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C. Bigongiari

Publications and source records attributed to C. Bigongiari.

At least 109 records · Page 6Linked to original sources
arXiv2018

Periastron Observations of TeV Gamma-Ray Emission from a Binary System with a 50-year Period

We report on observations of the pulsar / Be star binary system PSR J2032+4127 / MT91 213 in the energy range between 100 GeV and 20 TeV with the VERITAS and MAGIC imaging atmospheric Cherenkov telescope arrays. The binary orbit has a period of approximately 50 years, with the most recent periastron occurring on 2017 November 13. Our observations span from 18 months prior to periastron to one month after. A new, point-like, gamma-ray source is detected, coincident with the location of PSR J2032+4127 / MT91 213. The gamma-ray light curve and spectrum are well-characterized over the periastron passage. The flux is variable over at least an order of magnitude, peaking at periastron, thus providing a firm association of the TeV source with the pulsar / Be star system. Observations prior to periastron show a cutoff in the spectrum at an energy around 0.5 TeV. This result adds a new member to the small population of known TeV binaries, and it identifies only the second source of this class in which the nature and properties of the compact object are firmly established. We compare the gamma-ray results with the light curve measured with the X-ray Telescope (XRT) on board the Neil Gehrels \textit{Swift} Observatory and with the predictions of recent theoretical models of the system. We conclude that significant revision of the models is required to explain the details of the emission we have observed, and we discuss the relationship between the binary system and the overlapping steady extended source, TeV J2032+4130.

astro-ph.HE↗
arXiv2018

Detection of persistent VHE gamma-ray emission from PKS 1510-089 by the MAGIC telescopes during low states between 2012 and 2017

PKS 1510-089 is a flat spectrum radio quasar strongly variable in the optical and GeV range. We search for low-state VHE gamma-ray emission from PKS 1510-089. We aim to characterize and model the source in a broad-band context, which would provide a baseline over which high states and flares could be better understood. We use daily binned Fermi-LAT flux measurements of PKS 1510-089 to characterize the GeV emission and select the observation periods of MAGIC during low state of activity. For the selected times we compute the average radio, IR, optical, UV, X-ray and gamma-ray emission to construct a low-state spectral energy distribution of the source. The broadband emission is modelled within an External Compton scenario with a stationary emission region through which plasma and magnetic field are flowing. We perform also the emission-model-independent calculations of the maximum absorption in the broad line region (BLR) using two different models. Results. The MAGIC telescopes collected 75 hrs of data during times when the Fermi-LAT flux measured above 1 GeV was below 3x10-8cm-2s-1, which is the threshold adopted for the definition of a low gamma-ray activity state. The data show a strongly significant (9.5σ) VHE gamma-ray emission at the level of (4.27+-0.61stat)x10-12cm-2s-1 above 150GeV, a factor 80 smaller than the highest flare observed so far from this object. Despite the lower flux, the spectral shape is consistent with earlier detections in the VHE band. The broad-band emission is compatible with the EC scenario assuming a large emission region located beyond the BLR. For the first time the gamma-ray data allow us to place a limit on the location of the emission region during a low gamma-ray state of a FSRQ. For the used model of the BLR, the 95% C.L. on the location of the emission region allows us to place it at the distance >74% of the outer radius of the BLR.

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arXiv2018

Constraining very-high-energy and optical emission from FRB 121102 with the MAGIC telescopes

Fast radio bursts (FRBs) are bright flashes observed typically at GHz frequencies with millisecond duration, whose origin is likely extragalactic. Their nature remains mysterious, motivating searches for counterparts at other wavelengths. FRB 121102 is so far the only source known to repeatedly emit FRBs and is associated with a host galaxy at redshift $z \simeq 0.193$. We conducted simultaneous observations of FRB 121102 with the Arecibo and MAGIC telescopes during several epochs in 2016--2017. This allowed searches for millisecond-timescale burst emission in very-high-energy (VHE) gamma rays as well as the optical band. While a total of five FRBs were detected during these observations, no VHE emission was detected, neither of a persistent nature nor burst-like associated with the FRBs. The average integral flux upper limits above 100 GeV at 95% confidence level are $6.6 \times 10^{-12}~\mathrm{photons\ cm^{-2}\ s^{-1}}$ (corresponding to luminosity $L_{\rm VHE} \lesssim 10^{45}~\mathrm{erg\ s^{-1}}$) over the entire observation period, and $1.2 \times 10^{-7}~ \mathrm{photons\ cm^{-2}\ s^{-1}}$ ($L_{\rm VHE} \lesssim 10^{49}~\mathrm{erg\ s^{-1}}$) over the total duration of the five FRBs. We constrain the optical U-band flux to be below 8.6 mJy at 5-$σ$ level for 1-ms intervals around the FRB arrival times. A bright burst with U-band flux $29~\mathrm{mJy}$ and duration $\sim 12$ ms was detected 4.3 s before the arrival of one FRB. However, the probability of spuriously detecting such a signal within the sampled time space is 1.5% (2.2 $σ$, post-trial), i.e. consistent with the expected background. We discuss the implications of the obtained upper limits for constraining FRB models.

astro-ph.HE↗
arXiv2018

Constraining Dark Matter lifetime with a deep gamma-ray survey of the Perseus Galaxy Cluster with MAGIC

Clusters of galaxies are the largest known gravitationally bound structures in the Universe, with masses around $10^{15}\ M_\odot$, most of it in the form of dark matter. The ground-based Imaging Atmospheric Cherenkov Telescope MAGIC made a deep survey of the Perseus cluster of galaxies using almost 400 h of data recorded between 2009 and 2017. This is the deepest observational campaign so far on a cluster of galaxies in the very high energy range. We search for gamma-ray signals from dark matter particles in the mass range between 200 GeV and 200 TeV decaying into standard model pairs. We apply an analysis optimized for the spectral and morphological features expected from dark matter decays and find no evidence of decaying dark matter. From this, we conclude that dark matter particles have a decay lifetime longer than $\sim10^{26}$~s in all considered channels. Our results improve previous lower limits found by MAGIC and represent the strongest limits on decaying dark matter particles from ground-based gamma-ray instruments.

astro-ph.HE↗
arXiv2018

The blazar TXS 0506+056 associated with a high-energy neutrino: insights into extragalactic jets and cosmic ray acceleration

A neutrino with energy of $\sim$290 TeV, IceCube-170922A, was detected in coincidence with the BL Lac object TXS~0506+056 during enhanced gamma-ray activity, with chance coincidence being rejected at $\sim 3σ$ level. We monitored the object in the very-high-energy (VHE) band with the MAGIC telescopes for $\sim$41 hours from 1.3 to 40.4 days after the neutrino detection. Day-timescale variability is clearly resolved. We interpret the quasi-simultaneous neutrino and broadband electromagnetic observations with a novel one-zone lepto-hadronic model, based on interactions of electrons and protons co-accelerated in the jet with external photons originating from a slow-moving plasma sheath surrounding the faster jet spine. We can reproduce the multiwavelength spectra of TXS 0506+056 with neutrino rate and energy compatible with IceCube-170922A, and with plausible values for the jet power of $\sim 10^{45} - 4 \times 10^{46} {\rm erg \ s^{-1}}$. The steep spectrum observed by MAGIC is concordant with internal $γγ$ absorption above a few tens of GeV entailed by photohadronic production of a $\sim$290 TeV neutrino, corroborating a genuine connection between the multi-messenger signals. In contrast to previous predictions of predominantly hadronic emission from neutrino sources, the gamma-rays can be mostly ascribed to inverse Compton up-scattering of external photons by accelerated electrons. The X-ray and VHE bands provide crucial constraints on the emission from both accelerated electrons and protons. We infer that the maximum energy of protons in the jet co-moving frame can be in the range $\sim 10^{14}$ to $10^{18}$ eV.

astro-ph.HE↗
arXiv2018

The broad-band properties of the intermediate synchrotron peaked BL Lac S2 0109+22 from radio to VHE gamma rays

The MAGIC telescopes observed S2 0109+22 in 2015 July during its flaring activity in high energy gamma rays observed by Fermi-LAT. We analyse the MAGIC data to characterise the very high energy (VHE) gamma-ray emission of S2 0109+22, which belongs to the subclass of intermediate synchrotron peak (ISP) BL Lac objects. We study the multi-frequency emission in order to investigate the source classification. Finally, we compare the source long-term behaviour to other VHE gamma-ray emitting (TeV) blazars. We performed a temporal and spectral analysis of the data centred around the MAGIC interval of observation (MJD 57225-57231). Long-term radio and optical data have also been investigated using the discrete correlation function. The redshift of the source is estimated through optical host-galaxy imaging and also using the amount of VHE gamma-ray absorption. The quasi-simultaneous multi-frequency spectral energy distribution (SED) is modelled with the conventional one-zone synchrotron self-Compton (SSC) model. MAGIC observations resulted in the detection of the source at a significance level of $5.3\,σ$. The VHE gamma-ray emission of S2 0109+22 is variable on a daily time scale. VHE gamma-ray luminosity of the source is lower than the average of TeV BL Lacs. The optical polarization, and long-term optical/radio behaviour of the source are different from the general population of TeV blazars. All these findings agree with the classification of the source as an ISP BL Lac object. We estimate the source redshift as $z = 0.36 \pm 0.07$. The SSC parameters describing the SED are rather typical for blazars.

astro-ph.HE↗
arXiv2018

Gamma-ray flaring activity of NGC 1275 in 2016-2017 measured by MAGIC

We report on the detection of flaring activity from the Fanaroff-Riley I radio galaxy NGC 1275 in very-high-energy (VHE, E $>$ 100 GeV) gamma rays with the MAGIC telescopes. Observations were performed between 2016 September and 2017 February as part of a monitoring program. The brightest outburst with $\sim1.5$ times the Crab Nebula flux above 100 GeV (C.U.) was observed during the night between 2016 December 31 and 2017 January 1 (fifty times higher than the mean previously measured in two observational campaigns between 2009 and 2011). Significant variability of the day-by-day light curve was measured, the shortest flux-doubling time-scales was found to be of $(611\pm101)$ min. The combined spectrum of the MAGIC data during the strongest flare state and simultaneous data from the Fermi-LAT around 2017 January 1 follows a power-law with an exponential cutoff at the energy $(492\pm35)$ GeV. Simultaneous optical flux density measurements in the R-band obtained with the KVA telescope are also presented and the correlation between the optical and gamma-ray emission is investigated. Due to possible internal pair-production, the fast flux variability constrains the Doppler factor to values which are inconsistent with a large viewing angle as observed in the radio band. We investigate different scenarios for the explanation of fast gamma-ray variability, namely emission from: magnetospheric gaps, relativistic blobs propagating in the jet (mini-jets) or external cloud (or star) entering the jet. We find that the only plausible model to account for the luminosities here observed would be the production of gamma rays in a magnetospheric gap around the central black hole only in the eventuality of an enhancement of the magnetic field threading the hole from its equipartition value with the gas pressure in the accretion flow.

astro-ph.HE↗
arXiv2018

Science with the Cherenkov Telescope Array

The Cherenkov Telescope Array, CTA, will be the major global observatory for very high energy gamma-ray astronomy over the next decade and beyond. The scientific potential of CTA is extremely broad: from understanding the role of relativistic cosmic particles to the search for dark matter. CTA is an explorer of the extreme universe, probing environments from the immediate neighbourhood of black holes to cosmic voids on the largest scales. Covering a huge range in photon energy from 20 GeV to 300 TeV, CTA will improve on all aspects of performance with respect to current instruments. The observatory will operate arrays on sites in both hemispheres to provide full sky coverage and will hence maximize the potential for the rarest phenomena such as very nearby supernovae, gamma-ray bursts or gravitational wave transients. With 99 telescopes on the southern site and 19 telescopes on the northern site, flexible operation will be possible, with sub-arrays available for specific tasks. CTA will have important synergies with many of the new generation of major astronomical and astroparticle observatories. Multi-wavelength and multi-messenger approaches combining CTA data with those from other instruments will lead to a deeper understanding of the broad-band non-thermal properties of target sources. The CTA Observatory will be operated as an open, proposal-driven observatory, with all data available on a public archive after a pre-defined proprietary period. Scientists from institutions worldwide have combined together to form the CTA Consortium. This Consortium has prepared a proposal for a Core Programme of highly motivated observations. The programme, encompassing approximately 40% of the available observing time over the first ten years of CTA operation, is made up of individual Key Science Projects (KSPs), which are presented in this document.

astro-ph.IM↗
arXiv2017

ASTRI SST-2M prototype and mini-array simulation chain, data reduction software, and archive in the framework of the Cherenkov Telescope Array

The Cherenkov Telescope Array (CTA) is a worldwide project aimed at building the next-generation ground-based gamma-ray observatory. Within the CTA project, the Italian National Institute for Astrophysics (INAF) is developing an end-to-end prototype of the CTA Small-Size Telescopes with a dual-mirror (SST-2M) Schwarzschild-Couder configuration. The prototype, named ASTRI SST-2M, is located at the INAF "M.C. Fracastoro" observing station in Serra La Nave (Mt. Etna, Sicily) and is currently in the scientific and performance validation phase. A mini-array of (at least) nine ASTRI telescopes has been then proposed to be deployed at the Southern CTA site, by means of a collaborative effort carried out by institutes from Italy, Brazil, and South-Africa. The CTA/ASTRI team is developing an end-to-end software package for the reduction of the raw data acquired with both ASTRI SST-2M prototype and mini-array, with the aim of actively contributing to the global ongoing activities for the official data handling system of the CTA observatory. The group is also undertaking a massive Monte Carlo simulation data production using the detector Monte Carlo software adopted by the CTA consortium. Simulated data are being used to validate the simulation chain and evaluate the ASTRI SST-2M prototype and mini-array performance. Both activities are also carried out in the framework of the European H2020-ASTERICS (Astronomy ESFRI and Research Infrastructure Cluster) project. A data archiving system, for both ASTRI SST-2M prototype and mini-array, has been also developed by the CTA/ASTRI team, as a testbed for the scientific archive of CTA. In this contribution, we present the main components of the ASTRI data handling systems and report the status of their development.

astro-ph.IM↗
arXiv2017

Prospects for CTA observations of the young SNR RX J1713.7-3946

We perform simulations for future Cherenkov Telescope Array (CTA) observations of RX~J1713.7$-$3946, a young supernova remnant (SNR) and one of the brightest sources ever discovered in very-high-energy (VHE) gamma rays. Special attention is paid to explore possible spatial (anti-)correlations of gamma rays with emission at other wavelengths, in particular X-rays and CO/H{\sc i} emission. We present a series of simulated images of RX J1713.7$-$3946 for CTA based on a set of observationally motivated models for the gamma-ray emission. In these models, VHE gamma rays produced by high-energy electrons are assumed to trace the non-thermal X-ray emission observed by {\it XMM-Newton}, whereas those originating from relativistic protons delineate the local gas distributions. The local atomic and molecular gas distributions are deduced by the NANTEN team from CO and H{\sc i} observations. Our primary goal is to show how one can distinguish the emission mechanism(s) of the gamma rays (i.e., hadronic vs leptonic, or a mixture of the two) through information provided by their spatial distribution, spectra, and time variation. This work is the first attempt to quantitatively evaluate the capabilities of CTA to achieve various proposed scientific goals by observing this important cosmic particle accelerator.

astro-ph.HE↗
arXiv2016

Prospects for PWNe and SNRs science with the ASTRI mini-array of pre-production small-sized telescopes of the Cherenkov Telescope Array

The development and construction of the Cherenkov Telescope Array (CTA) opens up new opportunities for the study of very high energy (VHE, E>100 GeV) sources. As a part of CTA, the ASTRI project, led by INAF, has one of the main goals to develop one of the mini-arrays of CTA pre-production telescopes, proposed to be installed at the CTA southern site. Thanks to the innovative dual-mirror optical design of its small-sized telescopes, the ASTRI mini-array will be characterized by a large field of view, an excellent angular resolutioerrorn and a good sensitivity up to energies of several tens of TeV. Pulsar wind nebulae, along with Supernova Remnants, are among the most abundant sources that will be identified and investigated, with the ultimate goal to move significantly closer to an understanding of the origin of cosmic rays (CR). As part of the ongoing effort to investigate the scientific capabilities for both CTA as a whole and the ASTRI mini-array, we performed simulations of the Vela X region. We simulated its extended VHE gamma-ray emission using the results of the detailed H.E.S.S. analysis of this source. We estimated the resolving capabilities of the diffuse emission and the detection significance of the pulsar with both CTA as a whole and the ASTRI mini-array. Moreover with these instruments it will be possible to observe the high-energy end of SNRs spectrum, searching for particles with energies near the cosmic-rays "knee" (E~10^15 eV). We simulated a set of ASTRI mini-array observations for one young and an evolved SNRs in order to test the capabilities of this instrument to discover and study PeVatrons on the Galactic plane.

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arXiv2014

A Search for Time Dependent Neutrino Emission from Microquasars with the ANTARES Telescope

Results are presented on a search for neutrino emission from a sample of six microquasars, based on the data collected by the ANTARES neutrino telescope between 2007 and 2010. By means of appropriate time cuts, the neutrino search has been restricted to the periods when the acceleration of relativistic jets was taking place at the microquasars under study. The time cuts have been chosen using the information from the X-ray telescopes RXTE/ASM and Swift/BAT, and, in one case, the gamma-ray telescope Fermi/LAT. Since none of the searches has produced a statistically significant signal, upper limits on the neutrino fluences are derived and compared to the predictions from theoretical models.

astro-ph.HE↗
arXiv2013

A Search for Neutrino Emission from the Fermi Bubbles with the ANTARES Telescope

Analysis of the Fermi-LAT data has revealed two extended structures above and below the Galactic Centre emitting gamma rays with a hard spectrum, the so-called Fermi bubbles. Hadronic models attempting to explain the origin of the Fermi bubbles predict the emission of high-energy neutrinos and gamma rays with similar fluxes. The ANTARES detector, a neutrino telescope located in the Mediterranean Sea, has a good visibility to the Fermi bubble regions. Using data collected from 2008 to 2011 no statistically significant excess of events is observed and therefore upper limits on the neutrino flux in TeV range from the Fermi bubbles are derived for various assumed energy cutoffs of the source.

astro-ph.HE↗
arXiv2013

Search for muon neutrinos from gamma-ray bursts with the ANTARES neutrino telescope using 2008 to 2011 data

A search for muon neutrinos in coincidence with gamma-ray bursts with the ANTARES neutrino detector using data from the end of 2007 to 2011 is performed. Expected neutrino fluxes are calculated for each burst individually. The most recent numerical calculations of the spectra using the NeuCosmA code are employed, which include Monte Carlo simulations of the full underlying photohadronic interaction processes. The discovery probability for a selection of 296 gamma-ray bursts in the given period is optimised using an extended maximum-likelihood strategy. No significant excess over background is found in the data, and 90% confidence level upper limits are placed on the total expected flux according to the model.

astro-ph.HE↗
arXiv2013

First Search for Dark Matter Annihilation in the Sun Using the ANTARES Neutrino Telescope

A search for high-energy neutrinos coming from the direction of the Sun has been performed using the data recorded by the ANTARES neutrino telescope during 2007 and 2008. The neutrino selection criteria have been chosen to maximize the selection of possible signals produced by the self-annihilation of weakly interacting massive particles accumulated in the centre of the Sun with respect to the atmospheric background. After data unblinding, the number of neutrinos observed towards the Sun was found to be compatible with background expectations. The $90\%$ CL upper limits in terms of spin-dependent and spin-independent WIMP-proton cross-sections are derived and compared to predictions of two supersymmetric models, CMSSM and MSSM-7. The ANTARES limits are competitive with those obtained by other neutrino observatories and are more stringent than those obtained by direct search experiments for the spin-dependent WIMP-proton cross-section.

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