- ID:
- ivo://CDS.VizieR/J/A+A/631/A150
- Title:
- Softly X-raying the gamma-ray sky I.
- Short Name:
- J/A+A/631/A150
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- BL Lac objects are an extreme type of active galactic nuclei (AGNs) that belong to the largest population of gamma-ray sources: blazars. This class of AGNs shows a double-bumped spectral energy distribution that is commonly described in terms of a synchrotron self-Compton (SSC) emission process, whereas the low-energy component that dominates their emission between the infrared and the X-ray band is tightly connected to the high-energy component that peaks in the gamma-rays. Two strong connections that link radio and mid-infrared emission of blazars to the emission in the gamma-ray band are well established. They constitute the basis for associating gamma-ray sources with their low-energy counterparts. We searched for a possible link between X-ray and gamma-ray emissions for the subclass of BL Lacs using all archival Swift/XRT observations combined with Fermi data for a selected sample of 351 sources. Analyzing ~2400ks of Swift/XRT observations that were carried out until December 2018, we discovered that above the gamma-ray flux threshold Fgamma~=3x10^-12^erg/cm^2^/s, 96% of all Fermi BL Lacs have an X-ray counterpart that is detected with signal-to-noise ratio >3. We did not find any correlation or clear trend between X-ray and gamma-ray fluxes and/or spectral shapes, but we discovered a correlation between the X-ray flux and the mid-infrared color. Finally, we discuss on a possible interpretation of our results in the SSC framework.
Number of results to display per page
Search Results
- ID:
- ivo://CDS.VizieR/J/MNRAS/426/2668
- Title:
- Soft X-ray emission of Type Ia SN progenitors
- Short Name:
- J/MNRAS/426/2668
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We present an analysis of Chandra observations of the position of 10 nearby (<25Mpc) Type Ia supernovae, taken before the explosions. No sources corresponding to progenitors were found in any of the observations. We calculated upper limits on the bolometric luminosities of the progenitors assuming blackbody X-ray spectra with temperatures of 30-150eV. This is inspired by the fact that luminous super-soft X-ray sources have been suggested as the direct progenitors of Type Ia supernovae. The upper limits of two supernovae in our sample are comparable to the luminosities of the brightest observed super-soft sources, ruling out such sources as the progenitors of these supernovae. In contrast to Liu et al. (2012ApJ...749..141L), we find that for SN2011fe we can rule out Eddington luminosity systems for blackbody temperatures as low as 40eV. Our findings are consistent with statistical studies comparing the observed Type Ia supernova rate to the number of super-soft sources or the integrated X-ray luminosity in external galaxies. This suggests that either the progenitors of Type Ia supernovae are not accreting, nuclear burning white dwarfs or that they do not look like the classical super-soft sources, e.g. because they are obscured.
- ID:
- ivo://CDS.VizieR/J/A+A/368/797
- Title:
- Soft X-ray properties of Seyfert galaxies
- Short Name:
- J/A+A/368/797
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We present a catalogue of ROSAT detected sources in the sample of spectroscopically selected Seyfert 1 and Seyfert 2 galaxies of Rafanelli et al. (1995AJ....109.1546R). The catalogue contains 102 Seyfert 1 and 36 Seyfert 2 galaxies. The identification is based on X-ray contour maps overlaid on optical images taken from the Digitized Sky Survey. We have derived the basic spectral and timing properties of the X-ray detected Seyfert galaxies. For Seyfert 1 galaxies a strong correlation between photon index and X-ray luminosity is detected. We confirm the presence of generally steeper X-ray continua in narrow-line Seyfert 1 galaxies (NLS1s) compared to broad-line Seyfert 1 galaxies. Seyfert 2 galaxies show photon indices similar to those of NLS1s. Whereas a tendency for an increasing X-ray luminosity with increasing interaction strength is found for Seyfert 1 galaxies, such a correlation is not found for Seyfert 2 galaxies. For Seyfert 1 galaxies we found also a strong correlation for increasing far-infrared luminosity with increasing interaction strength. Both NLS1s and Seyfert 2 galaxies show the highest values of far-infrared luminosity compared to Seyfert 1 galaxies, suggesting that NLS1s and Seyfert 2 galaxies host strong (circumnuclear) star formation. For variable Seyfert galaxies we present the X-ray light curves obtained from the ROSAT All-Sky Survey and from ROSAT PSPC and HRI pointed observations. Besides the expected strong short- and long-term X-ray variability in Seyfert 1 galaxies, we find indications for X-ray flux variations in Seyfert 2 galaxies.
- ID:
- ivo://CDS.VizieR/J/AJ/127/156
- Title:
- Soft X-Ray-Selected AGNs complete sample
- Short Name:
- J/AJ/127/156
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We present the optical spectra and simple statistical analysis for a complete sample of 110 soft X-ray-selected AGNs. About half of the sources are narrow-line Seyfert 1 galaxies (NLS1's), which have the steepest X-ray spectra, the strongest Fe II emission, and slightly weaker [O III] {lambda}5007 emission than broad-line Seyfert 1's (BLS1's). Kolmogorov-Smirnov tests show that NLS1's and BLS1's have clearly different distributions of the X-ray spectral slope {alpha}_X_, X-ray short-term variability, and Fe II equivalent widths and luminosity and Fe II/H{beta} ratios.
- ID:
- ivo://CDS.VizieR/J/A+A/368/835
- Title:
- Soft X-ray sources in the Galactic Center region
- Short Name:
- J/A+A/368/835
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We present a catalogue of 107 point-like X-ray sources derived from a systematic analysis of all the ROSAT PSPC observations of the galactic center region performed in 1992-1993. Besides SgrA*, the massive black hole at the galactic center, 41 X-ray sources have been positionally associated with already classified objects. Twenty are identified with foreground stars and five with known Low Mass X-ray Binaries. The majority of the sources in our catalogue still remains unidentified. They are hard and/or severely absorbed and probably represent a large population of X-ray binaries located in the galactic center region, accreting at low accretion rates, and still largely unknown.
866. Soft X-ray standards
- ID:
- ivo://CDS.VizieR/J/A+A/458/541
- Title:
- Soft X-ray standards
- Short Name:
- J/A+A/458/541
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We analyze the Chandra LETG+HRC observations of the white dwarfs HZ43A and Sirius B and of the neutron star RX J185635-3754 with the aim of resolving current uncertainties in the soft X-ray spectral fluxes and photospheric parameters of the three stars. We apply the derived photon spectra to a cross-calibration of the LETG+HRC-S with the short-wavelength EUVE spectrometer and the ROSAT PSPC.
- ID:
- ivo://CDS.VizieR/J/ApJ/721/901
- Title:
- Solar quiescent filament channels
- Short Name:
- J/ApJ/721/901
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We present a study of the structure and dynamics of quiescent filament channels observed by Hinode/XRT and STEREO/EUVI at the solar minimum 23/24 from 2006 November to 2008 December. For 12 channels identified on the solar disk (Group I channels), we find that the morphology of the structure on the two sides of the channel is asymmetric in both X-rays and EUV: the eastern side has curved features while the western side has straight features. We interpret the results in terms of a magnetic flux rope model. The asymmetry in the morphology is due to the variation in axial flux of the flux rope along the channel, which causes the field lines from one polarity to turn into the flux rope (curved feature), while the field lines from the other polarity are connected to very distant sources (straight). For most of the 68 channels identified by cavities at the east and west limbs (Group II channels), the asymmetry cannot be clearly identified, which is likely due to the fact that the axial flux may be relatively constant along such channels. Corresponding cavities are identified only for 5 of the 12 Group I channels, while Group II channels are identified for all of the 68 cavity pairs. The studied filament channels are often observed as dark channels in X-rays and EUV. Sheared loops within Group I channels are often seen in X-rays, but are rarely seen in Group II channels as shown in the X-ray Telescope daily synoptic observations. A survey of the dynamics of studied filament channels shows that filament eruptions occur at an average rate of 1.4 filament eruptions per channel per solar rotation.
- ID:
- ivo://CDS.VizieR/J/ApJ/891/54
- Title:
- Solar X-ray flares and associated CME speeds & widths
- Short Name:
- J/ApJ/891/54
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We recently repeated an earlier analysis by Garcia showing that large (>=M3.0) solar X-ray flares associated with solar energetic particle (SEP) events have significantly lower peak X-ray flux ratios R=(0.04-0.5nm)/(0.1-0.8nm), proxies for flare peak temperatures, than those without SEP events. As we expect SEP events to be produced by shocks ahead of fast coronal mass ejections (CMEs), a smaller R for an X-ray flare of a given peak flux Fp should also be more likely to be accompanied by a fast (Vcme>1000km/s) CME. We confirm this expectation, examine the role played by the ratios R in correlations between Fp and CME speeds Vcme, and then compare CME widths W, Vcme, and R with each other. We consider an apparent conflict between a global scaling model of eruptive events showing Vcme scaling with higher R and our confirmation that the Garcia analysis implies that faster CMEs are associated with flares of lower R. The R values are examined for 16 large flares of the well-studied AR 12192, for which nearly all flares had no associated CMEs. Those flares share the same high values of R as other active region (AR) flares with no CMEs. We also find that small (<M3.0) flares of filament eruptions leading to SEP events share the lower R values of larger flares with fast CMEs.
- ID:
- ivo://CDS.VizieR/J/A+A/467/585
- Title:
- Sources detected by ISGRI
- Short Name:
- J/A+A/467/585
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- In its first 4 years of observing the sky above 20keV, INTEGRAL-ISGRI has detected 500 sources, around half of which are new or unknown at these energies. Follow-up observations at other wavelengths revealed that some of these sources feature unusually large column densities, long pulsations, and other interesting characteristics. We investigate where new and previously-known sources detected by ISGRI fit in the parameter space of high-energy objects, and we use the parameters to test correlations expected from theoretical predictions. For example, the influence of the local absorbing matter on periodic modulations is studied for Galactic High-Mass X-ray Binaries (HMXBs) with OB supergiant and Be companions. We examine the spatial distribution of different types of sources in the Milky Way using various projections of the Galactic plane, in order to highlight signatures of stellar evolution and to speculate on the origin of the group of sources whose classifications are still uncertain.
- ID:
- ivo://CDS.VizieR/J/ApJS/191/340
- Title:
- Southern Cosmology Survey. II.
- Short Name:
- J/ApJS/191/340
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We present a catalog of 105 rich and massive (M>3x10^14^M_{sun}_) optically selected clusters of galaxies extracted from 70deg^2^ of public archival griz imaging from the Blanco 4m telescope acquired over 45 nights between 2005 and 2007. We use the clusters' optically derived properties to estimate photometric redshifts, optical luminosities, richness, and masses. We complement the optical measurements with archival XMM-Newton and ROSAT X-ray data which provide additional luminosity and mass constraints on a modest fraction of the cluster sample. Two of our clusters show clear evidence for central lensing arcs; one of these has a spectacular large diameter, nearly complete Einstein Ring surrounding the brightest cluster galaxy.