- ID:
- ivo://CDS.VizieR/J/ApJ/891/170
- Title:
- 10yr of radio-to-gamma-ray obs. of 1ES 1215+30.3
- Short Name:
- J/ApJ/891/170
- Date:
- 19 Jan 2022 09:02:08
- Publisher:
- CDS
- Description:
- Blazars are known for their variability on a wide range of timescales at all wavelengths. Most studies of TeV gamma-ray blazars focus on short timescales, especially during flares. With a decade of observations from the Fermi-LAT and VERITAS, we present an extensive study of the long-term multiwavelength radio-to-gamma-ray flux-density variability, with the addition of a couple of short-time radio-structure and optical polarization observations of the blazar 1ES 1215+303 (z=0.130), with a focus on its gamma-ray emission from 100MeV to 30TeV. Multiple strong GeV gamma-ray flares, a long-term increase in the gamma-ray and optical flux baseline, and a linear correlation between these two bands are observed over the ten-year period. Typical HBL behaviors are identified in the radio morphology and broadband spectrum of the source. Three stationary features in the innermost jet are resolved by Very Long Baseline Array at 43.1, 22.2, and 15.3GHz. We employ a two-component synchrotron self-Compton model to describe different flux states of the source, including the epoch during which an extreme shift in energy of the synchrotron peak frequency from infrared to soft X-rays is observed.
« Previous |
511 - 515 of 515
|
Next »
Number of results to display per page
Search Results
- ID:
- ivo://CDS.VizieR/J/ApJ/848/103
- Title:
- ~1.5yr Swift observations of Mrk 421
- Short Name:
- J/ApJ/848/103
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We present the results of the Swift observations of the nearby BL Lac object Mrk421 during 2013 November-2015 June. The source exhibited a strong long-term variability in the 0.3-10keV band, with a maximum-to-minimum flux ratio of 13, and underwent X-ray flares by a factor of 1.8-5.2 on timescales of a few weeks or shorter. The source showed 48 instances of intraday flux variability in this period, which sometimes was observed within the 1 ks observational run. It was characterized by fractional amplitudes of 1.5(0.3)%-38.6(0.4)% and flux doubling/halving times of 2.6-20.1hr. The X-ray flux showed a lack of correlation with the TeV flux on some occasions (strong TeV flares were not accompanied by comparable X-ray activity and vice versa), indicating that the high-energy emission in Mrk421 was generated from an emission region more complex than a single zone. The best fits of the 0.3-10keV spectra were mainly obtained using the log-parabola model, showing a strong spectral variability that generally followed a "harder-when-brighter" trend. The position of the synchrotron spectral energy distribution peak showed an extreme range from a few eV to ~10keV that happens rarely in blazars.
- ID:
- ivo://CDS.VizieR/J/ApJ/815/91
- Title:
- z<0.16 CIV absorbers from HST/COS QSOs spectra
- Short Name:
- J/ApJ/815/91
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- To investigate the evolution of metal-enriched gas over recent cosmic epochs as well as to characterize the diffuse, ionized, metal-enriched circumgalactic medium, we have conducted a blind survey for CIV absorption systems in 89 QSO sightlines observed with the Hubble Space Telescope Cosmic Origins Spectrograph. We have identified 42 absorbers at z<0.16, comprising the largest uniform blind sample size to date in this redshift range. Our measurements indicate an increasing CIV absorber number density per comoving path length (dN/dX=7.5+/-1.1) and modestly increasing mass density relative to the critical density of the universe ({Omega}_CIV_=10.0+/-1.5x10^-8^) from z~1.5 to the present epoch, consistent with predictions from cosmological hydrodynamical simulations. Furthermore, the data support a functional form for the column density distribution function that deviates from a single power law, also consistent with independent theoretical predictions. As the data also probe heavy element ions in addition to CIV at the same redshifts, we identify, measure, and search for correlations between column densities of these species where components appear to be aligned in velocity. Among these ion-ion correlations, we find evidence for tight correlations between CII and SiII, CII and SiIII, and CIV and SiIV, suggesting that these pairs of species arise in similar ionization conditions. However, the evidence for correlations decreases as the difference in ionization potential increases. Finally, when controlling for observational bias, we find only marginal evidence for a correlation (86.8% likelihood) between the Doppler line width b(CIV) and column density N(CIV).
- ID:
- ivo://CDS.VizieR/J/MNRAS/457/629
- Title:
- ZFOURGE catalogue of AGN candidates
- Short Name:
- J/MNRAS/457/629
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We investigate active galactic nuclei (AGN) candidates within the FourStar Galaxy Evolution Survey (ZFOURGE) to determine the impact they have on star formation in their host galaxies. We first identify a population of radio, X-ray, and infrared-selected AGN by cross-matching the deep Ks-band imaging of ZFOURGE with overlapping multiwavelength data. From this, we construct a mass-complete (log(M*/M_{sun}_)>=9.75), AGN luminosity limited sample of 235 AGN hosts over z=0.2-3.2. We compare the rest-frame U-V versus V-J (UVJ) colours and specific star formation rates (sSFRs) of the AGN hosts to a mass-matched control sample of inactive (non-AGN) galaxies. UVJ diagnostics reveal AGN tend to be hosted in a lower fraction of quiescent galaxies and a higher fraction of dusty galaxies than the control sample. Using 160{mu}m Herschel PACS data, we find the mean specific star formation rate of AGN hosts to be elevated by 0.34-/-0.07dex with respect to the control sample across all redshifts. This offset is primarily driven by infrared-selected AGN, where the mean sSFR is found to be elevated by as much as a factor of ~5. The remaining population, comprised predominantly of X-ray AGN hosts, is found mostly consistent with inactive galaxies, exhibiting only a marginal elevation. We discuss scenarios that may explain these findings and postulate that AGN are less likely to be a dominant mechanism for moderating galaxy growth via quenching than has previously been suggested.
- ID:
- ivo://CDS.VizieR/J/ApJ/653/53
- Title:
- z~6 galaxies UV luminosity function
- Short Name:
- J/ApJ/653/53
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We have detected 506 i-dropouts (z~6 galaxies) in deep, wide-area HST ACS fields: HUDF, enhanced GOODS, and HUDF parallel ACS fields (HUDF-Ps). The contamination levels are <~8% (i.e., >~92% are at z~6). With these samples, we present the most comprehensive, quantitative analyses of z~6 galaxies yet and provide optimal measures of the UV luminosity function (LF) and luminosity density at z~6, and their evolution to z~3. We redetermine the size and color evolution from z~6 to z~3. Field-to-field variations (cosmic variance), completeness, flux, and contamination corrections are modeled systematically and quantitatively.