Signal estimation in the presence of background noise is a common problem in several scientific disciplines. An "on/off" measurement is performed when the background itself is not known, being ...estimated from a background control sample. The "frequentist" and Bayesian approaches for signal estimation in on/off measurements are reviewed and compared, focusing on the weakness of the former and on the advantages of the latter in correctly addressing the Poissonian nature of the problem. In this work, we devise a novel reconstruction method, Bayesian analysis including single-event likelihoods (dubbed BASiL), for estimating the signal rate based on the Bayesian formalism. It uses information on event-by-event individual parameters and their distribution for the signal and background population. Events are thereby weighted according to their likelihood of being a signal or a background event and background suppression can be achieved without performing fixed fiducial cuts. Throughout the work, we maintain a general notation that allows us to apply the method generically and provides a performance test using real data and simulations of observations with the MAGIC telescopes, as a demonstration of the performance for Cherenkov telescopes. BASiL allows one to estimate the signal more precisely, avoiding loss of exposure due to signal extraction cuts. We expect its applicability to be straightforward in similar cases.
MAGIC detection of GRB 201216C at z = 1.1 Acciari, V A; Agudo, I; Aniello, T ...
Monthly notices of the Royal Astronomical Society,
01/2024, Letnik:
527, Številka:
3
Journal Article
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ABSTRACT
Gamma-ray bursts (GRBs) are explosive transient events occurring at cosmological distances, releasing a large amount of energy as electromagnetic radiation over several energy bands. We ...report the detection of the long GRB 201216C by the MAGIC telescopes. The source is located at z = 1.1 and thus it is the farthest one detected at very high energies. The emission above 70 GeV of GRB 201216C is modelled together with multiwavelength data within a synchrotron and synchrotron self-Compton (SSC) scenario. We find that SSC can explain the broad-band data well from the optical to the very-high-energy band. For the late-time radio data, a different component is needed to account for the observed emission. Differently from previous GRBs detected in the very-high-energy range, the model for GRB 201216C strongly favours a wind-like medium. The model parameters have values similar to those found in past studies of the afterglows of GRBs detected up to GeV energies.
ABSTRACT
In recent years, a new generation of optical intensity interferometers has emerged, leveraging the existing infrastructure of Imaging Atmospheric Cherenkov Telescopes (IACTs). The MAGIC ...telescopes host the MAGIC-SII system (Stellar Intensity Interferometer), implemented to investigate the feasibility and potential of this technique on IACTs. After the first successful measurements in 2019, the system was upgraded and now features a real-time, dead-time-free, 4-channel, GPU-based correlator. These hardware modifications allow seamless transitions between MAGIC’s standard very-high-energy gamma-ray observations and optical interferometry measurements within seconds. We establish the feasibility and potential of employing IACTs as competitive optical Intensity Interferometers with minimal hardware adjustments. The measurement of a total of 22 stellar diameters are reported, 9 corresponding to reference stars with previous comparable measurements, and 13 with no prior measurements. A prospective implementation involving telescopes from the forthcoming Cherenkov Telescope Array Observatory’s Northern hemisphere array, such as the first prototype of its Large-Sized Telescopes, LST-1, is technically viable. This integration would significantly enhance the sensitivity of the current system and broaden the UV-plane coverage. This advancement would enable the system to achieve competitive sensitivity with the current generation of long-baseline optical interferometers over blue wavelengths.
Milky Way dwarf spheroidal galaxies (dSphs) are among the best candidates to search for signals of dark matter annihilation with Imaging Atmospheric Cherenkov Telescopes, given their high ...mass-to-light ratios and the fact that they are free of astrophysical gamma-ray emitting sources. Since 2011, MAGIC has performed a multi-year observation program in search for Weakly Interacting Massive Particles (WIMPs) in dSphs. Results on the observations of Segue 1 and Ursa Major II dSphs have already been published and include some of the most stringent upper limits (ULs) on the velocity-averaged cross-section 〈σannv〉 of WIMP annihilation from observations of dSphs. In this work, we report on the analyses of 52.1h of data of Draco dSph and 49.5h of Coma Berenices dSph observed with the MAGIC telescopes in 2018 and in 2019 respectively. No hint of a signal has been detected from either of these targets and new constraints on the 〈σannv〉 of WIMP candidates have been derived. In order to improve the sensitivity of the search and reduce the effect of the systematic uncertainties due to the J-factor estimates, we have combined the data of all dSphs observed with the MAGIC telescopes. Using 354.3h of dSphs good quality data, 95% CL ULs on 〈σannv〉 have been obtained for 9 annihilation channels. For most of the channels, these results reach values of the order of 10−24cm3/s at ∼1TeV and are the most stringent limits obtained with the MAGIC telescopes so far.
Electronic resources are increasingly becoming essential in students' learning primarily due to their availability and ease of access over the Internet. Higher education institutions have to ...understand the Internet information-seeking behaviors of students and how they perceive electronic resources in order to effectively fulfill their mission of equipping students with relevant and contemporary knowledge and skills. The influence of four background variables (gender, level of study, enrollment status, and field of study) was examined in the analysis of data from 900 students at one Croatian university. The results show that students mostly use Wikipedia and similar online resources, as well as university websites, including websites of university libraries. The level and field of study are strong predictors of differences in the frequency of use of certain Internet sources. Factor analysis revealed four factors: tendency to use, advantages of using, incentives and reasons for using, and prerequisites for using electronic resources. These factors represent the underlying constructs by which students' perceptions of electronic resources can be classified. The findings further indicate that students only slightly prefer electronic over printed resources, although they highly value the benefits of the use of electronic formats. In addition, it has been revealed that students believe that they are well equipped and possess competencies for the effective use of electronic resources. Differences based on the factors have been largely confirmed with regard to gender and field of study, but not to the level of study and enrollment status. This study extends findings from previous research by placing emphasis on examining the differences, especially at the latent level, between certain groups of students.
•Students mostly use Wikipedia and similar Internet sources as well as university websites.•Level and field of study are strong predictors of differences in the frequency of use.•Students slightly prefer electronic over printed resources.•Four factors determine students' perceptions of electronic resources.•Given these factors, differences with regard to gender and field of study have been confirmed.
Axion-like particles (ALPs) are pseudo-Nambu-Goldstone bosons that emerge in various theories beyond the standard model. These particles can interact with high-energy photons in external magnetic ...fields, influencing the observed gamma-ray spectrum. This study analyzes 41.3 hrs of observational data from the Perseus Galaxy Cluster collected with the MAGIC telescopes. We focused on the spectra the radio galaxy in the center of the cluster: NGC 1275. By modeling the magnetic field surrounding this target, we searched for spectral indications of ALP presence. Despite finding no statistical evidence of ALP signatures, we were able to exclude ALP models in the sub-micro electronvolt range. Our analysis improved upon previous work by calculating the full likelihood and statistical coverage for all considered models across the parameter space. Consequently, we achieved the most stringent limits to date for ALP masses around 50 neV, with cross sections down to \(g_{a\gamma} = 3 \times 10^{-12}\) GeV\(^{-1}\).
Monthly Notices of the Royal Astronomical Society, Volume 527,
Issue 3, January 2024, Pages 5856-5867 Gamma-ray bursts (GRBs) are explosive transient events occurring at
cosmological distances, ...releasing a large amount of energy as electromagnetic
radiation over several energy bands. We report the detection of the long
GRB~201216C by the MAGIC telescopes. The source is located at $z=1.1$ and thus
it is the farthest one detected at very high energies. The emission above
\SI{70}{\GeV} of GRB~201216C is modelled together with multi-wavelength data
within a synchrotron and synchrotron-self Compton (SSC) scenario. We find that
SSC can explain the broadband data well from the optical to the
very-high-energy band. For the late-time radio data, a different component is
needed to account for the observed emission. Differently from previous GRBs
detected in the very-high-energy range, the model for GRB~201216C strongly
favors a wind-like medium. The model parameters have values similar to those
found in past studies of the afterglows of GRBs detected up to GeV energies.
Aims. LST-1, the prototype of the Large-Sized Telescope for the upcoming Cherenkov Telescope Array Observatory, is concluding its commissioning in Observatorio del Roque de los Muchachos on the ...island of La Palma. The proximity of LST-1 (Large-Sized Telescope 1) to the two MAGIC (Major Atmospheric Gamma Imaging Cherenkov) telescopes permits observations of the same gamma-ray events with both systems. Methods. We describe the joint LST-1+MAGIC analysis pipeline and use simultaneous Crab Nebula observations and Monte Carlo simulations to assess the performance of the three-telescope system. The addition of the LST-1 telescope allows the recovery of events in which one of the MAGIC images is too dim to survive analysis quality cuts. Results. Thanks to the resulting increase in the collection area and stronger background rejection, we find a significant improvement in sensitivity, allowing the detection of 30% weaker fluxes in the energy range between 200 GeV and 3 TeV. The spectrum of the Crab Nebula, reconstructed in the energy range ~60 GeV to ~10 TeV, is in agreement with previous measurements.
Line-like features in TeV \(\gamma\)-rays constitute a ''smoking gun'' for TeV-scale particle dark matter and new physics. Probing the Galactic Center region with ground-based Cherenkov telescopes ...enables the search for TeV spectral features in immediate association with a dense dark matter reservoir at a sensitivity out of reach for satellite \(\gamma\)-ray detectors, and direct detection and collider experiments. We report on 223 hours of observations of the Galactic Center region with the MAGIC stereoscopic telescope system reaching \(\gamma\)-ray energies up to 100 TeV. We improved the sensitivity to spectral lines at high energies using large-zenith-angle observations and a novel background modeling method within a maximum-likelihood analysis in the energy domain. No line-like spectral feature is found in our analysis. Therefore, we constrain the cross section for dark matter annihilation into two photons to \(\langle \sigma v \rangle \lesssim 5 \times 10^{-28}\,\mathrm{cm^3\,s^{-1}}\) at 1 TeV and \(\langle \sigma v \rangle \lesssim 1 \times 10^{-25}\,\mathrm{cm^3\,s^{-1}}\) at 100 TeV, achieving the best limits to date for a dark matter mass above 20 TeV and a cuspy dark matter profile at the Galactic Center. Finally, we use the derived limits for both cuspy and cored dark matter profiles to constrain supersymmetric wino models.
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