ABSTRACT
Extreme high-energy peaked BL Lac objects (EHBLs) are an emerging class of blazars with exceptional spectral properties. The non-thermal emission of the relativistic jet peaks in the ...spectral energy distribution (SED) plot with the synchrotron emission in X-rays and with the gamma-ray emission in the TeV range or above. These high photon energies may represent a challenge for the standard modelling of these sources. They are important for the implications on the indirect measurements of the extragalactic background light, the intergalactic magnetic field estimate, and the possible origin of extragalactic high-energy neutrinos. In this paper, we perform a comparative study of the multiwavelength spectra of 32 EHBL objects detected by the Swift-BAT telescope in the hard X-ray band and by the Fermi-LAT telescope in the high-energy gamma-ray band. The source sample presents uniform spectral properties in the broad-band SEDs, except for the TeV gamma-ray band where an interesting bimodality seems to emerge. This suggests that the EHBL class is not homogeneous, and a possible subclassification of the EHBLs may be unveiled. Furthermore, in order to increase the number of EHBLs and settle their statistics, we discuss the potential detectability of the 14 currently TeV gamma-ray undetected sources in our sample by the Cherenkov telescopes.
The uncertainty region of the highly energetic neutrino IceCube200107A includes 3HSP J095507.9+355101 (
z
= 0.557), an extreme blazar, which was detected in a high, very hard, and variable X-ray ...state shortly after the neutrino arrival. Following a detailed multiwavelength investigation, we confirm that the source is a genuine BL Lac. This new detection differs from TXS 0506+056, which is thus far the first source associated with IceCube neutrinos, and is considered a “masquerading” BL Lac. As in the case of TXS 0506+056, 3HSP J095507.9+355101 is also way off the so-called blazar sequence. We consider 3HSP J095507.9+355101 a possible counterpart to the IceCube neutrino. Finally, we discuss some theoretical implications in terms of neutrino production.
Abstract
This paper describes the database of optical spectra of BL Lacertae (BLL) objects (Z BLL objects) available at
https://web.oapd.inaf.it/zbllac/
. At present, it contains calibrated spectra ...for 295 BLL. For about 35% of them, we report a firm measure of redshift
z
, while for 35 sources we set a lower limit on
z
based on the detection of intervening absorption systems, mainly ascribed to Mg
ii
(
λ
2800 Å). We report here on the architecture of the database and on its website front-end that permits us to filter, query, and interactively explore the data. We discuss some properties of the objects in the present data set by giving the distribution of the redshifts and reporting on the detected emission lines, which turn out to be mainly forbidden and ascribed to O
ii
(
λ
3737 Å) and O
iii
(
λ
5007 Å). Finally, we discuss on intervening absorption systems detected in 35 BLLs that allow us to set lower limits to their distance.
Abstract
Gamma-ray bursts (GRBs) are classified into long and short events. Long GRBs (LGRBs) are associated with the end states of very massive stars, while short GRBs (SGRBs) are linked to the ...merger of compact objects. GRB 200826A was a peculiar event, because by definition it was an SGRB, with a rest-frame duration of ∼0.5 s. However, this event was energetic and soft, which is consistent with LGRBs. The relatively low redshift (
z
= 0.7486) motivated a comprehensive, multiwavelength follow-up campaign to characterize its host, search for a possible associated supernova (SN), and thus understand the origin of this burst. To this aim we obtained a combination of deep near-infrared (NIR) and optical imaging together with spectroscopy. Our analysis reveals an optical and NIR bump in the light curve whose luminosity and evolution are in agreement with several SNe associated to LGRBs. Analysis of the prompt GRB shows that this event follows the
E
p,i
–
E
iso
relation found for LGRBs. The host galaxy is a low-mass star-forming galaxy, typical of LGRBs, but with one of the highest star formation rates, especially with respect to its mass (
log
M
*
/
M
⊙
=
8.6
, SFR ∼ 4.0
M
⊙
yr
−1
). We conclude that GRB 200826A is a typical collapsar event in the low tail of the duration distribution of LGRBs. These findings support theoretical predictions that events produced by collapsars can be as short as 0.5 s in the host frame and further confirm that duration alone is not an efficient discriminator for the progenitor class of a GRB.
We report on 16 BL Lacertae objects that were proposed to be at z > 1. We present spectroscopic observations secured at the 10.4 m 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 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.
ABSTRACT
Eight years after the first detection of high-energy astrophysical neutrinos by IceCube, we are still almost clueless as regards to their origin, although the case for blazars being neutrino ...sources is getting stronger. After the first significant association at the $3\!-\!3.5\, \sigma$ level in time and space with IceCube neutrinos, i.e. the blazar TXS 0506+056 at z = 0.3365, some of us have in fact selected a unique sample of 47 blazars, out of which ∼16 could be associated with individual neutrino track events detected by IceCube. Building upon our recent spectroscopy work on these objects, here we characterize them to determine their real nature and check if they are different from the rest of the blazar population. For the first time we also present a systematic study of the frequency of masquerading BL Lacs, i.e. flat-spectrum radio quasars with their broad lines swamped by non-thermal jet emission, in a γ-ray- and IceCube-selected sample, finding a fraction >24 per cent and possibly as high as 80 per cent. In terms of their broad-band properties, our sources appear to be indistinguishable from the rest of the blazar population. We also discuss two theoretical scenarios for neutrino emission, one in which neutrinos are produced in interactions of protons with jet photons and one in which the target photons are from the broad-line region. Both scenarios can equally account for the neutrino–blazar correlation observed by some of us. Future observations with neutrino telescopes and X-ray satellites will test them out.
ABSTRACT
We present multi-object optical spectroscopy of the galaxies in the environment of 12 low-redshift (z < 0.5) quasars and of 11 inactive massive galaxies chosen to match the properties of the ...quasar host galaxies to probe physical association and possible events of recent star formation (SF). The quasars are selected from a sample of QSOs in the Sloan Digital Sky Survey (SDSS) Stripe 82 region for which both the host galaxy and the large-scale environments were previously investigated. The new observations complement those reported in our previous works on close companion galaxies of nearby quasars. For the whole data set, we find that for about half (19 out of 44) of the observed QSOs, there is at least one associated companion galaxy. In addition to the new spectroscopic observations, we add data from the SDSS data base for the full sample of objects. We find that the incidence of companion galaxies in the fields of QSO (17 per cent) is not significantly different from that of inactive galaxies (19 per cent) similar to quasar hosts in redshift and mass. Nevertheless, the companions of quasars exhibit more frequently emission lines than those of inactive galaxies, suggesting a moderate link between the nuclear activity and recent SF in their environments.
On the lensed blazar B0218+357 Falomo, R; Treves, A; Scarpa, R ...
Monthly Notices of the Royal Astronomical Society,
09/2017, Volume:
470, Issue:
3
Journal Article
Peer reviewed
Open access
Abstract
We present an optical spectrum (λλ4000–10 500) of the lensed blazar B0218+357 secured at the 10 m GTC and aimed to investigate and clarify the properties of this intriguing system. We found ...that the emission line spectrum of the blazar is characterized by only one broad emission line that interpreted as Mg ii 2800 Å yields z = 0.95. In addition, we detect narrow absorption lines of Mg ii 2800 Å and Ca ii (H,K) and Na i 5892 Å at z = 0.68437 ± 0.00005 due to intervening interstellar gas. No stellar absorption features attributable to the lens galaxy are revealed. Thus, the assumed redshift of the lens is dubious. The continuum spectrum of the object exhibits a remarkable drop towards the short wavelengths likely due to a significant extinction. This extinction cannot be produced in the lens galaxy at z = 0.684 with any value of RV
under the assumption that the intrinsic shape of the blazar is dominated by a power-law emission. However, the observed continuum is consistent with a power-law emission assuming a standard (RV
= 3.1) extinction at the source redshift (z = 0.95) as supported also by the presence of Mg ii absorptions at the same redshift. HST images of B0218+357 exhibit the double image of the source together with extended image of a face on spiral galaxy. We argue that this galaxy is possibly not the lensing galaxy but the host galaxy of the blazar. This has substantial consequences on the models of the system and on the derived values of the Hubble constant.
The determination of the redshift of extragalactic gamma-ray sources is of fundamental importance for the interpretation of their emission models and extragalactic population studies, active galactic ...nuclei classification schemes, and to study the interaction with the extragalactic background light. Here we focus on the BL Lac S2 0109+22, recently detected at very high energies. We obtained a high signal-to-noise optical spectrum at Gran Telescopio Canarias for the source over the spectral range 4000–10 000 Å, to search for spectral features of the host galaxy and/or of the nuclear source and it was compared with previous observations in order to confirm and/or dispute its redshift determination. We find the S2 0109+22 optical spectrum is well represented by a power-law continuum without any absorption or emission feature of equivalent width >0.1 Å. Based on the new optical spectrum, we are able to set a redshift lower limit z > 0.35, assuming the source is hosted by a massive elliptical galaxy typical for this class of sources. The redshift z = 0.265 proposed in the literature for this object is most probably referred to a r = 18.3 galaxy at 15 arcsec from S2 0109. This galaxy could belong to a group of faint galaxies located at z ∼ 0.26.
ABSTRACT
We present optical spectroscopy of the close companions of 22 low-redshift (z < 0.5) quasars (QSO) selected from a larger sample of QSO in the SDSS Stripe82 region for which both the host ...galaxy and the large-scale environments have been investigated in our previous work. The new observations extend the number of QSO studied in our previous paper on close companion galaxies of 12 quasars. Our analysis here covers all 34 quasars from both this work and the previously published paper. We find that half of them (15 QSO; ∼44 per cent) have at least one associated galaxy. Many (12 galaxies; ∼67 per cent) of the associated companions exhibit O ii 3727 Å emission line as signature of recent star formation. The star formation rate (SFR) of these galaxies is modest (median SFR ∼ 4.3 M⊙ yr−1). For eight QSO, we are also able to detect the starlight of the host galaxy from which three have a typical spectrum of a post-starburst galaxy. Our results suggest that quasars do not have a strong influence on the star formation of their companion galaxies.
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