DSpace Repository :: Browsing by Author "Santander, Marcos"

Browsing by Author "Santander, Marcos"

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Constraints on high-energy neutrino emission from SN 2008D
(EDP Sciences, 2011-01-20) Santander, Marcos; University of Alabama Tuscaloosa
SN 2008D, a core collapse supernova at a distance of 27 Mpc, was serendipitously discovered by the Swift satellite through an associated X-ray flash. Core collapse supernovae have been observed in association with long gamma-ray bursts and X-ray flashes and a physical connection is widely assumed. This connection could imply that some core collapse supernovae possess mildly relativistic jets in which high-energy neutrinos are produced through proton-proton collisions. The predicted neutrino spectra would be detectable by Cherenkov neutrino detectors like IceCube. A search for a neutrino signal in temporal and spatial correlation with the observed X-ray flash of SN 2008D was conducted using data taken in 2007–2008 with 22 strings of the IceCube detector. Events were selected based on a boosted decision tree classifier trained with simulated signal and experimental background data. The classifier was optimized to the position and a “soft jet” neutrino spectrum assumed for SN 2008D. Using three search windows placed around the X-ray peak, emission time scales from 100–10 000 s were probed. No events passing the cuts were observed in agreement with the signal expectation of 0.13 events. Upper limits on the muon neutrino flux from core collapse supernovae were derived for different emission time scales and the principal model parameters were constrained. While no meaningful limits can be given in the case of an isotropic neutrino emission, the parameter space for a jetted emission can be constrained. Future analyses with the full 86 string IceCube detector could detect up to ~100 events for a core-collapse supernova at 10 Mpc according to the soft jet model.
Constraints on the extremely-high energy cosmic neutrino flux with the IceCube 2008-2009 data
(American Physical Society, 2011-05-24) Santander, Marcos; University of Alabama Tuscaloosa
We report on a search for extremely-high energy neutrinos with energies greater than 10⁶ GeV using the data taken with the IceCube detector at the South Pole. The data was collected between April 2008 and May 2009 with the half-completed IceCube array. The absence of signal candidate events in the sample of 333.5 days of live time significantly improves model-independent limits from previous searches and allows to place a limit on the diffuse flux of cosmic neutrinos with an E⁻² spectrum in the energy range 2.0×10⁶−6.3×10⁹ GeV to a level of E²ϕ≤3.6×10⁻⁸ GeV cm⁻² sec⁻¹ sr⁻¹.
Construction of a Medium-Sized Schwarzschild-Couder Telescope for the Cherenkov Telescope Array: Implementation of the Cherenkov-Camera Data Acquisition System
(2016-08-18) Santander, Marcos; University of Alabama Tuscaloosa
A medium-sized Schwarzchild-Couder Telescope (SCT) is being developed as a possible extension for the Cherenkov Telescope Array (CTA). The Cherenkov camera of the telescope is designed to have 11328 silicon photomultiplier pixels capable of capturing high-resolution images of air showers in the atmosphere. The combination of the large number of pixels and the high trigger rate (> 5 kHz) expected for this telescope results in a multi-Gbps data throughput. This sets challenging requirements on the design and performance of a data acquisition system for processing and storing this data. A prototype SCT (pSCT) with a partial camera containing 1600 pixels, covering a field of view of 2.5 x 2.5 square degrees, is being assembled at the F.L. Whipple Observatory. We present the design and current status of the SCT data acquisition system.
Determining neutrino oscillation parameters from atmospheric muon neutrino disappearance with three years of IceCube DeepCore data
(American Physical Society, 2015-04-07) Santander, Marcos; University of Alabama Tuscaloosa
We present a measurement of neutrino oscillations via atmospheric muon neutrino disappearance with three years of data of the completed IceCube neutrino detector. DeepCore, a region of denser IceCube instrumentation, enables the detection and reconstruction of atmospheric muon neutrinos between 10 and 100 GeV, where a strong disappearance signal is expected. The IceCube detector volume surrounding DeepCore is used as a veto region to suppress the atmospheric muon background. Neutrino events are selected where the detected Cherenkov photons of the secondary particles minimally scatter, and the neutrino energy and arrival direction are reconstructed. Both variables are used to obtain the neutrino oscillation parameters from the data, with the best fit given by Δm^2_32 = 2.72^+0.19_-0.20 × 10^-3 eV^2 and sin^2 θ_23 = 0.53^+0.09_-0.12 (normal mass ordering assumed). The results are compatible, and comparable in precision, to those of dedicated oscillation experiments.
The Exceptional TeV Flaring Activity of the Blazar 1ES 1959+650 in 2015 and 2016 as Observed with VERITAS
(2018-08-03) Santander, Marcos; University of Alabama Tuscaloosa
The high-synchrotron-peaked blazar 1ES 1959+650 was among the first extragalactic sources detected in the very high energy gamma ray band (VHE, E > 100 GeV). In October 2015, the source entered an extended period of activity that continued through July 2016, during which several strong VHE flares were observed. This flaring activity in the TeV band was accompanied by a strong increase in the optical, X-ray, and GeV gamma-ray flux of the source, surpassing its brightest recorded flux states. The VERITAS telescope array performed observations of 1ES 1959+650 between October 2015 and June 2016, and detected the source multiple times at a flux higher than the Crab nebula flux in the TeV band, representing the brightest flares of this object since 2002. We here present results from the analysis of 32 hours of VERITAS observations obtained during this period and as well as a contemporaneous multi-wavelength observations in the optical, X-ray, and GeV gamma-ray bands.
Extreme HBL behavior of Markarian 501 during 2012
(EDP Sciences, 2018-12-14) Santander, Marcos; University of Alabama Tuscaloosa
Aims. We aim to characterize the multiwavelength emission from Markarian 501 (Mrk 501), quantify the energy-dependent variability, study the potential multiband correlations, and describe the temporal evolution of the broadband emission within leptonic theoretical scenarios. Methods. We organized a multiwavelength campaign to take place between March and July of 2012. Excellent temporal coverage was obtained with more than 25 instruments, including the MAGIC, FACT and VERITAS Cherenkov telescopes, the instruments on board the Swift and Fermi spacecraft, and the telescopes operated by the GASP-WEBT collaboration. Results. Mrk 501 showed a very high energy (VHE) gamma-ray flux above 0.2 TeV of ∼0.5 times the Crab Nebula flux (CU) for most of the campaign. The highest activity occurred on 2012 June 9, when the VHE flux was ∼3 CU, and the peak of the high-energy spectral component was found to be at ∼2 TeV. Both the X-ray and VHE gamma-ray spectral slopes were measured to be extremely hard, with spectral indices < 2 during most of the observing campaign, regardless of the X-ray and VHE flux. This study reports the hardest Mrk 501 VHE spectra measured to date. The fractional variability was found to increase with energy, with the highest variability occurring at VHE. Using the complete data set, we found correlation between the X-ray and VHE bands; however, if the June 9 flare is excluded, the correlation disappears (significance < 3σ) despite the existence of substantial variability in the X-ray and VHE bands throughout the campaign. Conclusions. The unprecedentedly hard X-ray and VHE spectra measured imply that their low- and high-energy components peaked above 5 keV and 0.5 TeV, respectively, during a large fraction of the observing campaign, and hence that Mrk 501 behaved like an extreme high-frequency-peaked blazar (EHBL) throughout the 2012 observing season. This suggests that being an EHBL may not be a permanent characteristic of a blazar, but rather a state which may change over time. The data set acquired shows that the broadband spectral energy distribution (SED) of Mrk 501, and its transient evolution, is very complex, requiring, within the framework of synchrotron self-Compton (SSC) models, various emission regions for a satisfactory description. Nevertheless the one-zone SSC scenario can successfully describe the segments of the SED where most energy is emitted, with a significant correlation between the electron energy density and the VHE gamma-ray activity, suggesting that most of the variability may be explained by the injection of high-energy electrons. The one-zone SSC scenario used reproduces the behavior seen between the measured X-ray and VHE gamma-ray fluxes, and predicts that the correlation becomes stronger with increasing energy of the X-rays.
Finding fossil galaxy system progenitors using strong gravitational lensing
(University of Alabama Libraries, 2018) Johnson, Lucas Edward; Irwin, Jimmy A.; University of Alabama Tuscaloosa
Fossil galaxy systems have been described as some of the oldest systems in the universe, where the central galaxy has cannibalized most nearby member galaxies over cosmic time. While the progenitors to fossil systems have been predicted to exist in numerical simulations, little effort has gone into locating them until now. The discovery of fossil progenitors in the CASSOWARY catalog of strong gravitational lensing demonstrates that not all fossils are old, and their formation histories are more complex than originally thought. These progenitors have optical characteristics consistent with them being the transition phase between non-fossils and fossils, as we are observing the central galaxies in mid-assembly. We also identify a bias where systems acting as strong gravitational lenses are ~5 times more likely to be seen as fossils than non-lensing systems. Chandra X-ray images of eight CASSOWARY fossil progenitors show them being significantly over-luminous and hotter than comparable non-fossils which could be due to the strong lensing bias in our data, or fossils have characteristically deeper potential wells than non-fossils. Two progenitors were luminous enough to see a rise in gas temperature toward their cores which suggests these may be undergoing group mergers akin to the previously studied progenitor CSWA 2 verifying this as a viable fossil formation mechanism. Refinements to our original CASSOWARY data using the Hubble Space Telescope allowed us to disentangle complex merging environments at the centers of these eight progenitors, which further solidified the notion that progenitors are indeed transitioning toward fossil systems.
FIRST NuSTAR OBSERVATIONS OF MRK 501 WITHIN A RADIO TO TeV MULTI-INSTRUMENT CAMPAIGN
(IOP Publishing Ltd, 2015-10-08) Santander, Marcos; University of Alabama Tuscaloosa
We report on simultaneous broadband observations of the TeV-emitting blazar Markarian 501 between 2013 April 1 and August 10, including the first detailed characterization of the synchrotron peak with Swift and NuSTAR. During the campaign, the nearby BL Lac object was observed in both a quiescent and an elevated state. The broadband campaign includes observations with NuSTAR, MAGIC, VERITAS, the Fermi Large Area Telescope, Swift X-ray Telescope and UV Optical Telescope, various ground-based optical instruments, including the GASP-WEBT program, as well as radio observations by OVRO, Metsähovi, and the F-Gamma consortium. Some of the MAGIC observations were affected by a sand layer from the Saharan desert, and had to be corrected using event-by-event corrections derived with a Light Detection and Ranging (LIDAR) facility. This is the first time that LIDAR information is used to produce a physics result with Cherenkov Telescope data taken during adverse atmospheric conditions, and hence sets a precedent for the current and future ground-based gamma-ray instruments. The NuSTAR instrument provides unprecedented sensitivity in hard X-rays, showing the source to display a spectral energy distribution (SED) between 3 and 79 keV consistent with a log-parabolic spectrum and hard X-ray variability on hour timescales. None (of the four extended NuSTAR observations) show evidence of the onset of inverse-Compton emission at hard X-ray energies. We apply a single-zone equilibrium synchrotron self-Compton (SSC) model to five simultaneous broadband SEDs. We find that the SSC model can reproduce the observed broadband states through a decrease in the magnetic field strength coinciding with an increase in the luminosity and hardness of the relativistic leptons responsible for the high-energy emission.
First Observation of PeV-Energy Neutrinos with IceCube
(American Physical Society, 2013-07-08) Santander, Marcos; University of Alabama Tuscaloosa
We report on the observation of two neutrino-induced events which have an estimated deposited energy in the IceCube detector of 1.04±0.16 and 1.14±0.17 PeV, respectively, the highest neutrino energies observed so far. These events are consistent with fully contained particle showers induced by neutral-current νe,μ,τ (ν̅e,μ,τ) or charged-current νe (ν̅e) interactions within the IceCube detector. The events were discovered in a search for ultrahigh energy neutrinos using data corresponding to 615.9 days effective live time. The expected number of atmospheric background is 0.082±0.004(stat)+0.041−0.057(syst). The probability of observing two or more candidate events under the atmospheric background-only hypothesis is 2.9×10⁻³ (2.8σ) taking into account the uncertainty on the expected number of background events. These two events could be a first indication of an astrophysical neutrino flux; the moderate significance, however, does not permit a definitive conclusion at this time.
First search for atmospheric and extraterrestrial neutrino-induced cascades with the IceCube detector
(American Physical Society, 2011-10-03) Santander, Marcos; University of Alabama Tuscaloosa
We report on the first search for atmospheric and for diffuse astrophysical neutrino-induced showers (cascades) in the IceCube detector using 257 days of data collected in the year 2007–2008 with 22 strings active. A total of 14 events with energies above 16 TeV remained after event selections in the diffuse analysis, with an expected total background contribution of 8.3 ± 3.6. At 90% confidence we set an upper limit of E(^2)Φ_(90%CL) < 10^-7 GeV · cm^-2 · s^-1 · sr^-1 on the diffuse flux of neutrinos of all flavors in the energy range between 24 TeV and 6.6 PeV assuming that Φ ∝ E^-2 and the flavor composition of the ν_e : v_μ v_ τ flux is 1 : 1 :1 at the Earth. The atmospheric neutrino analysis was optimized for lower energies. A total of 12 events were observed with energies above 5 TeV. The observed number of events is consistent with the expected background, within the uncertainties.
IceCube search for dark matter annihilation in nearby galaxies and galaxy clusters
(American Physical Society, 2013-12-06) Santander, Marcos; University of Alabama Tuscaloosa
We present the results of a first search for self-annihilating dark matter in nearby galaxies and galaxy clusters using a sample of high-energy neutrinos acquired in 339.8 days of live time during 2009/10 with the IceCube neutrino observatory in its 59-string configuration. The targets of interest include the Virgo and Coma galaxy clusters, the Andromeda galaxy, and several dwarf galaxies. We obtain upper limits on the cross section as a function of the weakly interacting massive particle mass between 300 GeV and 100 TeV for the annihilation into b^¯b , W^+W^- , _Ƭ^+_Ƭ^- , µ^+ µ_- , and v^¯v. A limit derived for the Virgo cluster, when assuming a large effect from subhalos, challenges the weakly interacting massive particle interpretation of a recently observed GeV positron excess in cosmic rays.
IceCube sensitivity for low-energy neutrinos from nearby supernovae
(EDP Sciences, 2011-11-21) Santander, Marcos; University of Alabama Tuscaloosa
This paper describes the response of the IceCube neutrino telescope located at the geographic south pole to outbursts of MeV neutrinos from the core collapse of nearby massive stars. IceCube was completed in December 2010 forming a lattice of 5160 photomultiplier tubes that monitor a volume of ~1 km³ in the deep Antarctic ice for particle induced photons. The telescope was designed to detect neutrinos with energies greater than 100 GeV. Owing to subfreezing ice temperatures, the photomultiplier dark noise rates are particularly low. Hence IceCube can also detect large numbers of MeV neutrinos by observing a collective rise in all photomultiplier rates on top of the dark noise. With 2 ms timing resolution, IceCube can detect subtle features in the temporal development of the supernova neutrino burst. For a supernova at the galactic center, its sensitivity matches that of a background-free megaton-scale supernova search experiment. The sensitivity decreases to 20 standard deviations at the galactic edge (30 kpc) and 6 standard deviations at the Large Magellanic Cloud (50 kpc). IceCube is sending triggers from potential supernovae to the Supernova Early Warning System. The sensitivity to neutrino properties such as the neutrino hierarchy is discussed, as well as the possibility to detect the neutronization burst, a short outbreak of ν_e's released by electron capture on protons soon after collapse. Tantalizing signatures, such as the formation of a quark star or a black hole as well as the characteristics of shock waves, are investigated to illustrate IceCube’s capability forsupernova detection.
Lateral distribution of muons in IceCube cosmic ray events
(American Physical Society, 2013-01-07) Santander, Marcos; University of Alabama Tuscaloosa
In cosmic ray air showers, the muon lateral separation from the center of the shower is a measure of the transverse momentum that the muon parent acquired in the cosmic ray interaction. IceCube has observed cosmic ray interactions that produce muons laterally separated by up to 400 m from the shower core, a factor of 6 larger distance than previous measurements. These muons originate in high p_T (> 2 GeV/c) interactions from the incident cosmic ray, or high-energy secondary interactions. The separation distribution shows a transition to a power law at large values, indicating the presence of a hard p_T component that can be described by perturbative quantum chromodynamics. However, the rates and the zenith angle distributions of these events are not well reproduced with the cosmic ray models tested here, even those that include charm interactions. This discrepancy may be explained by a larger fraction of kaons and charmed particles than is currently incorporated in the simulations.
Limit on the diffuse flux of ultrahigh energy tau neutrinos with the surface detector of the Pierre Auger Observatory
(American Physical Society, 2009-05-01) Santander, Marcos; University of Alabama Tuscaloosa
Data collected at the Pierre Auger Observatory are used to establish an upper limit on the diffuse flux of tau neutrinos in the cosmic radiation. Earth-skimming ντ may interact in the Earth’s crust and produce a τ lepton by means of charged-current interactions. The τ lepton may emerge from the Earth and decay in the atmosphere to produce a nearly horizontal shower with a typical signature, a persistent electromagnetic component even at very large atmospheric depths. The search procedure to select events induced by τ decays against the background of normal showers induced by cosmic rays is described. The method used to compute the exposure for a detector continuously growing with time is detailed. Systematic uncertainties in the exposure from the detector, the analysis, and the involved physics are discussed. No τ neutrino candidates have been found. For neutrinos in the energy range 2×10¹⁷ eV
Measurement of Atmospheric Neutrino Oscillations with IceCube
(American Physical Society, 2013-08-19) Santander, Marcos; University of Alabama Tuscaloosa
We present the first statistically significant detection of neutrino oscillations in the high-energy regime (> 20 GeV) from an analysis of IceCube Neutrino Observatory data collected in 2010 and 2011. This measurement is made possible by the low-energy threshold of the DeepCore detector (~ 20 GeV) and benefits from the use of the IceCube detector as a veto against cosmic-ray-induced muon background. The oscillation signal was detected within a low-energy muon neutrino sample (20–100 GeV) extracted from data collected by DeepCore. A high-energy muon neutrino sample (100 GeV–10 TeV) was extracted from IceCube data to constrain systematic uncertainties. The disappearance of low-energy upward-going muon neutrinos was observed, and the nonoscillation hypothesis is rejected with more than 5σ significance. In a two-neutrino flavor formalism, our data are best described by the atmospheric neutrino oscillation parameters |Δm^2/_22| = (2.3^+0.6/_-0.5) x 10^-3 eV^2 and sin^2(2Ө_23) > 0.93, and maximum mixing is favored.
MEASUREMENT OF THE ANISOTROPY OF COSMIC-RAY ARRIVAL DIRECTIONS WITH ICECUBE
(IOP Publishing, 2010-07-16) Santander, Marcos; University of Alabama Tuscaloosa
We report the first observation of an anisotropy in the arrival direction of cosmic rays with energies in the multi-TeV region in the Southern sky using data from the IceCube detector. Between 2007 June and 2008 March, the partially deployed IceCube detector was operated in a configuration with 1320 digital optical sensors distributed over 22 strings at depths between 1450 and 2450 m inside the Antarctic ice. IceCube is a neutrino detector, but the data are dominated by a large background of cosmic-ray muons. Therefore, the background data are suitable for high-statistics studies of cosmic rays in the southern sky. The data include 4.3 billion muons produced by downward-going cosmic-ray interactions in the atmosphere; these events were reconstructed with a median angular resolution of 3° and a median energy of ~20 TeV. Their arrival direction distribution exhibits an anisotropy in right ascension with a first-harmonic amplitude of (6.4 ± 0.2 stat. ± 0.8 syst.) × 10⁻⁴.
Measurement of the Atmospheric nu(e) Flux in IceCube
(American Physical Society, 2013-04-10) Santander, Marcos; University of Alabama Tuscaloosa
We report the first measurement of the atmospheric electron neutrino flux in the energy range between approximately 80 GeV and 6 TeV, using data recorded during the first year of operation of IceCube’s DeepCore low-energy extension. Techniques to identify neutrinos interacting within the DeepCore volume and veto muons originating outside the detector are demonstrated. A sample of 1029 events is observed in 281 days of data, of which 496±66(stat)±88(syst) are estimated to be cascade events, including both electron neutrino and neutral current events. The rest of the sample includes residual backgrounds due to atmospheric muons and charged current interactions of atmospheric muon neutrinos. The flux of the atmospheric electron neutrinos is consistent with models of atmospheric neutrinos in this energy range. This constitutes the first observation of electron neutrinos and neutral current interactions in a very large volume neutrino telescope optimized for the TeV energy range.
Measurement of the cosmic ray energy spectrum with IceTop-73
(American Physical Society, 2013-08-28) Santander, Marcos; University of Alabama Tuscaloosa
We report on the measurement of the all-particle cosmic ray energy spectrum with the IceTop air shower array in the energy range from 1.58 PeV to 1.26 EeV. The IceTop air shower array is the surface component of the IceCube Neutrino Observatory at the geographical South Pole. The analysis was performed using only information from IceTop. The data used in this work were taken from June 1, 2010 to May 13, 2011. During that period the IceTop array consisted of 73 stations, compared to 81 in its final configuration. The measured spectrum exhibits a clear deviation from a single power law above the knee around 4 PeV and below 1 EeV. We observe spectral hardening around 18 PeV and steepening around 130 PeV.
Measurement of the energy spectrum of cosmic rays above 10(18) eV using the Pierre Auger Observatory
(Elsevier, 2010-03-08) Santander, Marcos; University of Alabama Tuscaloosa
We report a measurement of the flux of cosmic rays with unprecedented precision and statistics using the Pierre Auger Observatory. Based on fluorescence observations in coincidence with at least one surface detector we derive a spectrum for energies above 10¹⁸ eV. We also update the previously published energy spectrum obtained with the surface detector array. The two spectra are combined addressing the systematic uncertainties and, in particular, the influence of the energy resolution on the spectral shape. The spectrum can be described by a broken power law E^(-γ) with index γ = 3.3 below the ankle which is measured at log₁₀(E_(ankle)/eV) = 18.6. Above the ankle the spectrum is described by a power law with index 2.6 followed by a flux suppression, above about log₁₀(E/eV) = 19.5, detected with high statistical significance.
Measurements using the inelasticity distribution of multi-TeV neutrino interactions in IceCube
(American Physical Society, 2019-02-13) Santander, Marcos; University of Alabama Tuscaloosa
Inelasticity, the fraction of a neutrino’s energy transferred to hadrons, is a quantity of interest in the study of astrophysical and atmospheric neutrino interactions at multi-TeV energies with IceCube. In this work, a sample of contained neutrino interactions in IceCube is obtained from five years of data and classified as 2650 tracks and 965 cascades. Tracks arise predominantly from charged-current v_μ interactions, and we demonstrate that we can reconstruct their energy and inelasticity. The inelasticity distribution is found to be consistent with the calculation of Cooper-Sarkar et al. across the energy range from ∼ 1 to ∼ 100 TeV. Along with cascades from neutrinos of all flavors, we also perform a fit over the energy, zenith angle, and inelasticity distribution to characterize the flux of astrophysical and atmospheric neutrinos. The energy spectrum of diffuse astrophysical neutrinos is described well by a power law in both track and cascade samples, and a best-fit index γ = 2.62 ± 0.07 is found in the energy range from 3.5 TeV to 2.6 PeV. Limits are set on the astrophysical flavor composition and are compatible with a ratio of (1/3 : 1/3 : 1/3)_⊕. Exploiting the distinct inelasticity distribution of v_μ and v̅_μ interactions, the atmospheric v_μ to v̅_μ flux ratio in the energy range from 770 GeV to 21 TeV is found to be 0.77^+0.44_-0.25 times the calculation by Honda et al. Lastly, the inelasticity distribution is also sensitive to neutrino charged-current charm production. The data are consistent with a leading-order calculation, with zero charm production excluded at 91% confidence level. Future analyses of inelasticity distributions may probe new physics that affects neutrino interactions both in and beyond the Standard Model.

Browsing by Author "Santander, Marcos"

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