- ID:
- ivo://CDS.VizieR/J/ApJ/763/128
- Title:
- Chandra Local Volume Survey: NGC 404 sources
- Short Name:
- J/ApJ/763/128
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We present a comprehensive X-ray point-source catalog of NGC 404 obtained as part of the Chandra Local Volume Survey. A new 97ks Chandra ACIS-S observation of NGC 404 was combined with archival observations for a total exposure of ~123ks. Our survey yields 74 highly significant X-ray point sources and is sensitive to a limiting unabsorbed luminosity of ~6x10^35^erg/s in the 0.35-8keV band. To constrain the nature of each X-ray source, cross-correlations with multi-wavelength data were generated. We searched overlapping Hubble Space Telescope observations for optical counterparts to our X-ray detections, but find only two X-ray sources with candidate optical counterparts. We find 21 likely low-mass X-ray binaries (LMXBs), although this number is a lower limit due to the difficulties in separating LMXBs from background active galactic nuclei. The X-ray luminosity functions (XLFs) in both the soft and hard energy bands are presented. The XLFs in the soft band (0.5-2keV) and the hard band (2-8keV) have a limiting luminosity at the 90% completeness limit of 10^35^erg/s and 10^36^erg/s, respectively, significantly lower than previous X-ray studies of NGC 404. We find the XLFs to be consistent with those of other X-ray populations dominated by LMXBs. However, the number of luminous (>10^37^erg/s) X-ray sources per unit stellar mass in NGC 404 is lower than is observed for other galaxies. The relative lack of luminous XRBs may be due to a population of LMXBs with main-sequence companions formed during an epoch of elevated star formation ~0.5Gyr ago.
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Search Results
- ID:
- ivo://CDS.VizieR/J/ApJ/643/238
- Title:
- Chandra/2MASS sources in Cygnus OB2
- Short Name:
- J/ApJ/643/238
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- A 50ks Chandra observation of the unidentified TeV source in Cygnus reported by the HEGRA collaboration reveals no obvious diffuse X-ray counterpart. However, 240 point-like X-ray sources are detected within or nearby the extended TeV J2032+4130 source region, of which at least 36 are massive stars and two may be radio emitters. That the HEGRA source is a composite, having as a counterpart the multiple point-like X-ray sources we observe, cannot be ruled out. Indeed, the distribution of point-like X-ray sources appears nonuniform and concentrated broadly within the extent of the TeV source region. We offer a hypothesis for the origin of the very high energy gamma-ray emission in Cyg OB2 based on the local acceleration of TeV-range cosmic rays and the differential distribution of OB versus less massive stars in this association.
- ID:
- ivo://CDS.VizieR/J/ApJ/740/L34
- Title:
- Chandra monitoring of QSO J2240+0321
- Short Name:
- J/ApJ/740/L34
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We present our long-term Chandra X-ray monitoring data for the gravitationally lensed quasar Q2237+0305 with 20 epochs spanning 10 years. We easily detect microlensing variability between the images in the full (0.2-8keV), soft (0.2-2keV), and hard (2-8keV) bands at very high confidence. We also detect, for the first time, chromatic microlensing differences between the soft and hard X-ray bands. The hard X-ray band is more strongly microlensed than the soft band, suggesting that the corona above the accretion disk thought to generate the X-rays has a non-uniform electron distribution, in which the hotter and more energetic electrons occupy more compact regions surrounding the black holes. Both the hard and soft X-ray bands are more strongly microlensed than the optical (rest-frame UV) emission, indicating that the X-ray emission is more compact than the optical, confirming the microlensing results from other lenses.
- ID:
- ivo://CDS.VizieR/J/ApJ/879/112
- Title:
- Chandra multi-epoch study of the spiral gal. NGC7331
- Short Name:
- J/ApJ/879/112
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- X-ray point sources in galaxies are dominated by X-ray binaries (XRBs) that are variables or transients, and whether their variability would alter the X-ray luminosity functions (XLFs) is still in debate. Here we report on NGC 7331 as an example to test this with seven Chandra observations. Their detection limit is 7x10^37^erg/s in the energy range 0.3-8.0keV by assuming a power-law (PL) spectral model with a photon index of 1.7. We detected 55 X-ray sources. Thirteen of them are variables, of which three are transients, and some of the sources possess a bimodal feature in their luminosity-hardness ratio, which is often observed among XRBs. Nine more ultraluminous X-ray sources are found in comparison with previous studies and eight are likely to be low-mass or high-mass XRBs. Twenty-one optical counterpart candidates are found based on the Hubble Space Telescope images, but we cannot rule out the possibility of positional coincidence. The spectral analysis of SN 2014C shows a trend of increasing soft photons and decreasing hydrogen column densities as its outer shell expands. We fit the seven incompleteness-corrected XLFs to both a PL and a PL with an exponential cut-off (PLC) model using the Bayesian method, which is used for the first time in XLF fitting. The hierarchical PLC model can describe the XLF of NGC 7331 best with a slope of ~0.5 and a luminosity cut-off around 8x10^38^erg/s. This study proves that multi-epoch observations decrease the deviation due to the variable luminous sources in XLFs.
- ID:
- ivo://CDS.VizieR/J/ApJ/644/829
- Title:
- Chandra normal galaxies at intermediate redshift
- Short Name:
- J/ApJ/644/829
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We have investigated 136 Chandra extragalactic sources, including 93 galaxies with narrow emission lines (NELGs) and 43 with only absorption lines (ALGs). Based on fX/fO, LX, X-ray spectral hardness, and optical emission-line diagnostics, we have conservatively classified 36 normal galaxies and 71 AGNs. Their redshift ranges from 0.01 to 1.2, with normal galaxies in the range z=0.01-0.3. Our normal galaxies appear to share characteristics with local galaxies, as expected from the X-ray binary populations and the hot interstellar matter (ISM). In conjunction with normal galaxies found in other surveys, we found no statistically significant evolution in LX/LB, within the limited z range (<~0.1).
- ID:
- ivo://CDS.VizieR/J/A+A/418/509
- Title:
- Chandra observation of M67
- Short Name:
- J/A+A/418/509
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We present the results of a 47-ks Chandra/ACIS observation of the old open cluster M67. We detected 25 proper-motion cluster members (including ten new sources) and 12 sources (all new) that we suspect to be members from their locations close to the main sequence (1<B-V<1.7). Of the detected members, 23 are binaries.
- ID:
- ivo://CDS.VizieR/J/AJ/132/1372
- Title:
- Chandra observation of NGC 6822
- Short Name:
- J/AJ/132/1372
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- Chandra observed the nearby dwarf galaxy NGC 6822. There are 70 sources in the Chandra field, two of which are fairly extended and likely background clusters of galaxies. A third source was resolved by Chandra that has the same size and position as a known supernova remnant. The suspected variability detected from this source in previous missions is shown to be in error. The majority of the remaining 67 sources are consistent with background sources. Of the 61 sources detected above a completeness limit of 10 events, we estimate that 9+/-4+/-8 are associated with the galaxy, including both systematic and statistical errors. We compare the X-ray positions of all sources with various catalogs and Hubble Space Telescope data and offer tentative identifications for several. Based on the mass and star formation rate of NGC 6822, we expect only about 10 sources, mostly high-mass systems.
- ID:
- ivo://CDS.VizieR/J/PASJ/57/135
- Title:
- Chandra observation of NGC 2146
- Short Name:
- J/PASJ/57/135
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We present six monitoring observations of the starburst galaxy NGC 2146 using the Chandra X-ray Observatory. We detected 67 point sources in the field of view of the ACIS-S detector. Six of these sources were Ultra-Luminous X-ray Sources, the brightest of which had a luminosity of 5x10^39^erg/s. One of them, with a luminosity of ~1x10^39^erg/s, is coincident with the dynamical center location, which may be a low-luminosity active galactic nucleus. We have produced a table where the positions and main characteristics of the detected sources are reported. A comparison between the positions of the X-ray sources and those detected in NIR or radio indicates no definite counterpart. We have derived a logN-logS relation and a luminosity function. The luminosity function has a slope of 0.71 above a detection limit, which is similar to those found in other starburst galaxies. Diffuse emissions were detected in both soft (0.5-2.0keV) and hard (2.0-10.0keV) energy bands. The spectra of the diffuse component were fitted with two (hard and soft) components. The hard power-law component, with a luminosity of ~4x10^39^erg/s, is likely to have originated by unresolved point sources.
- ID:
- ivo://CDS.VizieR/J/ApJ/777/7
- Title:
- Chandra observations of 8 bulgeless disk galaxies
- Short Name:
- J/ApJ/777/7
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We have used Chandra observations of eight bulgeless disk galaxies to identify new ultraluminous X-ray source (ULX) candidates, study their high-mass X-ray binary (HMXB) population, and search for low-luminosity active galactic nuclei (AGNs). We report the discovery of 16 new ULX candidates in our sample of galaxies. Eight of these are found in the star forming galaxy NGC 337, none of which are expected to be background contaminants. The HMXB luminosity function of NGC 337 implies a star formation rate (SFR) of 6.8_-3.5_^+4.4^M_{sun}/yr, consistent at 1.5{sigma} with a recent state of the art SFR determination. We also report the discovery of a bright ULX candidate (X-1) in ESO 501-23. X-1's spectrum is well fit by an absorbed power law with {Gamma}=1.18_-0.11_^+0.19^ and N_H_=1.13_-1.13_^+7.07^/cm2, implying a 0.3-8keV flux of 1.08_-0.07_^+0.05^x10^-12^erg/s/cm2. Its X-ray luminosity (L_X_) is poorly constrained due to uncertainties in the host galaxy's distance, but we argue that its spectrum implies L_X_>10^40^erg/s. An optical counterpart to this object may be present in an Hubble Space Telescope image. We also identify ULX candidates in IC 1291, PGC 3853, NGC 5964, and NGC 2805. We find no evidence of nuclear activity in the galaxies in our sample, placing a flux upper limit of 4x10^-15^erg/s/cm2 on putative AGN. Additionally, the Type II-P supernova SN 2011DQ in NGC 337, which exploded two months before our X-ray observation, is undetected.
- ID:
- ivo://CDS.VizieR/J/AJ/137/3210
- Title:
- Chandra observations of h Persei
- Short Name:
- J/AJ/137/3210
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We describe Chandra/ACIS-I observations of the massive ~13-14Myr-old cluster, h Persei, part of the famous Double Cluster (h and {chi} Per) in Perseus. Combining the list of Chandra-detected sources with new optical/IR photometry and optical spectroscopy reveals ~165 X-ray bright stars with V<~23. Roughly 142 have optical magnitudes and colors consistent with cluster membership.