Advanced CCD Imaging Spectrometer Observation Research Articles

The Massive Star-forming Regions Omnibus X-ray Catalog, Third Installment

Abstract We offer to the star formation community the third installment of the Massive Star-forming Regions (MSFRs) Omnibus X-ray Catalog (MOXC3), a compilation of X-ray point sources detected in 50 archival Chandra Advanced CCD Imaging Spectrometer observations of 14 Galactic MSFRs and surrounding fields. The MOXC3 MSFRs are NGC 2264, NGC 6193, RCW 108-IR, Aur OB1, DR15, NGC 6231, Berkeley 87, NGC 6357, AFGL 4029, h Per (NGC 869), NGC 281, Onsala 2S, G305, and RCW 49 (Wd 2); they have distances of 0.7–4.2 kpc. Most exhibit clumped or clustered young stellar populations; several contain at least two distinct massive young stellar clusters. The total MOXC3 catalog includes 27,923 X-ray point sources. We take great care to identify even the faintest X-ray point sources across these fields. This allows us to remove this point source light, revealing diffuse X-ray structures that pervade and surround MSFRs, often generated by hot plasmas from massive star feedback. As we found in MOXC1 and MOXC2, diffuse X-ray emission is traceable in all MOXC3 MSFRs; here we perform spectral fitting to investigate the origins of selected diffuse regions. Once again, MOXC3 shows the value of high spatial resolution X-ray studies of MSFRs enabled by Chandra.

The Expansion of the Forward Shock of 1E 0102.2–7219 in X-Rays

Abstract We measure the expansion of the forward shock of the Small Magellanic Cloud supernova remnant 1E 0102.2–7219 in X-rays using Chandra X-Ray Observatory on-axis Advanced CCD Imaging Spectrometer observations from 1999 to 2016. We estimate an expansion rate of 0.025% ± 0.006% yr−1 and a blast wave velocity of ( 1.61 ± 0.37 ) × 10 3 km s − 1 . Assuming partial electron–ion equilibration via Coulomb collisions and cooling due to adiabatic expansion, this velocity implies a post-shock electron temperature of 0.84 ± 0.20 keV, which is consistent with the estimate of 0.68 ± 0.05 keV based on the X-ray spectral analysis. We combine the expansion rate with the blast wave and reverse shock radii to generate a grid of one-dimensional models for a range of ejecta masses ( 2 – 6 M ☉ ) to constrain the explosion energy, age, circumstellar density, swept-up mass, and unshocked-ejecta mass. We find acceptable solutions for a constant-density ambient medium and for an r −2 power-law profile (appropriate for a constant progenitor stellar wind). For the constant-density case, we find an age of ∼1700 yr, explosion energies (0.87–2.61) × 1051 erg, ambient densities 0.85–2.54 amu cm−3, swept-up masses 22 – 66 M ☉ , and unshocked-ejecta masses 0.05 – 0.16 M ☉ . For the power-law density profile, we find an age of ∼2600 yr, explosion energies (0.34–1.02) × 1051 erg, densities 0.22 – 0.66 amu cm − 3 at the blast wave, swept-up masses 17 – 52 M ☉ , and unshocked-ejecta masses 0.06 – 0.18 M ☉ . Assuming that the true explosion energy was (0.5–1.5) × 1051 erg, ejecta masses 2 – 3.5 M ☉ are favored for the constant-density case and 3 – 6 M ☉ for the power-law case. The unshocked-ejecta mass estimates are comparable to Fe masses expected in core-collapse supernovae with progenitor mass 15.0 – 40.0 M ☉ , offering a possible explanation for the lack of Fe emission observed in X-rays.

Chandra Survey of Nearby Galaxies: The Catalog

Abstract We searched the public archive of the Chandra X-ray Observatory as of 2016 March and assembled a sample of 719 galaxies within 50 Mpc with available Advanced CCD Imaging Spectrometer observations. By cross-correlation with the optical or near-infrared nuclei of these galaxies, 314 of them are identified to have an X-ray active galactic nucleus (AGN). The majority of them are low-luminosity AGNs and are unlikely X-ray binaries based upon their spatial distribution and luminosity functions. The AGN fraction is around 60% for elliptical galaxies and early-type spirals, but drops to roughly 20% for Sc and later types, consistent with previous findings in the optical. However, the X-ray survey is more powerful in finding weak AGNs, especially from regions with active star formation that may mask the optical AGN signature. For example, 31% of the H ii nuclei are found to harbor an X-ray AGN. For most objects, a single power-law model subject to interstellar absorption is adequate to fit the spectrum, and the typical photon index is found to be around 1.8. For galaxies with a non-detection, their stacked Chandra image shows an X-ray excess with a luminosity of a few times 1037 erg s−1 on average around the nuclear region, possibly composed of faint X-ray binaries. This paper reports on the technique and results of the survey; in-depth analysis and discussion of the results will be reported in forthcoming papers.

CHANDRA ACIS SURVEY OF X-RAY POINT SOURCES: THE SOURCE CATALOG

ABSTRACT The Chandra archival data is a valuable resource for various studies on different X-ray astronomy topics. In this paper, we utilize this wealth of information and present a uniformly processed data set, which can be used to address a wide range of scientific questions. The data analysis procedures are applied to 10,029 Advanced CCD Imaging Spectrometer observations, which produces 363,530 source detections belonging to 217,828 distinct X-ray sources. This number is twice the size of the Chandra Source Catalog (Version 1.1). The catalogs in this paper provide abundant estimates of the detected X-ray source properties, including source positions, counts, colors, fluxes, luminosities, variability statistics, etc. Cross-correlation of these objects with galaxies shows that 17,828 sources are located within the D 25 isophotes of 1110 galaxies, and 7504 sources are located between the D 25 and 2D 25 isophotes of 910 galaxies. Contamination analysis with the log N–log S relation indicates that 51.3% of objects within 2D 25 isophotes are truly relevant to galaxies, and the “net” source fraction increases to 58.9%, 67.3%, and 69.1% for sources with luminosities above 1037, 1038, and 1039 erg s−1, respectively. Among the possible scientific uses of this catalog, we discuss the possibility of studying intra-observation variability, inter-observation variability, and supersoft sources (SSSs). About 17,092 detected sources above 10 counts are classified as variable in individual observation with the Kolmogorov–Smirnov (K–S) criterion (P K–S < 0.01). There are 99,647 sources observed more than once and 11,843 sources observed 10 times or more, offering us a wealth of data with which to explore the long-term variability. There are 1638 individual objects (∼2350 detections) classified as SSSs. As a quite interesting subclass, detailed studies on X-ray spectra and optical spectroscopic follow-up are needed to categorize these SSSs and pinpoint their properties. In addition, this survey can enable a wide range of statistical studies, such as X-ray activity in different types of stars, X-ray luminosity functions in different types of galaxies, and multi-wavelength identification and classification of different X-ray populations.

X-ray spectrum variations in the south-west Cygnus Loop

The Cygnus Loop is one of the nearest supernova remnants (440 pc), allowing studies of spatial variations to be carried out at high physical resolution compared with other supernova remnants. Chandra Advanced CCD Imaging Spectrometer (ACIS) observations were obtained covering the bright V-shaped region on the south-west limb. This region has strong 0.2–2 keV spectral variations seen with the ROSAT Position Sensitive Proportional Counter. The nature of the spectral variations is analysed using the ACIS observations. It is found that temperature, abundance variations and column density variations all have a significant contribution to the observed spectral variations. Fits with C, N, O (O group) elements and Ne, Na, Mg, Al, Si, S, Ar (Ne group) elements varied together are better than fits with just O and Ne varied. Large spatial variations in abundances are seen, yet the Ne group to O group ratio and the Fe group (Ca, Fe, Ni) to O group ratio are nearly constant for all of the spectra. The most natural explanation is that the elements in the region are due to supernova explosion of a star of ∼18 M⊙ which predated the Cygnus Loop explosion.

ITAL]Chandra[/ITAL] Observation of Supernova Remnant G54.1+0.3: A Close Cousin of the Crab Nebula

We present a Chandra Advanced CCD Imaging Spectrometer observation of supernova remnant G54.1+0.3. This supernova remnant is resolved into several distinct X-ray-emitting components: a central bright pointlike source (CXOU J193030.13+185214.1), a surrounding ring, bipolar elongations, plus low surface brightness diffuse emission. The spectra of these components are all well described by power-law models; the spectral index steepens with increasing distance from the pointlike source. We find no evidence for any thermal plasma emission that would correspond to shocked interstellar medium or ejecta. The observed morphological and spectral characteristics suggest that G54.1+0.3 is the closest cousin of the Crab Nebula-a pulsar wind nebula driven by a combination of equatorial and polar outflows from the putative pulsar represented by the pointlike X-ray source.

ITAL]Chandra[/ITAL] Observations of the Gravitationally Lensed System 2016+112

An observation of the gravitationally lensed system 2016+112 with the Chandra X-Ray Observatory has resolved a mystery regarding the proposed presence of a dark matter object in the lens plane of this system. The Chandra Advanced CCD Imaging Spectrometer observation has clearly detected the lensed images of 2016+112 with positions in good agreement with those reported in the optical and also detects 13 additional X-ray sources within a radius of 35. Previous X-ray observations in the direction of 2016+112 with the ROSAT HRI and ASCA Solid-State Imaging Spectrometer have interpreted the X-ray data as arising from extended emission from a dark cluster. However, the present Chandra observation can account for all the X-ray emission as originating from the lensed images and additional point X-ray sources in the field. Thus, cluster parameters based on previous X-ray observations are unreliable. We place a 3 σ upper limit on the 2-10 keV flux and luminosity of the cluster of 1.6 × 10-14 ergs s-1 cm-2 and 1.7 × 1044 ergs s-1, respectively. We estimate an upper limit on the mass-to-light ratio within a radius of 800 h kpc of M/LV < 190 h50 (M/LV)☉. None of the additional point X-ray sources are associated with the galaxy cluster members recently detected in deep optical and IR observations.