- ID:
- ivo://CDS.VizieR/J/A+A/538/A26
- Title:
- BL Lac objects beyond z=1.3
- Short Name:
- J/A+A/538/A26
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- Observations of the {gamma}-ray sky with Fermi led to significant advances towards understanding blazars, the most extreme class of active galactic nuclei. A large fraction of the population detected by Fermi is formed by BL Lacertae (BL Lac) objects, whose sample has always suffered from a severe redshift incompleteness due to the quasi-featureless optical spectra. Our goal is to provide a significant increase of the number of confirmed high-redshift BL Lac objects contained in the 2 LAC Fermi/LAT catalog.
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Search Results
- ID:
- ivo://CDS.VizieR/J/ApJ/861/130
- Title:
- BL Lac objects GTC low resolution spectroscopy
- Short Name:
- J/ApJ/861/130
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We report on 16 BL Lacertae objects that were proposed to be at z>1. We present spectroscopic observations secured at the 10.4m GTC that allowed us to assess the redshift of these sources. In particular, for five objects, we disprove the previous value of the redshift reported in the literature and found that they lie at z<1. Moreover, two of them exhibit broad emission lines that are not characteristic of BL Lacertae objects. On the other hand, for eight targets, we improve the tentative value of z, previously based on only one feature, by detecting a number of emission lines. Finally, in three cases, we detect the onset of the Ly{alpha} forest at z>2.50. Based on the new high quality spectra, we found that only half of the observed objects can be classified as bona-fide BL Lacs.
- ID:
- ivo://CDS.VizieR/J/A+A/640/A132
- Title:
- BL Lacs optical light curves & X-ray prop.
- Short Name:
- J/A+A/640/A132
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- It has become evident that one-zone synchrotron self-Compton models are not always adequate for very high-energy (VHE) gamma-ray-emitting blazars. While two-component models perform better, they are difficult to constrain due to the large number of free parameters. In this work, we make a first attempt at taking into account the observational constraints from very long baseline interferometry (VLBI) data, long-term light curves (radio, optical, and X-rays), and optical polarisation to limit the parameter space for a two-component model and test whether or not it can still reproduce the observed spectral energy distribution (SED) of the blazars. We selected five TeV BL Lac objects based on the availability of VHE gamma-ray and optical polarisation data. We collected constraints for the jet parameters from VLBI observations. We evaluated the contributions of the two components to the optical flux by means of decomposition of long-term radio and optical light curves as well as modelling of the optical polarisation variability of the objects. We selected eight epochs for these five objects based on the variability observed at VHE gamma rays, for which we constructed the SEDs that we then modelled with a two-component model. We found parameter sets which can reproduce the broadband SED of the sources in the framework of two-component models considering all available observational constraints from VLBI observations. Moreover, the constraints obtained from the long-term behaviour of the sources in the lower energy bands could be used to determine the region where the emission in each band originates. Finally, we attempt to use optical polarisation data to shed new light on the behaviour of the two components in the optical band. Our observationally constrained two-component model allows explanation of the entire SED from radio to VHE with two co-located emission regions.
- ID:
- ivo://CDS.VizieR/J/A+A/623/A175
- Title:
- 2015 BL Lac VHE gamma-ray flare
- Short Name:
- J/A+A/623/A175
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- The mechanisms producing fast variability of the {gamma}-ray emission in active galactic nuclei (AGNs) are under debate. The MAGIC telescopes detected a fast, very-high-energy (VHE, E>100GeV) {gamma}-ray flare from BL Lacertae on 2015 June 15. The flare had a maximum flux of (1.5+/-0.3)x10^-10^photons/cm^2^/s and halving time of 26+/-8min. The MAGIC observations were triggered by a high state in the optical and high-energy (HE, E>100MeV) {gamma}-ray bands. In this paper we present the MAGIC VHE {gamma}-ray data together with multi-wavelength data from radio, optical, X-rays, and HE {gamma} rays from 2015 May 1 to July 31. Well-sampled multi-wavelength data allow us to study the variability in detail and compare it to the other epochs when fast, VHE {gamma}-ray flares have been detected from this source. Interestingly, we find that the behaviour in radio, optical, X-rays, and HE {gamma}-rays is very similar to two other observed VHE {gamma}-ray flares. In particular, also during this flare there was an indication of rotation of the optical polarization angle and of activity at the 43GHz core. These repeating patterns indicate a connection between the three events. We also test modelling of the spectral energy distribution based on constraints from the light curves and VLBA observations, with two different geometrical setups of two-zone inverse Compton models. In addition we model the {gamma}-ray data with the star-jet interaction model. We find that all of the tested emission models are compatible with the fast VHE {gamma}-ray flare, but all have some tension with the multi-wavelength observations.
1775. Blobs in AT Cnc
- ID:
- ivo://CDS.VizieR/J/MNRAS/465/739
- Title:
- Blobs in AT Cnc
- Short Name:
- J/MNRAS/465/739
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- The Z Cam-type dwarf nova AT Cancri (AT Cnc) displays a classical nova (CN) shell, demonstrating that mass transfer in cataclysmic binaries decreases substantially after a CN eruption. The hibernation scenario of cataclysmic binaries predicts such a decrease, on a time-scale of a few centuries. In order to measure the time since AT Cnc's last CN eruption, we have measured the radial velocities of a hundred clumps in its ejecta with SITELLE, Canada-France-Hawaii Telescope's recently commissioned imaging Fourier transform spectrometer. These range from -455 to +490km/s. Coupled with the known distance to AT Cnc of 460pc, the size of AT Cnc's shell, and a simple model of nova ejecta deceleration, we determine that the last CN eruption of this system occurred 330^+135^_-90_yr ago. This is the most rapid transition from a high mass-transfer rate, nova-like variable to a low mass-transfer rate, dwarf nova yet measured, and in accord with the hibernation scenario of cataclysmic binaries. We conclude by noting the similarity in the deduced outburst date (within a century of 1686 CE) of AT Cnc to a 'guest star' reported in the constellation Cancer by Korean observers in 1645 CE.
- ID:
- ivo://CDS.VizieR/J/A+A/600/A65
- Title:
- B2 0924+30 LOFAR HBA and WSRT maps
- Short Name:
- J/A+A/600/A65
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- Using LOFAR (LOw Frequency ARray), Westerbork telescope and survey data, we map the spectral index and age of the remnant radio galaxy by using different ageing models.
1777. BLOX Cluster catalog
- ID:
- ivo://CDS.VizieR/J/A+A/470/821
- Title:
- BLOX Cluster catalog
- Short Name:
- J/A+A/470/821
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- The mass function of galaxy clusters is an important cosmological probe. Differences in the selection method could potentially lead to biases when determining the mass function. From the optical and X-ray data of the XMM-Newton Follow-Up Survey, we obtain a sample of galaxy cluster candidates using weak gravitational lensing, the optical Postman matched filter method, and a search for extended X-ray sources. We develop our weak lensing search criteria by testing the performance of the aperture mass statistic on realistic ray-tracing simulations matching our survey parameters and comparing two filter functions. We find that the dominant noise source for our survey is shape noise and that spurious cluster detection due to projections of large-scale structures are negligible. Our full cluster catalog has 155 cluster candidates, 116 found with the Postman matched filter, 59 extended X-ray sources, and 31 shear selected potential clusters. Most of these cluster candidates were not previously known. The present catalog will be a solid foundation for studying possible selection effects in either method.
- ID:
- ivo://CDS.VizieR/J/MNRAS/438/557
- Title:
- BLR-less AGNs in Stripe82
- Short Name:
- J/MNRAS/438/557
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- This is the first paper in a dedicated series to study the properties of the optically-selected broad-line-region-less (BLR-less) active galactic nuclei (AGNs; with no-hidden central broad emission line regions). We carried out a systematic search for the BLR-less AGNs through the Sloan Digital Sky Survey Legacy Survey (SDSS Stripe82 Database). Based on the spectral decomposition results for all the 136 676 spectroscopic objects (galaxies and quasars) with redshift less than 0.35 covered by the SDSS Stripe82 region, our spectroscopic sample for the BLR-less AGNs includes 22 693 pure narrow line objects without broad emission lines but with apparent AGN continuum emission R_AGN_>0.3 and apparent stellar lights R_ssp_>0.3. Then, using the properties of the photometry magnitude RMS (RMS) and Pearson's coefficients (R_1,2_) between two different SDSS band light curves: RMS_k_>3xRMS_Mk_ and R_1,2_>~0.8, the final 281 pure narrow line objects with true photometry variabilities are our selected reliable candidates for the BLR-less AGNs. The selected candidates with higher confidence levels not only have the expected spectral features of the BLR-less AGNs, but also show significant true photometry variabilities. The reported sample enlarges at least four times the current sample of the BLR-less AGNs, and will provide more reliable information to explain the lack of the BLRs of AGNs in our following studies.
- ID:
- ivo://CDS.VizieR/J/MNRAS/399/195
- Title:
- Blue and red spectra of {omega} Cen HB stars
- Short Name:
- J/MNRAS/399/195
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- The multiphase interstellar medium (ISM) is highly structured, on scales from the size of the Solar System to that of a galaxy. In particular, small-scale structures are difficult to study and hence are poorly understood. We used the multiplex capabilities of the AAOmega spectrograph at the Anglo-Australian Telescope to create a half-square-degree map of the neutral and low-ionized ISM in front of the nearby (~5kpc), most massive Galactic globular cluster, {omega} Centauri. Its redshifted, metal-poor and hot horizontal branch stars probe the medium-strong CaII K and NaI D2 line absorption, and weak absorption in the {lambda}5780 and {lambda}5797 diffuse interstellar bands (DIBs), on scales around a parsec. The kinematical and thermodynamical picture emerging from these data is that we predominantly probe the warm neutral medium and weakly ionized medium of the Galactic Disc-Halo interface, ~0.3-1kpc above the mid-plane. A comparison with Spitzer Space Telescope 24um and DIRBE/IRAS maps of the warm and cold dust emission confirms that both NaI and CaII trace the overall column density of the warm neutral and weakly ionized medium. Clear signatures are seen of the depletion of calcium atoms from the gas phase into dust grains.
- ID:
- ivo://CDS.VizieR/J/ApJS/89/85
- Title:
- Blue and red supergiants in M33
- Short Name:
- J/ApJS/89/85
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We present a catalog of blue and red stars in M33 based on photographic photometry of over 65,000 objects extracted from plates taken with the 3.6m Canada-France-Hawaii Telescope (CFHT) and the 2.0m Rozhen (Bulgarian) Telescope. The completeness limit of the various surveys are estimated here to be V=19.5mag for those stars situated in crowed associations, and V=20.0mag for stars in the interarm fields. We list magnitudes and positions for 2112 blue stars, defined by (U-V)<0.0mag, and V<19.5mag, and 389 red stars defined by (B-V)>1.8mag and V<19.5mag. Of these, 1156 are candidate O stars on the basis of (U-V)<-0.9mag.
