- ID:
- ivo://CDS.VizieR/J/ApJ/758/105
- Title:
- Chandra observations of NGC2903 central regions
- Short Name:
- J/ApJ/758/105
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We present a deep Chandra observation of the central regions of the late-type barred spiral galaxy NGC 2903. The Chandra data reveal soft (kT_e_~0.2-0.5keV) diffuse emission in the nuclear starburst region and extending ~2' (~5kpc) to the north and west of the nucleus. Much of this soft hot gas is likely to be from local active star-forming regions; however, besides the nuclear region, the morphology of hot gas does not strongly correlate with the bar or other known sites of active star formation. The central ~650pc radius starburst zone exhibits much higher surface brightness diffuse emission than the surrounding regions and a harder spectral component in addition to a soft component similar to the surrounding zones. We interpret the hard component as also being of thermal origin with kT_e_~3.6keV and to be directly associated with a wind fluid produced by supernovae and massive star winds similar to the hard diffuse emission seen in the starburst galaxy M82. The inferred terminal velocity for this hard component, ~1100km/s, exceeds the local galaxy escape velocity suggesting a potential outflow into the halo and possibly escape from the galaxy gravitational potential. Morphologically, the softer extended emission from nearby regions does not display an obvious outflow geometry. However, the column density through which the X-rays are transmitted is lower in the zone to the west of the nucleus compared to that from the east and the surface brightness is relatively higher suggesting some of the soft hot gas originates from above the disk: viewed directly from the western zone but through the intervening disk of the host galaxy along sight lines from the eastern zone. There are several point-like sources embedded in the strong diffuse nuclear emission zone. Their X-ray spectra show them to likely be compact binaries. None of these detected point sources are coincident with the mass center of the galaxy and we place an upper limit luminosity from any point-like nuclear source to be <2x10^38^erg/s in the 0.5-8.0keV band, which indicates that NGC 2903 lacks an active galactic nucleus. Heating from the nuclear starburst and a galactic wind may be responsible for preventing cold gas from accreting onto the galactic center.
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- ID:
- ivo://CDS.VizieR/J/ApJ/869/171
- Title:
- Chandra observations of NuSTAR sources
- Short Name:
- J/ApJ/869/171
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- The Nuclear Spectroscopic Telescope Array (NuSTAR) serendipitous survey has already uncovered a large number of active galactic nuclei (AGNs), providing new information about the composition of the cosmic X-ray background. For AGNs off the Galactic plane, it has been possible to use existing X-ray archival data to improve source localizations, identify optical counterparts, and classify the AGNs with optical spectroscopy. However, near the Galactic plane, better X-ray positions are necessary to achieve optical or near-IR identifications due to the higher levels of source crowding. Thus, we have used observations with the Chandra X-ray Observatory to obtain the best possible X-ray positions. With eight observations, we have obtained coverage for 19 NuSTAR serendips within 12{deg} of the plane. One or two Chandra sources are detected within the error circle of 15 of the serendips, and we report on these sources and search for optical counterparts. For one source (NuSTAR J202421+3350.9), we obtained a new optical spectrum and detected the presence of hydrogen emission lines. The source is Galactic, and we argue that it is likely a cataclysmic variable. For the other sources, the Chandra positions will enable future classifications in order to place limits on faint Galactic populations, including high-mass X-ray binaries and magnetars.
- ID:
- ivo://CDS.VizieR/J/ApJ/549/441
- Title:
- Chandra observations of Orion Trapezium
- Short Name:
- J/ApJ/549/441
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We used the High-Energy Transmission Grating Spectrometer on board the Chandra X-Ray Observatory to perform two observations, separated by 3 weeks, of the Orion Trapezium region. The zeroth-order images on the Advanced CCD Imaging Spectrometer provide spatial resolution of 0.5" and moderate energy resolution. Within a 160"x140" region around the Orion Trapezium, we resolve 111 X-ray sources with luminosities between 7x10^28^ and 2x10^32^ergs/s. We do not detect any diffuse emission. All but six sources are identified.
- ID:
- ivo://CDS.VizieR/J/MNRAS/492/719
- Title:
- Chandra observations of 2106 radio-quiet QSOs
- Short Name:
- J/MNRAS/492/719
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We present Chandra observations of 2106 radio-quiet quasars in the redshift range 1.7<=z<=2.7 from the Sloan Digital Sky Survey (SDSS), through data release fourteen (DR14, 2018ApJS..235...42A), that do not contain broad absorption lines (BAL) in their rest-frame UV spectra. This sample adds over a decade worth of SDSS and Chandra observations to our previously published sample of 139 quasars from SDSS DR5 which is still used to correlate X-ray and optical/UV emission in typical quasars. We fit the SDSS spectra for 753 of the quasars in our sample that have high-quality (large exposure time and small off-axis observation angle) X-ray observations, and analyze their X-ray properties (aox and daox) with respect to the measured CIV and MgII emission-line rest-frame equivalent width (EW) and the CIV emission-line blueshift. We find significant correlations (at the >=99.99% level) between aox and these emission-line parameters, as well as between daox and CIV EW. Slight correlations are found between daox and CIV blueshift, MgII EW, and the ratio of CIV EW to MgII EW. The best-fit trend in each parameter space is used to compare the X-ray weakness (daox) and optical/UV emission properties of typical quasars and weak-line quasars (WLQs). The WLQs clearly deviate from the expectation for every relationship, typically exhibiting much weaker X-ray emission than predicted by the typical quasar relationships. The best-fit relationships for our typical quasars are consistent with predictions from the disk-wind quasar model. The behavior of the WLQs with respect to our typical quasars can be explained by an X-ray shielding model.
- ID:
- ivo://CDS.VizieR/J/ApJ/740/87
- Title:
- Chandra observations of radio transients
- Short Name:
- J/ApJ/740/87
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We present a 50ks Chandra/ACIS-I X-ray observation of the Bower et al. (2007ApJ...666..346B) Very Large Array archival field. The observations reach a limiting sensitivity of ~10^-4^counts/s, corresponding to a flux of a few times 10^-15^erg/s/cm^2^ for the models we explore. The Chandra observations were undertaken to search for X-ray counterparts to the eight transient sources without optical counterparts, and the two transient sources with optical counterparts seen by Bower et al. Neither of the sources with optical counterparts was detected in X-rays. One of the eight optical non-detections is associated with a marginal (2.4{sigma}) X-ray detection in our Chandra image. A second optically undetected Bower et al. transient may be associated with a z=1.29 X-ray-detected quasar or its host galaxy, or alternatively is undetected in X-rays and is a chance association with the nearby X-ray source. The X-ray flux upper limits, and the one marginal detection, are consistent with the interpretation of Ofek et al. (2010ApJ...711..517O) that the optically undetected radio transients are flares from isolated old Galactic neutron stars. The marginal X-ray detection has a hardness ratio that implies a temperature too high for a simple one-temperature neutron star model, but plausible multi-component fits are not excluded, and in any case the marginal X-ray detection may be due to cosmic rays or particle background. The X-ray flux upper limits are also consistent with flare star progenitors at >~1kpc (which would require the radio luminosity of the transient to be unusually high for such an object) or less extreme flares from brown dwarfs at distances of around 100pc.
- ID:
- ivo://CDS.VizieR/J/ApJS/243/3
- Title:
- Chandra observations of SINGS galaxies
- Short Name:
- J/ApJS/243/3
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We present new Chandra constraints on the X-ray luminosity functions (XLFs) of X-ray binary (XRB) populations, as well as their scaling relations, for a sample of 38 nearby galaxies (D=3.4-29Mpc). Our galaxy sample is drawn primarily from the Spitzer Infrared Nearby Galaxies Survey (SINGS) and contains a wealth of Chandra (5.8Ms total) and multiwavelength data, allowing for star formation rates (SFRs) and stellar masses (M_*_) to be measured on subgalactic scales. We divided the 2478 X-ray-detected sources into 21 subsamples in bins of specific SFR (sSFR=SFR/M_*_) and constructed XLFs. To model the XLF dependence on sSFR, we fit a global XLF model, containing contributions from high-mass XRBs (HMXBs), low-mass XRBs (LMXBs), and background sources from the cosmic X-ray background that respectively scale with SFR, M_*_, and sky area. We find an HMXB XLF that is more complex in shape than previously reported and an LMXB XLF that likely varies with sSFR, potentially due to an age dependence. When applying our global model to XLF data for each individual galaxy, we discover a few galaxy XLFs that significantly deviate from our model beyond statistical scatter. Most notably, relatively low-metallicity galaxies have an excess of HMXBs above ~10^38^erg/s, and elliptical galaxies that have relatively rich populations of globular clusters (GCs) show excesses of LMXBs compared to the global model. Additional modeling of how the XRB XLF depends on stellar age, metallicity, and GC specific frequency is required to sufficiently characterize the XLFs of galaxies.
- ID:
- ivo://CDS.VizieR/J/ApJ/799/163
- Title:
- Chandra observations of solar analogs
- Short Name:
- J/ApJ/799/163
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We investigate whether magnetic interaction between close-in giant planets and their host stars produce observable statistical enhancements in stellar coronal or chromospheric activity. New Chandra observations of 12 nearby (d<60pc) planet-hosting solar analogs are combined with archival Chandra, XMM-Newton, and ROSAT coverage of 11 similar stars to construct a sample inoculated against inherent stellar class and planet-detection biases. Survival analysis and Bayesian regression methods (incorporating both measurements errors and X-ray upper limits; 13/23 stars have secure detections) are used to test whether "hot Jupiter" hosts are systematically more X-ray luminous than comparable stars with more distant or smaller planets. No significant correlations are present between common proxies for interaction strength (M_P_/a^2^ or 1/a) versus coronal activity (L_X_ or L_X_/L_bol_). In contrast, a sample of 198 FGK main-sequence stars does show a significant (~99% confidence) increase in X-ray luminosity with M_P_/a^2^. While selection biases are incontrovertibly present within the main-sequence sample, we demonstrate that the effect is primarily driven by a handful of extreme hot-Jupiter systems with M_P_/a^2^>450M_Jup_AU^-2^, which here are all X-ray luminous but to a degree commensurate with their Ca II H and K activity, in contrast to presented magnetic star-planet interaction scenarios that predict enhancements relatively larger in L_X_. We discuss these results in the context of cumulative tidal spin-up of stars hosting close-in gas giants (potentially followed by planetary infall and destruction). We also test our main-sequence sample for correlations between planetary properties and UV luminosity or Ca II H and K emission, and find no significant dependence.
- ID:
- ivo://CDS.VizieR/J/ApJ/774/23
- Title:
- Chandra observations of SPT-SZ clusters
- Short Name:
- J/ApJ/774/23
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We present first results on the cooling properties derived from Chandra X-ray observations of 83 high-redshift (0.3<z<1.2) massive galaxy clusters selected by their Sunyaev-Zel'dovich signature in the South Pole Telescope data. We measure each cluster's central cooling time, central entropy, and mass deposition rate, and compare these properties to those for local cluster samples. We find no significant evolution from z~0 to z~1 in the distribution of these properties, suggesting that cooling in cluster cores is stable over long periods of time. We also find that the average cool core entropy profile in the inner ~100kpc has not changed dramatically since z~1, implying that feedback must be providing nearly constant energy injection to maintain the observed "entropy floor" at ~10keV cm^2^.
- ID:
- ivo://CDS.VizieR/J/ApJ/765/87
- Title:
- Chandra observations of the 2QZ Cluster 1004+00
- Short Name:
- J/ApJ/765/87
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We present results from a {approx}100ks Chandra observation of the 2QZ Cluster 1004+00 structure at z=2.23 (hereafter 2QZ Clus). 2QZ Clus was originally identified as an overdensity of four optically-selected QSOs at z=2.23 within a 15x15arcmin^2^ region. Narrow-band imaging in the near-IR (within the K band) revealed that the structure contains an additional overdensity of 22 z=2.23 H{alpha}-emitting galaxies (HAEs), resulting in 23 unique z=2.23 HAEs/QSOs (22 within the Chandra field of view). Our Chandra observations reveal that three HAEs in addition to the four QSOs harbor powerfully accreting supermassive black holes (SMBHs), with 2-10keV luminosities of ~(8-60)x10^43^erg/s and X-ray spectral slopes consistent with unobscured active galactic nucleus (AGN). Using a large comparison sample of 210 z=2.23 HAEs in the Chandra-COSMOS field (C-COSMOS), we find suggestive evidence that the AGN fraction increases with local HAE galaxy density. The 2QZ Clus HAEs reside in a moderately overdense environment (a factor of {approx}2 times over the field), and after excluding optically-selected QSOs, we find that the AGN fraction is a factor of {approx}3.5^+3.8^_-2.2_ times higher than C-COSMOS HAEs in similar environments. Using stacking analyses of the Chandra data and Herschel SPIRE observations at 250{mu}m, we respectively estimate mean SMBH accretion rates ((dM/dt)_BH_) and star formation rates (SFRs) for the 2QZ Clus and C-COSMOS samples.
- ID:
- ivo://CDS.VizieR/J/ApJ/589/509
- Title:
- Chandra observations of Trumpler 14 and 16
- Short Name:
- J/ApJ/589/509
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- The region around the {eta} Carinae Nebula has three OB associations, which contain a Wolf-Rayet star and several massive O3 stars. An early Chandra ACIS-I image was centered on {eta} Car and includes Trumpler 16 and part of Trumpler 14. The Chandra image confirms the well-known result that O and very early B stars are X-ray sources with LX~=10^-7^Lbol over an X-ray luminosity range of about 100. Two new, anomalously strong X-ray sources have been found among the hot star population: Tr 16-244, a heavily reddened O3 I star, and Tr 16-22, a heavily reddened O8.5 V star. Two stars have an unusually large LX/Lbol: HD 93162, a Wolf-Rayet star (and possible binary), and Tr 16-22, a possible colliding-wind binary. In addition, a population of sources associated with cool stars is detected. In the color-magnitude diagram, these X-ray sources sit above the sequence of field stars in the Carina arm. The OB stars are on average more X-ray luminous than the cool star X-ray sources. X-ray sources among A stars have X-ray luminosities similar to those of cooler stars and may be due to cooler companions. Upper limits are presented for B stars that are not detected in X-rays. These upper limits are also the upper limits for any cool companions that the hot stars may have. Hardness ratios are presented for the most luminous sources in bands 0.5-0.9, 0.9-1.5, and 1.5-2.04keV. The available information on the binary nature of the hot stars is discussed, but binarity does not correlate with X-ray strength in a simple way.