ABSTRACT
Blazars research is one of the hot topics of contemporary extragalactic astrophysics. That is because these sources are the most abundant type of extragalactic γ-ray sources and are ...suspected to play a central role in multimessenger astrophysics. We have used Swift$\_$xrtproc, a tool to carry out an accurate spectral and photometric analysis of the Swift-XRT data of all blazars observed by Swift at least 50 times between December 2004 and the end of 2020. We present a database of X-ray spectra, best-fit parameter values, count rates and flux estimations in several energy bands of over 31 000 X-ray observations and single snapshots of 65 blazars. The results of the X-ray analysis have been combined with other multifrequency archival data to assemble the broad-band Spectral Energy Distributions (SEDs) and the long-term light curves of all sources in the sample. Our study shows that large X-ray luminosity variability on different time-scales is present in all objects. Spectral changes are also frequently observed with a ‘harder-when-brighter’ or ‘softer-when-brighter’ behaviour depending on the SED type of the blazars. The peak energy of the synchrotron component (νpeak) in the SED of HBL blazars, estimated from the log-parabolic shape of their X-ray spectra, also exhibits very large changes in the same source, spanning a range of over two orders of magnitude in Mrk421 and Mrk501, the objects with the best data sets in our sample.
At present, a variety of dark matter (DM) density profiles are available in the literature, able to fit the observed rotation velocity curves in galaxies. These distributions may be classified ...according to nature and mass of the DM candidate, and their estimation of the concentration of DM on halo scales, as well as through their central regions. Examples of these distributions are the (empiric) Einasto or isotropic, the (N-body-simulation-based) Navarro–Frenk–White (NFW), or the (elementary-particle-based) Ruffini–Argüelles–Rueda (RAR), among others. In this work, we calculate the cross-sections for the interaction between neutrinos coming from astrophysical sources and DM particles subject to some of these distributions. Furthermore, we explore the changes in the neutrino oscillation patterns due to the different DM profiles used to represent the environment. From the results of the calculations it is concluded that both the cross-section and the neutrino oscillation pattern depend on the features of each of the adopted models for the DM distributions. For the case of the NFW and isotropic DM distributions the expected effects at Earth, for neutrinos coming from an extragalactic source, are noticeable while in the case of the RAR distribution the effects are restricted to a narrow region around the galactic center.
In this paper, we present the analysis and results of a direct measurement of the cosmic-ray proton spectrum with the CALET instrument onboard the International Space Station, including the detailed ...assessment of systematic uncertainties. The observation period used in this analysis is from October 13, 2015 to August 31, 2018 (1054 days). We have achieved the very wide energy range necessary to carry out measurements of the spectrum from 50 GeV to 10 TeV covering, for the first time in space, with a single instrument the whole energy interval previously investigated in most cases in separate subranges by magnetic spectrometers (BESS-TeV, PAMELA, and AMS-02) and calorimetric instruments (ATIC, CREAM, and NUCLEON). The observed spectrum is consistent with AMS-02 but extends to nearly an order of magnitude higher energy, showing a very smooth transition of the power-law spectral index from -2.81±0.03 (50-500 GeV) neglecting solar modulation effects (or -2.87±0.06 including solar modulation effects in the lower energy region) to -2.56±0.04 (1-10 TeV), thereby confirming the existence of spectral hardening and providing evidence of a deviation from a single power law by more than 3σ.
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Extended results on the cosmic-ray electron + positron spectrum from 11 GeV to 4.8 TeV are presented based on observations with the Calorimetric Electron Telescope (CALET) on the International Space ...Station utilizing the data up to November 2017. The analysis uses the full detector acceptance at high energies, approximately doubling the statistics compared to the previous result. CALET is an all-calorimetric instrument with a total thickness of 30 X_{0} at normal incidence and fine imaging capability, designed to achieve large proton rejection and excellent energy resolution well into the TeV energy region. The observed energy spectrum in the region below 1 TeV shows good agreement with Alpha Magnetic Spectrometer (AMS-02) data. In the energy region below ∼300 GeV, CALET's spectral index is found to be consistent with the AMS-02, Fermi Large Area Telescope (Fermi-LAT), and Dark Matter Particle Explorer (DAMPE), while from 300 to 600 GeV the spectrum is significantly softer than the spectra from the latter two experiments. The absolute flux of CALET is consistent with other experiments at around a few tens of GeV. However, it is lower than those of DAMPE and Fermi-LAT with the difference increasing up to several hundred GeV. The observed energy spectrum above ∼1 TeV suggests a flux suppression consistent within the errors with the results of DAMPE, while CALET does not observe any significant evidence for a narrow spectral feature in the energy region around 1.4 TeV. Our measured all-electron flux, including statistical errors and a detailed breakdown of the systematic errors, is tabulated in the Supplemental Material in order to allow more refined spectral analyses based on our data.
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Neutrinos are produced in cosmic accelerators, like active galactic nuclei, blazars, supernova remnants and gamma-ray bursts (GRBs). On their way to the Earth they experience flavor oscillations. The ...interactions of the neutrinos coming from the source with other particles, e.g., intergalactic primordial neutrinos or heavy-mass right-handed neutrinos, on their way to the detector may transform the original wavepacket in pointer states. This phenomenon, known as decoherence, becomes important in the reconstruction of processes at the source. In this work, we study neutrino emission in short GRBs by adopting the Fireshell Model. We consider e−e+-pair annihilation as the main channel for neutrino production. We compare the properties of the neutrino flux with the characteristic photon signal produced once the transparency condition is reached. We study the effects of flavor oscillations and decoherence as neutrinos travel from the region near the black hole event horizon outward. We consider the source to be in thermal equilibrium and calculate energy distribution functions for electrons and neutrinos. To compute the effects of decoherence we use a Gaussian model. In this scenario, the emitted electron-neutrinos transform into pointer states consisting of 67.8% electron-neutrinos and 32.2% as a combination of mu and tau neutrinos. We found that decoherence plays an important role in the evolution of the neutrino wavepacket, leading to the detected pointer states on Earth.
Aims. Open Universe for Blazars is a set of high-transparency multi-frequency data products for blazar science, and the tools designed to generate them. Blazars are drawing growing interest following ...the consolidation of their position as the most abundant type of source in the extragalactic very high-energy γ-ray sky, and because of their status as prime candidate sources in the nascent field of multi-messenger astrophysics. As such, blazar astrophysics is becoming increasingly data driven, depending on the integration and combined analysis of large quantities of data from the entire span of observational astrophysics techniques. The project was therefore chosen as one of the pilot activities within the United Nations Open Universe Initiative, whose objective is to stimulate a large increase in the accessibility and ease of utilisation of space science data for the worldwide benefit of scientific research, education, capacity building, and citizen science. Methods. Our aim is to deliver innovative data science tools for multi-messenger astrophysics. In this work we report on a data analysis pipeline called Swift-DeepSky based on the Swift XRTDAS software and the XIMAGE package, encapsulated into a Docker container. Swift-DeepSky downloads and reads low-level data, generates higher level products, detects X-ray sources, and estimates several intensity and spectral parameters for each detection, thus facilitating the generation of complete and up-to-date science-ready catalogues from an entire space-mission data set. Results. As a first application of our innovative approach, we present the results of a detailed X-ray image analysis based on Swift-DeepSky that was run on all Swift-XRT observations including a known blazar, carried out during the first 14 years of operations of the Neil Gehrels Swift Observatory. Short exposures executed within one week of each other have been added to increase sensitivity, which ranges between ∼1 × 10−12 and ∼1 × 10−14 erg cm−2 s−1 (0.3–10.0 keV). After cleaning for problematic fields, the resulting database includes over 27 000 images integrated in different X-ray bands, and a catalogue, called 1OUSXB, that provides intensity and spectral information for 33 396 X-ray sources, 8896 of which are single or multiple detections of 2308 distinct blazars. All the results can be accessed online in a variety of ways, from the Open Universe portal through Virtual Observatory services, via the VOU-Blazar tool and the SSDC SED builder. One of the most innovative aspects of this work is that the results can be easily reproduced and extended by anyone using the Docker version of the Swift-DeepSky pipeline, which runs on Linux, Mac, and Windows machines, and does not require any specific experience in X-ray data analysis.
Early X-Ray Flares in GRBs Ruffini, R.; Wang, Y.; Aimuratov, Y. ...
Astrophysical journal/The Astrophysical journal,
01/2018, Volume:
852, Issue:
1
Journal Article
Peer reviewed
Open access
We analyze the early X-ray flares in the GRB "flare-plateau-afterglow" (FPA) phase observed by Swift-XRT. The FPA occurs only in one of the seven GRB subclasses: the binary-driven hypernovae (BdHNe). ...This subclass consists of long GRBs with a carbon-oxygen core and a neutron star (NS) binary companion as progenitors. The hypercritical accretion of the supernova (SN) ejecta onto the NS can lead to the gravitational collapse of the NS into a black hole. Consequently, one can observe a GRB emission with isotropic energy erg, as well as the associated GeV emission and the FPA phase. Previous work had shown that gamma-ray spikes in the prompt emission occur at cm with Lorentz Gamma factors . Using a novel data analysis, we show that the time of occurrence, duration, luminosity, and total energy of the X-ray flares correlate with Eiso. A crucial feature is the observation of thermal emission in the X-ray flares that we show occurs at radii ∼1012 cm with . These model-independent observations cannot be explained by the "fireball" model, which postulates synchrotron and inverse-Compton radiation from a single ultrarelativistic jetted emission extending from the prompt to the late afterglow and GeV emission phases. We show that in BdHNe a collision between the GRB and the SN ejecta occurs at 1010 cm, reaching transparency at ∼1012 cm with . The agreement between the thermal emission observations and these theoretically derived values validates our model and opens the possibility of testing each BdHN episode with the corresponding Lorentz Gamma factor.
In this Letter we make an estimate of the time delay between signals, recorded at detectors on Earth, of neutrinos and photons originated in a short gamma-ray burst. We describe the geometry and ...dynamics of the system according to the Fireshell model. The delay in the photon's arrival time is produced because the system is originally opaque to radiation; thus, the photons remain trapped and thermalize until the transparency condition is reached. We calculate the time interval between neutrino emission and photon emission in the black hole frame and transform it to the observer frame using Lorentz transformations. We obtain a difference in the arrival time at Earth of .
Theoretical and observational evidences for a two-fold classification of short bursts have been recently obtained: (1) short gamma-ray flashes (S-GRFs), with isotropic energy E iso < 10 52 erg and no ...black hole (BH) formation, and (2) authentic short gamma-ray bursts (S-GRBs), with isotropic energy E iso > 10 52 erg showing evidence of BH formation in the binary neutron star merging process. The signature for BH formation is the onset of high-energy (0.1-100 GeV) emission, coeval to the prompt emission, in all S-GRBs. No GeV emission is expected nor observed in S-GRFs. In this paper, we present two S-GRBs, GRB 081024B and GRB 140402A, in addition to the already identified S-GRBs, GRB 090227B, GRB 090510, and GRB 140619B. We also return to the absence of GeV emission in the S-GRB 090227B, at an angle of 71 ° from the Fermi-LAT boresight. All of the correctly identified S-GRBs correlate with high-energy emission, implying no significant presence of beaming in GeV emission. The existence of a common power-law behavior in the GeV luminosities, following the BH formation, when measured in the source rest frame, points to a commonality in the mass and spin of the newly formed BHs in all S-GRBs.
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