or to find high-Galactic-latitude objects of interest for UV spectroscopy.Comment: 25 pages, 22 figures, submitted to PAS

Interpretation of the Center-Filled Emission from the Supernova Remnant W44

(Abridged) We have investigated two evolutionary scenarios advanced to explain the centrally-brightened X-ray morphology of the supernova remnant (SNR) W44: (1) a model involving the slow thermal evaporation of clouds engulfed by a supernova blast wave as it propagates though a clumpy interstellar medium (ISM), and (2) a hydrodynamical simulation of a blast wave propagating through a homogeneous ISM, including the effects of radiative cooling. Both models can have their respective parameters tuned to approximate the remnant's morphology. The mean temperature of the hot plasma in W44 (~0.9 keV) as determined by our nonequilibrium ionization X-ray spectral analysis provides the essential key to discriminate between these scenarios. Based on the size (using the well established distance of 3 kpc) and temperature of W44, the dynamical evolution predicted by the cloud evaporation model gives an age for the SNR of merely 6500 yr. We argue that, because this age is inconsistent with the characteristic age (approx. 20000 yr) of the associated PSR 1853+01, this model cannot provide the explanation for the center-filled morphology. We favor the radiative-phase shock model since it can reproduce both the morphology and age of W44 assuming reasonable values for the initial explosion energy in the range 0.7E51 to 0.9E51 ergs and the ambient ISM density of between 3 and 4 cm**-3.Comment: 31 pages, including 4 postscript figs, LaTeX, accepted by Ap.

HST/ACS Narrowband Imaging of the Kepler Supernova Remnant

We present narrowband images of the Kepler supernova remnant obtained with the Advanced Camera for Surveys aboard the Hubble Space Telescope. The images, with an angular resolution of 0.05" reveal the structure of the emitting gas in unprecedented detail. Radiative and nonradiative shocks are found in close proximity, unresolvable in gro~md-based spectra, indicating that the pre-shock medium is highly clumped. The ionization structure, traced by differences in the [0 111] to [N 11] flux ratio, varies on subarcsecond scales. The variation is due to 110th differences in shock velocity as well as gradients in the evolutionary stage of the shocks. A pro~llinent complex of knots protruding beyond the boundary of the ren~nallt in the northwest is found to consist of bright radiative knots, collected by arcuate nonradiative filaments. Based on the coincidence of the optical emission with a bright isolated knot of X-ray emission, we infer that this feature is due to a Rayleigh-Taylor finger that formed at the contact discontinuity and overtook the primary blast wave

A Suzaku Observation of the Low-Ionization Fe-Line Emission from RCW 86

The newly operational X-ray satellite Suzaku observed the southwestern quadrant of the supernova remnant (SNR) RCW 86 in February 2006 to study the nature of the 6.4 keV emission line first detected with the Advanced Satellite for Cosmology and Astronomy (ASCA). The new data confirm the existence of the line, localizing it for the first time; most of the line emission is adjacent and interior to the forward shock and not at the locus of the continuum hard emission. We also report the first detection of a 7.1 keV line that we interpret as the K-beta emission from low-ionization iron. The Fe-K line features are consistent with a non-equilibrium plasma of Fe-rich ejecta with n_{e}t <~ 10^9 cm^-3 s and kT_{e} ~ 5 keV. This combination of low n_{e}t and high kT_{e} suggests collisionless electron heating in an SNR shock. The Fe K-alpha line shows evidence for intrinsic broadening, with a width of 47 (34--59) eV (99% error region). The difference of the spatial distributions of the hard continuum above 3 keV and the Fe-K line emission support a synchrotron origin for the hard continuum.Comment: 6 pages with 6 figures. Accepted for PASJ Suzaku Special Issue (vo. 58, sp.1

A New Young Galactic Supernova Remnant Containing a Compact Object: G15.9+0.2

We identify the radio-emitting shell-type supernova remnant G15.9+0.2 as a relatively young remnant containing an X-ray point source that may be its associated neutron star. The integrated spectrum of the remnant shell obtained from our 30 ks exploratory Chandra observation shows very strong lines that require elevated element abundances from ejecta, in particular of sulfur. A plane-shock model fit gives a temperature $kT = 0.9 (0.8, 1.0)$ keV, an ionization timescale $n_et = 6 (4, 9) \times 10^{10}$ cm$^{-3}$ s, and a sulfur abundance of 2.1 (1.7, 2.7) times solar (90% confidence limits). Two-component models with one solar and one enriched component are also plausible, but are not well constrained by the data. Various estimates give a remnant age of order $10^3$ yr, which would make G15.9+0.2 among the dozen or so youngest remnants in the Galaxy. The sparse point source spectrum is consistent with either a steep $\Gamma \sim$ 4 power law or a $kT \sim$ 0.4 keV blackbody. The spectrum is absorbed by a H column density $N_H \sim 4 \times 10^{22}$ cm$^{-2}$ similar to that required for the remnant shell. The implied 2--9.5 keV source luminosity is about $10^{33}$ ergs s$^{-1}$ for an assumed distance of 8.5 kpc consistent with the high absorption column. We suggest that the point source is either a rotation-powered pulsar or a compact central object (CCO)

Study of the Composite Supernova Remnant MSH 11-62

We present the analysis of the X-ray data collected during an observation of the supernova remnant (SNR) MSH 11-62 by the Advanced Satellite for Cosmology and Astrophysics (ASCA). We show that MSH 11-62 is a composite remnant whose X-ray emission comes from two distinct contributions. Nonthermal, synchrotron emission, localized to a region of radius (~~)3' (consistent with a point source) dominates the total flux above 2 keV. A second contribution comes from a thermal component, extended up to a radius of (~~)6' and detected only at energies below 2keV. The spatial and spectral analysis imply the presence of a neutron star losing energy at a rate of about (10**36 - 10**37) ergs/s. No pulsed emission is detected and we set a limit on the pulsed fraction of 10%. This is consistent with the lack of a radio pulsar in the remnant, which may indicate that the pulsed emission from the rapidly rotating compact object that should be powering the synchrotron nebula is beamed and our viewing direction is unfavorable. In either event, the central neutron star deposits much of its spin-down energy into the surrounding synchrotron nebula where, through direct imaging with broadband satellites such as ASCA, it is possible to study the energetics and evolution of the compact remnant.Comment: 30 pages, including 5 figures, Latex. To appear in ApJ (May 20, 1998 issue, Vol. 499.

The Youngest Galactic Supernova Remnant: G1.9+0.3

Our 50 ks Chandra observation of the small radio supernova remnant (SNR) G1.9+0.3 shows a complete shell structure with strong bilateral symmetry, about $100''$ in diameter. The radio morphology is also shell-like, but only about $84''$ in diameter, based on observations made in 1985. We attribute the size difference to expansion between 1985 and our Chandra observations of 2007. Expansion is confirmed in comparing radio images from 1985 and 2008. We deduce that G1.9+0.3 is of order 100 years old -- the youngest supernova remnant in the Galaxy. Based on a very high absorbing column density of $5.5 \times 10^{22}$ cm$^{-2}$, we place G1.9+0.3 near the Galactic Center, at a distance of about 8.5 kpc, where the mean remnant radius would be about 2 pc, and the required expansion speed about $14,000$ km s$^{-1}$. The X-ray spectrum is featureless and well-described by the exponentially cut off synchrotron model {\tt srcut}. With the radio flux at 1 GHz fixed at 0.9 Jy, we find a spectral index of 0.65 and a rolloff frequency of $1.4 \times 10^{18}$ Hz. The implied characteristic rolloff electron energy of about $94 (B/10 \mu{\rm G})^{-1/2}$ TeV is the highest ever reported for a shell supernova remnant. It can easily be reached by standard diffusive shock acceleration, given the very high shock velocities; it can be well described by either age-limited or synchrotron-loss-limited acceleration. Not only is G1.9+0.3 the youngest known Galactic remnant, it is also only the fourth Galactic X-ray synchrotron-dominated shell supernova remnant.Comment: 4 pages, 5 figures; revised to include new radio data and accepted for ApJ

A New ASCA and ROSAT Study of the Supernova Remnant: G272.2-3.2

G272.2-3.2 is a supernova remnant (SNR) characterized by an apparent centrally brightened X-ray morphology and thermally dominated X-ray emission. Because of this combination of Sedov-type (thermal emission) and non-Sedov type (non-shell like morphology) features, the remnant is classified as a ``thermal composite'' SNR. This class of remnant is still poorly understood due in part to the difficulties in modeling accurately all the physical conditions which shape the emission morphology. In this paper we present a combined analysis of data from the ASCA and ROSAT satellites coupled with previous results at other wavelengths. We find that the X-ray emission from G272.2-3.2 is best described by a non-equilibrium ionization (NEI) model with a temperature around 0.70 keV, an ionization timescale of 3200 cm^-3 yr and a relatively high column density (NH about 10^22 atoms/cm^2). We look into the possible explanations for the apparent morphology of G272.2-3.2 using several models (among which both cloud evaporation and thermal conduction models). For each of the models considered we examine all the implications on the evolution of G272.2-3.2.Comment: 26 pages, 8 figures. Accepted for publication in Ap

A Suzaku Observation of the Neutral Fe-line Emission from RCW 86

The newly operational X-ray satellite Suzaku observed the supernova remnant (SNR) RCW 86 in February 2006 to study the nature of the 6.4 keV emission line first detected with the Advanced Satellite for Cosmology and Astronomy (ASCA). The new data confirms the existence of the line, localizing it for the first time inside a low temperature emission region and not at the locus of the continuum hard X-ray emission. We also report the first detection of a 7.1 keV line that we interpret as the K(beta) emission from neutral or low-ionized iron. The Fe-K line features are consistent with a non-equilibrium plasma of Fe-rich ejecta with n(sub e) less than or approx. equal to 10(exp 9)/cu cm s and kT(sub e) > 1 keV. We found a sign that Fe K(alpha) line is intrinsically broadened 47 (35-57) eV (99% error region). Cr-K line is also marginally detected, which is supporting the ejecta origin for the Fe-K line. By showing that the hard continuum above 3 keV has different spatial distribution from the Fe-K line, we confirmed it to be synchrotron X-ray emission