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281. Gamma ray burst localizations
ID:
ivo://CDS.VizieR/J/ApJ/446/115
Title:
Gamma ray burst localizations
Short Name:
J/ApJ/446/115
Date:
21 Oct 2021
Publisher:
CDS
Description:
We report the results of a 5 year CCD imaging program of small gamma-ray burst (GRB) error boxes from the First Interplanetary Network and an optical transient field. The fields include GBS 0010-16, GBS 0552-08, GBS 1028+46, GBS 1205+23, GBS 1412+79, OTS 1809+31, GBS 2006-22, and GBS 2252-03. A total of 274 hours of open shutter time was used to obtain multiple UBVI-filtered frames covering an area approximately twice that of the 99% confidence localizations. For 2070 objects in these fields above the survey detection limit of V~24, 79,000 calibrated photometric measurements were made. The objectives of the survey were to search for objects of unusual colors, variability, or proper motions. The final census of objects in these fields is consistent with the expected numbers of normal stars, galaxies, and proper motion objects based on statistics of large-scale surveys. While no obvious GRB optical counterparts were found, several potentially interesting objects were discovered, along with marginal evidence for a QSO excess at the rate of one per high Galactic latitude localization. The results and implications are discussed in detail along with suggestions for future work.
282. {gamma}-ray Doppler factor for Fermi blazars
ID:
ivo://CDS.VizieR/J/other/RAA/13.259
Title:
{gamma}-ray Doppler factor for Fermi blazars
Short Name:
J/other/RAA/13.2
Date:
21 Oct 2021
Publisher:
CDS
Description:
Observations suggest that gamma-ray loud blazars are strongly beamed. The Fermi mission has detected many of blazars, which provide us with a good opportunity to investigate the emission mechanism and the beaming effect in the gamma-ray region. We compiled the X-ray observations for 138 Fermi blazars (54 flat spectrum radio quasars, 36 low-peaked BL Lacertae objects, and 48 high-peaked BL Lacertae objects) and calculated their Doppler factors, {delta}_{gamma}. It is interesting that the calculated Doppler factors, {delta}_{gamma}, are strongly correlated with the gamma-ray luminosity.
283. Gamma-ray light curves of Fermi blazars
ID:
ivo://CDS.VizieR/J/ApJ/722/520
Title:
Gamma-ray light curves of Fermi blazars
Short Name:
J/ApJ/722/520
Date:
21 Oct 2021
Publisher:
CDS
Description:
This paper presents light curves as well as the first systematic characterization of variability of the 106 objects in the high-confidence Fermi Large Area Telescope Bright AGN Sample (LBAS). Weekly light curves of this sample, obtained during the first 11 months of the Fermi survey (2008 August 4-2009 July 4), are tested for variability and their properties are quantified through autocorrelation function and structure function analysis. For the brightest sources, 3 or 4 day binned light curves are extracted in order to determine power density spectra (PDSs) and to fit the temporal structure of major flares. More than 50% of the sources are found to be variable with high significance, where high states do not exceed 1/4 of the total observation range. Variation amplitudes are larger for flat spectrum radio quasars and low/intermediate synchrotron frequency peaked BL Lac objects. Autocorrelation timescales derived from weekly light curves vary from four to a dozen of weeks.
284. {gamma}-ray loud blazars
ID:
ivo://CDS.VizieR/J/ApJ/726/16
Title:
{gamma}-ray loud blazars
Short Name:
J/ApJ/726/16
Date:
21 Oct 2021
Publisher:
CDS
Description:
The radio properties of blazars detected by the Large Area Telescope (LAT) on board the Fermi Gamma-ray Space Telescope have been observed as part of the VLBA Imaging and Polarimetry Survey. This large, flux-limited sample of active galactic nuclei (AGNs) provides insights into the mechanism that produces strong {gamma}-ray emission. At lower flux levels, radio flux density does not directly correlate with {gamma}-ray flux. We find that the LAT-detected BL Lac objects tend to be similar to the non-LAT BL Lac objects, but that the LAT-detected FSRQs are often significantly different from the non-LAT FSRQs. The differences between the {gamma}-ray loud and quiet FSRQs can be explained by Doppler boosting; these objects appear to require larger Doppler factors than those of the BL Lac objects. It is possible that the {gamma}-ray loud FSRQs are fundamentally different from the {gamma}-ray quiet FSRQs. Strong polarization at the base of the jet appears to be a signature for {gamma}-ray loud AGNs.
285. Gamma-ray loud blazars optical monitoring. II.
ID:
ivo://CDS.VizieR/J/A+AS/127/445
Title:
Gamma-ray loud blazars optical monitoring. II.
Short Name:
J/A+AS/127/445
Date:
21 Oct 2021
Publisher:
CDS
Description:
New data from the optical monitoring of gamma-ray loud blazars at the Torino Astronomical Observatory are presented.
286. Gamma-ray-loud blazars optical polarization
ID:
ivo://CDS.VizieR/J/MNRAS/442/1693
Title:
Gamma-ray-loud blazars optical polarization
Short Name:
J/MNRAS/442/1693
Date:
21 Oct 2021
Publisher:
CDS
Description:
We present first results from RoboPol, a novel-design optical polarimeter operating at the Skinakas Observatory in Crete. The data, taken during the 2013 May-June commissioning of the instrument, constitute a single-epoch linear polarization survey of a sample of gamma-ray-loud blazars, defined according to unbiased and objective selection criteria, easily reproducible in simulations, as well as a comparison sample of, otherwise similar, gamma-ray-quiet blazars. As such, the results of this survey are appropriate for both phenomenological population studies and for tests of theoretical population models. We have measured polarization fractions as low as 0.015 down to Rmag of 17 and as low as 0.035 down to 18mag. The hypothesis that the polarization fractions of gamma-ray-loud and gamma-ray-quiet blazars are drawn from the same distribution is rejected at the 3{sigma} level. We therefore conclude that gamma-ray-loud and gamma-ray-quiet sources have different optical polarization properties. This is the first time this statistical difference is demonstrated in optical wavelengths. The polarization fraction distributions of both samples are well described by exponential distributions with averages of <p>=6.4^+0.9^_-0.8_x10^-2^ for gamma-ray-loud blazars, and <p>=3.2^+2.0^_-1.1_x10^-2^ for gamma-ray-quiet blazars. The most probable value for the difference of the means is 3.4^+1.5^_-2.0_x10^-2^. The distribution of polarization angles is statistically consistent with being uniform.
287. gamma-rays in Fermi blazars
ID:
ivo://CDS.VizieR/J/MNRAS/477/4749
Title:
gamma-rays in Fermi blazars
Short Name:
J/MNRAS/477/4749
Date:
17 Jan 2022 00:27:10
Publisher:
CDS
Description:
The gamma-ray emission in broad-line blazars is generally explained as inverse Compton (IC) radiation of relativistic electrons in the jet scattering optical-UV photons from the broad-line region (BLR), the so-called BLR external Compton (EC) scenario. We test this scenario on the Fermi gamma-ray spectra of 106 broad-line blazars detected with the highest significance or largest BLR, by looking for cut-off signatures at high energies compatible with {gamma}-{gamma} interactions with BLR photons. We do not find evidence for the expected BLR absorption. For 2/3 of the sources, we can exclude any significant absorption ({tau}_max_<1), while for the remaining 1/3 the possible absorption is constrained to be 1.5-2 orders of magnitude lower than expected. This result holds also dividing the spectra in high- and low-flux states, and for powerful blazars with large BLR. Only 1 object out of 10 seems compatible with substantial attenuation ({tau}_max_>5). We conclude that for 9 out of 10 objects, the jet does not interact with BLR photons. Gamma-rays seem either produced outside the BLR most of the time, or the BLR is ~100 x larger than given by reverberation mapping. This means that (i) EC on BLR photons is disfavoured as the main gamma-ray mechanism, versus IC on IR photons from the torus or synchrotron self-Compton; (ii) the Fermi gamma-ray spectrum is mostly intrinsic, determined by the interaction of the particle distribution with the seed-photon spectrum; and (iii) without suppression by the BLR, broad-line blazars can become copious emitters above 100GeV, as demonstrated by 3C 454.3. We expect the CTA sky to be much richer of broad-line blazars than previously thought.
288. Gemini GNIRS NIR spectroscopy of 50 QSOs at z>~5.7
ID:
ivo://CDS.VizieR/J/ApJ/873/35
Title:
Gemini GNIRS NIR spectroscopy of 50 QSOs at z>~5.7
Short Name:
J/ApJ/873/35
Date:
19 Jan 2022 09:09:09
Publisher:
CDS
Description:
We report initial results from a large Gemini program to observe z>~5.7 quasars with GNIRS near-IR spectroscopy. Our sample includes 50 quasars with simultaneous ~0.85-2.5{mu}m spectra covering the rest-frame ultraviolet and major broad emission lines from Ly{alpha} to MgII. We present spectral measurements for these quasars and compare with their lower redshift counterparts at z=1.5-2.3. We find that when quasar luminosity is matched, there are no significant differences between the rest-UV spectra of z>~5.7 quasars and the low-z comparison sample. High-z quasars have similar continuum and emission line properties and occupy the same region in the black hole mass and luminosity space as the comparison sample, accreting at an average Eddington ratio of ~0.3. There is no evidence for super-Eddington accretion or hypermassive (>10^10^M_{sun}_) black holes within our sample. We find a mild excess of quasars with weak CIV lines relative to the control sample. Our results, corroborating earlier studies but with better statistics, demonstrate that these high-z quasars are already mature systems of accreting supermassive black holes operating with the same physical mechanisms as those at lower redshifts.
289. Ghostly damped Ly{alpha} systems in SDSS DR14
ID:
ivo://CDS.VizieR/J/ApJ/901/123
Title:
Ghostly damped Ly{alpha} systems in SDSS DR14
Short Name:
J/ApJ/901/123
Date:
18 Feb 2022 09:18:37
Publisher:
CDS
Description:
We report the discovery of 59 new ghostly absorbers from the Sloan Digital Sky Survey Data Release 14. These absorbers, with z_abs_~z_QSO_, reveal no Ly{alpha} absorption, and they are mainly identified through the detection of strong metal absorption lines in the spectra. The number of such previously known systems is 30. The new systems are found with the aid of machine-learning algorithms. The spectra of 41 (out of total of 89) absorbers also cover the Ly{beta} spectral region. By fitting the damping wings of the Ly{beta} absorption in the stacked spectrum of 21 (out of 41) absorbers with relatively stronger Ly{beta} absorption, we measured an HI column density of log N(HI)=21.50. This column density is 0.5dex higher than that of the previous work. We also found that the metal absorption lines in the stacked spectrum of the 21 ghostly absorbers with stronger Ly{beta} absorption have similar properties as those in the stacked spectrum of the remaining systems. This circumstantial evidence strongly suggests that the majority of our ghostly absorbers are indeed DLAs.
290. Ghostly strong Lya absorbers in SDSS DR12
ID:
ivo://CDS.VizieR/J/ApJ/888/85
Title:
Ghostly strong Lya absorbers in SDSS DR12
Short Name:
J/ApJ/888/85
Date:
25 Oct 2021 10:15:53
Publisher:
CDS
Description:
We have searched the Sloan Digital Sky Survey Data Release 12 for ghostly strong Ly{alpha} (DLA) systems. These systems, located at the redshift of the quasars, show strong absorption from low-ionization atomic species but reveal no HI Ly{alpha} absorption. Our search has, for the first time, resulted in a sample of 30 homogeneously selected ghostly absorbers with z_QSO_>2.0. Thirteen of the ghostly absorbers exhibit absorption from other HI Lyman series lines. The lack of Ly{alpha} absorption in these absorbers is consistent with them being dense and compact with projected sizes smaller than the broad-line region of the background quasar. Although uncertain, the estimated median HI column density of these absorbers is logN(HI)~21.0. We compare the properties of ghostly absorbers with those of eclipsing DLAs that are high-column-density absorbers, located within 1500km/s of the quasar emission redshift and showing strong Ly{alpha} emission in their DLA trough. We discover an apparent sequence in the observed properties of these DLAs, with ghostly absorbers showing wider HI kinematics, stronger absorptions from high-ionization species, CII and SiII excited states, and a higher level of dust extinction. Since we estimate that all these absorbers have similar metallicities, logZ/Z_{sun}_~-1.0, we conclude that ghostly absorbers are part of the same population as eclipsing DLAs, except that they are denser and located closer to the central active galactic nuclei.

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