Context.
Tensions between the diffuse gamma-ray sky observed by the
Fermi
Large Area Telescope (
Fermi
-LAT) and the diffuse, high-energy neutrino sky detected by the IceCube South Pole Neutrino ...Observatory raise questions about our knowledge of high-energy neutrino sources in the gamma-ray regime. While blazars are among the most energetic persistent particle accelerators in the Universe, studies suggest that they could account for up to 10–30% of the neutrino flux measured by IceCube.
Aims.
Our recent results highlight that the associated IceCube neutrinos arrived in a local gamma-ray minimum (dip) of three strong neutrino point-source candidates. Here, we increase the sample of neutrino-source candidates in order to study their gamma-ray light curves.
Methods.
We generated the one-year
Fermi
-LAT light curve for eight neutrino-source candidate blazars (RBS 0958, GB6 J1040+0617, PKS 1313-333, TXS 0506+056, PKS 1454-354, NVSS J042025-374443, PKS 0426-380, and PKS 1502+106), centered on the detection time of the associated IceCube neutrinos. We applied the Bayesian block algorithm to the light curves to characterize their variability.
Results.
Our results indicate that GB6 J1040+0617 was in a phase of high gamma-ray activity, while none of the other seven neutrino-source candidates were statistically bright during the detection of the corresponding neutrinos; indeed, most of the time neutrinos arrived in a faint gamma-ray phase of the light curves. This suggests either that the eight source candidate blazars (associated with seven neutrino events) in our reduced sample are not the sources of the corresponding IceCube neutrinos, or that an in-source effect (e.g., the suppression of gamma rays due to high gamma-gamma opacity) complicates the multimessenger scenario of neutrino emission for these blazars.
ABSTRACT
Using blazar light curves from the optical All-Sky Automated Survey for Supernovae (ASAS-SN) and the γ-ray Fermi-LAT telescope, we performed the most extensive statistical correlation study ...between both bands, using a sample of 1180 blazars. This is almost an order of magnitude larger than other recent studies. Blazars represent more than 98 per cent of the AGNs detected by Fermi-LAT and are the brightest γ-ray sources in the extragalactic sky. They are essential for studying the physical properties of astrophysical jets from central black holes. However, their γ-ray flare mechanism is not fully understood. Multiwavelength correlations help constrain the dominant mechanisms of blazar variability. We search for temporal relationships between optical and γ-ray bands. Using a Bayesian Block Decomposition, we detect 1414 optical and 510 γ-ray flares, we find a strong correlation between both bands. Among all the flares, we find 321 correlated flares from 133 blazars, and derive an average rest-frame time delay of only 1.1$_{-8.5}^{+7.1}$ d, with no difference between the flat-spectrum radio quasars, BL Lacertae-like objects or low, intermediate, and high-synchrotron peaked blazar classes. Our time-delay limit rules out the hadronic proton-synchrotron model as the driver for non-orphan flares and suggests a leptonic single-zone model. Limiting our search to well-defined light curves and removing 976 potential but unclear ‘orphan’ flares, we find 191 (13 per cent) and 115 (22 per cent) clear ‘orphan’ optical and γ-ray flares. The presence of ‘orphan’ flares in both bands challenges the standard one-zone blazar flare leptonic model and suggests multizone synchrotron sites or a hadronic model for some blazars.
The recent spatial and temporal coincidence of the blazar TXS 0506+056 with the IceCube-detected neutrino event IC-170922A has opened up a realm of multimessenger astronomy with blazar jets as a ...plausible site of cosmic-ray acceleration. After TXS 0506+056, a second blazar, BZB J0955+3551, was recently found to be spatially coincident with the IceCube-detected neutrino event IC-200107A and undergoing its brightest X-ray flare measured so far. Here we present the results of our multifrequency campaign to study this peculiar event that includes observations with the NuSTAR, Swift, Neutron star Interior Composition Explorer (NICER), and 10.4 m Gran Telescopio Canarias (GTC). The optical spectroscopic observation from GTC secured its redshift as and the central black hole mass as . Both NuSTAR and NICER data reveal a rapid flux variability, albeit at low significance ( ). We explore the origin of the target photon field needed for the photopion production using analytical calculations and considering the observed optical-to-X-ray flux level. We conclude that seed photons may originate from outside the jet, similar to that reported for TXS 0506+056, although a scenario invoking a comoving target photon field (e.g., electron synchrotron) cannot be ruled out. The electromagnetic output from the neutrino-producing photohadronic processes are likely to make only a subdominant contribution to the observed spectral energy distribution, suggesting that the X-ray flaring event may not be directly connected with IC-200107A.
The realtime program for high-energy neutrino track events detected by the IceCube South Pole Neutrino Observatory releases alerts to the astronomical community with the goal of identifying ...electromagnetic counterparts to astrophysical neutrinos. Gamma-ray observations from the Fermi -Large Area Telescope (LAT) enabled the identification of the flaring gamma-ray blazar TXS 0506+056 as a likely counterpart to the neutrino event IC-170922A. By continuously monitoring the gamma-ray sky, Fermi -LAT plays a key role in the identification of candidate counterparts to realtime neutrino alerts. In this paper, we present the Fermi -LAT strategy for following up high-energy neutrino alerts applied to seven years of IceCube data. Right after receiving an alert, a search is performed in order to identify gamma-ray activity from known and newly detected sources that are positionally consistent with the neutrino localization. In this work, we study the population of blazars found in coincidence with high-energy neutrinos and compare them to the full population of gamma-ray blazars detected by Fermi -LAT. We also evaluate the relationship between the neutrino and gamma-ray luminosities, finding different trends between the two blazar classes BL Lacs and flat-spectrum radio quasars.
pH‐Responsive polymers have great potential in biomedical applications, including the selective delivery of preloaded drugs to tissues with low pH values. These polymers usually contain acid‐labile ...linkages such as esters and acetals/ketals. However, these linkages are only mildly pH‐responsive with relatively long half‐lives (t1/2). Orthoester linkages are more acid‐labile, but current methods suffer from synthetic challenges and are limited to the availability of monomers. To address these limitations, a sugar poly(orthoester) was synthesized as a highly pH‐responsive polymer. The synthesis was achieved by using 2,3,4‐tri‐O‐acetyl‐α‐D‐glucopyranosyl bromide as a difunctional AB monomer and tetra‐n‐butylammonium iodide (TBAI) as an effective promoter. Under optimal conditions, polymers with molecular weights of 6.9 kDa were synthesized in a polycondensation manner. The synthesized glucose poly(orthoester), wherein all sugar units were connected through orthoester linkages, was highly pH‐responsive with a half‐life of 0.9, 0.6, and 0.2 hours at pH 6, 5, and 4, respectively.
We love sugar! The synthesis of sugar‐based polymers, wherein all sugar units are connected by orthoester linkages, was achieved by polymerization of a glucose‐based difunctional AB monomer (see scheme, left). When tetra‐n‐butylammonium iodide (TBAI) was used as a promoter, polymers with molecular weights up to 6.9 kDa were synthesized in a polycondensation manner. These polymers are highly pH‐responsive with a half‐life of 0.9 hours at pH 6.
The Large Array Survey Telescope—Science Goals Ben-Ami, S.; Ofek, E. O.; Polishook, D. ...
Publications of the Astronomical Society of the Pacific,
08/2023, Letnik:
135, Številka:
1050
Journal Article
Core-collapse supernovae are among the prime candidate sources of high energy neutrinos. Accordingly, the IceCube collaboration has started a program to search for such a signal. IceCube operates an ...online search for neutrino bursts, forwarding the directions of candidate events to a network of optical telescopes for immediate follow-up observations. If a supernova is identified from the optical observations, in addition to a directional coincidence a temporal
γ
–
ν
coincidence also needs to be established. To achieve this, we present a method for estimating the supernova explosion time from its light curve using a simple model. We test the model with supernova light curve data from SN1987A, SN2006aj and SN2008D and show that the explosion times can be determined with an accuracy of better than a few hours.
Context.
The origin of the diffuse astrophysical neutrino flux observed by the IceCube experiment is still under debate. Multiple associations have been reported between high-energy neutrino events ...and individual bla/ars, such as the source TXS 0506+056, which are active galaxies with relativistic jets pointing toward Earth. From a theoretical perspective, the properties of these sources as neutrino emitters are not yet well understood.
Aims.
By systematically modeling the effect of cosmic-ray protons on the multiwavelength data from the largest sample of bright gamma-ray bla/ars to date, we expect to learn about the multi-messenger nature of the active galaxy population as a whole, as well as the relationship between neutrino production and the multiwavelength spectrum of these sources.
Methods.
We predict the emitted multiwavelength and neutrino spectrum using a self-consistent numerical radiation model applied individually to each source in the sample. We then study the properties of the full population and identify empirical relations. We focus on public multiwavelength data from the radio to the gamma-ray bands from a sample of 324 bla/ars detected by the
Fermi
Large Area Telescope (LAT), most of which are flat-spectrum radio quasars (FSRQs). This amounts to 34% of all FSRQs in the latest
Fermi
catalog.
Results.
We demonstrate that the optical and gigaelectronvolt gamma-ray broadband features are generally well described by electron emission, which helps for the location of the emission region relative to the central black hole to be constrained. For 33% of the bla/ars in our sample, a description of the observed X-ray spectrum benefits from an additional component from proton interactions, in agreement with recent studies of individual IceCube candidate bla/ars. We show that, on average, bla/ars that are brighter in gigaelectronvolt gamma rays have a higher neutrino production efficiency but a lower best-fit baryonic loading. The predicted neutrino luminosity shows a positive correlation both with the observed flux of gigaelectronvolt gamma rays and with the predicted flux of megaelectronvolt gamma rays. We also estimate the diffuse neutrino flux from gamma-ray bla/ars by extrapolating the result to the
Fermi
population, and we show that it may be at the level of ~20% of the diffuse neutrino flux observed by IceCube, in agreement with current limits from stacking analyses. We discuss the implications of our results for future neutrino searches and suggest promising sources for potential detections.
Texas is estimated to harbor more than 2 million feral hogs, Sus scrofa. The increasing abundance of feral hogs throughout the United States is a testament to their ability to adapt to nearly any ...environment. We GPS-collared and tracked 16 feral hogs in the spring of 2015 and 2016 in the Texas Panhandle, United States. We determined home range and core area size using kernel density (KDE) and minimum convex polygon (MCP) estimators and selection of habitats by feral hogs in two field sites. Mean (±se) KDE home range and core area sizes were 9.73 ± 1.74 km2 and 1.31 ± 0.23 km2, respectively. Mean (±se) MCP home range and core area sizes were 15.13 ± 3.49 km2 and 3.14 ± 0.69 km2, respectively. Home range sizes were slightly larger but comparable to other home range sizes in Texas, and with home range and core area sizes larger for males than female. Feral hogs did not exhibit second-and-third order habitat selection at random (P < 0.005) in both field sites. Hogs selected for woodland and floodplain habitats over human developed areas. Feral hogs spent more time in agricultural habitats during crepuscular and nighttime periods and more time in natural habitats throughout the day. These results suggest management techniques in northern Texas need to be executed for the removal or deterrence of feral hogs in areas of cultivated crops, ideally before the planting period through the harvesting season.
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