Ilana Muriel Harrus

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

We report the results of spectral and morphological studies of X-ray data from the supernova remnant (SNR) W44. Spectral analysis of archival data from the Einstein Observatory, ROSAT, and Ginga, covering a total energy range from 0.3 to 8 keV, indicates that the SNR can be described well by a nonequilibrium ionization (NEI) model with temperature ~0.9 keV and ionization timescale of order 6000 cm-3 yr. All elemental abundances are found to be within about a factor of 2 of their cosmic values, with iron possibly appearing to show significant depletion. No clear evidence for emission from supernova ejecta can be inferred from the observed metal abundances. The column density toward the SNR is high—around 1022 atoms cm-2—as expected given the location of the remnant in the Galactic plane. In addition to the spectral analysis, we have investigated two different evolutionary scenarios to explain the centrally brightened X-ray morphology of the remnant: (1) a model involving the slow thermal evaporation of clouds engulfed by the 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 reproduce approximately the morphology of the SNR. The mean temperature of the hot plasma in W44 as determined by our NEI X-ray analysis provides the essential key to discriminating 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 White & Long model gives an age for the SNR of merely 6500 yr. We argue that because this age is inconsistent with the characteristic age (P/2~20,000 yr) of PSR 1853+01, the radio pulsar believed to be associated with W44, this model does not provide the explanation for the center-filled morphology. We favor the radiative-phase shock model since it can reproduce both the morphology and the age of W44, assuming reasonable values for the initial explosion energy, in the range 0.7-0.9 × 1051 ergs, and an ambient ISM density of between 3 and 4 cm-3.

Discovery of an X-Ray Synchrotron Nebula Associated with the Radio Pulsar PSR B1853+01 in the Supernova Remnant W44

We report the detection using ASCA data of a hard X-ray source in the vicinity of the radio pulsar PSR B1853+01 which is located within the supernova remnant (SNR) W44. PSR B1853+01, a 267ms pulsar, has to date only been detected in the radio band. Previous observations at soft X-ray energies (e.g., with ROSAT HRI) have failed to detect any significant X-ray emission (pulsed or unpulsed) from the pulsar. Over the 0.5--4.0keV band, the ASCA data show soft thermal emission from W44 with a morphology very similar to that observed earlier by Einstein and ROSAT. In the high energy band (4.0--9.5 keV), the SNR is, for the most part, invisible, although a source coincident with the position of PSR B1853+01 is evident. The observed ASCA spectra, extracted from a region around the PSR position, are consistent with a power-law origin (photon index =~2.3) for the X-ray emission from this source at a flux level (flux density ~~0.5 10^-6 Jy at 1 keV) consistent with previous upper limits. Timing analysis of the hard X-ray source failed to detect pulsations at the pulsars period. We conclude that the new hard source in W44 represents an X-ray synchrotron nebula associated with PSR B1853+01.

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 net = 6 (4, 9) × 1010 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 they are not well constrained by the data. Various estimates give a remnant age of order 103 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 Γ ~ 4 power law or a kT ~ 0.4 keV blackbody. The spectrum is absorbed by a H column density NH ~ 4 × 1022 cm-2 similar to that required for the remnant shell. The implied 2-9.5 keV source luminosity is about 1033 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.

A Chandra Observation of the Nearby Sculptor Group Sd Galaxy NGC?7793

We conducted a Chandra ACIS observation of the nearby Sculptor Group Sd galaxy NGC?7793 as part of a multiwavelength study of supernova remnants (SNRs) in nearby galaxies. At the assumed distance to NGC?7793 of 3.91?Mpc, the limiting unabsorbed luminosity of the detected discrete X-ray sources is L X (0.2-10.0?keV) 3?1036?erg?s?1. A total of 22 discrete sources were detected at the ~3? level or greater including one ultraluminous X-ray source (ULX). Based on multiwavelength comparisons, we identify X-ray sources coincident with one SNR, the candidate microquasar N7793-S26, one H II region, and two foreground Galactic stars. We also find that the X-ray counterpart to the candidate radio SNR R3 is time variable in its X-ray emission: we therefore rule out the possibility that this source is a single SNR. A marked asymmetry is seen in the distribution of the discrete sources with the majority lying in the eastern half of this galaxy. All of the sources were analyzed using quantiles to estimate spectral properties and spectra of the four brightest sources (including the ULX) were extracted and analyzed. We searched for time variability in the X-ray emission of the detected discrete sources using our measured fluxes along with fluxes measured from prior Einstein and R?ntgensatellit observations. From this study, three discrete X-ray sources are established to be significantly variable. A spectral analysis of the galaxys diffuse emission is characterized by a temperature of kT = 0.19-0.25?keV. The luminosity function of the discrete sources shows a slope with an absolute value of ? = ?0.65 ? 0.11 if we exclude the ULX. If the ULX is included, the luminosity function has a long tail to high L X with a poor-fitting slope of ? = ?0.62 ? 0.2. The ULX-less slope is comparable to the slopes measured for the distributions of NGC?6946 and NGC?2403 but much shallower than the slopes measured for the distributions of IC 5332 and M83. Lastly, we comment on the multiwavelength properties of the SNR population of NGC?7793.

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

ABSTRACT.The Optical Monitor Catalog 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 or 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 the 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.

Astro-H Data Analysis, Processing and Archive

Astro-H (Hitomi) is an X-ray/Gamma-ray mission led by Japan with international participation, launched on February 17, 2016. The payload consists of four different instruments (SXS, SXI, HXI and SGD) that operate simultaneously to cover the energy range from 0.3 keV up to 600 keV. This paper presents the analysis software and the data processing pipeline created to calibrate and analyze the Hitomi science data along with the plan for the archive and user support. These activities have been a collaborative effort shared between scientists and software engineers working in several institutes in Japan and USA.

An X-Ray Study of the Supernova Remnant G18.95–1.1

We present an analysis of data from both the Rontgen Satellite (ROSAT) and the Advanced Satellite for Cosmology and Astrophysics (ASCA) of the supernova remnant G18.95-1.1. We find that the X-ray emission from G18.95-1.1 is predominantly thermal, heavily absorbed with a column density around 1022 atoms cm-2, and can be best described by an nonequilibrium ionization (NEI) model with a temperature around 0.9 keV and an ionization timescale of 1.1 × 1010 cm-3 s-1. We find only marginal evidence for nonsolar abundances. Comparisons between 21 cm H I absorption data and derived parameters from our spectral analysis strongly suggest a relatively nearby remnant (a distance of about 2 kpc). Above 4 keV, we identify a small region of emission located at the tip of the central, flat-spectrum barlike feature in the radio image. We examine two possibilities for this emission region: a temperature variation within the remnant or a pulsar wind nebula (PWN). The current data do not allow us to distinguish between these possible explanations. In the scenario where this high-energy emission region corresponds to a PWN, our analysis suggests a rotational loss rate for the unseen pulsar of about 7 × 1035 ergs s-1 and a ratio Lr/LX of about 3.6 for the entire PWN, slightly above the maximum ratio (3.4 for Vela) measured in known PWNe.

Searching for the Pulsar in G18.95-1.1: Discovery of an X-ray Point Source and Associated Synchrotron Nebula with Chandra

Using the Chandra X-ray Observatory, we have pinpointed the location of a faint X-ray point source (CXOU?J182913.1-125113) and an associated diffuse nebula in the composite supernova remnant (SNR) G18.95-1.1. These objects appear to be the long-sought pulsar and its wind nebula. The X-ray spectrum of the point source is best described by an absorbed power-law model with ? = 1.6 and an NH of ~1 ? 1022?cm?2. This model predicts a relatively low unabsorbed X-ray luminosity of about LX (0.5-8.0 keV) 4.1 ? 1031?D 2 2?erg s?1, where D 2 is the distance in units of 2?kpc. The best-fit model of the diffuse nebula is a combination of thermal (kT = 0.48?keV) and non-thermal (1.4 ? ? ? 1.9) emission. The unabsorbed X-ray luminosity of LX 5.4 ? 1033?D 2 2?erg?s?1 in the 0.5-8?keV energy band seems to be largely dominated by the thermal component from the SNR, providing 87% of LX in this band. No radio or X-ray pulsations have been reported for CXOU?J182913.1-125113. If we assume an age of ~5300?yr for G18.95-1.1 and use the X-ray luminosity for the pulsar and the wind nebula together with the relationship between spin-down luminosity (via magnetic dipole radiation) and period, we estimate the pulsars period to be P 0.4?s. Compared to other rotation-powered pulsars, a magnetic field of 2.2 ? 1013?G is implied by its location in the P- diagram, a value which is close to that of the quantum critical field.