171 research outputs found
Biological response to geochemical and hydrological processes in a shallow submarine cave
The Croatian coastal karst abounds in submerged caves that host a variety of environmental conditions depending on the geomorphology, depth and submarine groundwater discharge. One example is the Y-Cave, a shallow, mostly submerged, horizontal cave on Dugi Otok Island, on the eastern Adriatic coast. This study was aimed at examining the temporal and spatial variability of the marine cave environment, including temperature, salinity, light intensity, cave morphology and hydrodynamism, along with the dissolutional effect caused by the mixing of sea and freshwater. The general distribution of organisms in the Y-Cave was positively correlated to the light gradient and reduced water circulation, thus the highest species diversity and abundance were recorded in the front part of the cave. The phylum Porifera was the most dominant group, and the poriferan species diversity in the cave ranks among the ten highest in the Mediterranean. The middle part of the cave, although completely dark, hosts an abundant population of the gastropod Homalopoma sanguineum and clusters of the gregarious brachiopod Novocrania anomala, whose presence could be connected to tidal hydrodynamics. The absence/scarcity of sessile marine organisms and pronounced corrosion marks at shallow depths inside the cave suggest a freshwater impact in the upper layers of the water column. A year long experiment with carbonate tablets revealed three different, independent ongoing processes affected by the position in the cave: bioaccumulation, dissolution and mechanical erosion. The results of long-term temperature readings also revealed water column stratification within the cave, which was not disturbed by either tidal or wave action. The shallow, partly submerged and relatively small Y-Cave is characterised by a suite of complex environmental conditions, which, together with the resulting distribution of organisms, are unique to this cave
Detection of bridge emission above 50 GeV from the Crab pulsar with the MAGIC telescopes
The Crab pulsar is the only astronomical pulsed source detected at very high
energy (VHE, E>100GeV) gamma-rays. The emission mechanism of VHE pulsation is
not yet fully understood, although several theoretical models have been
proposed. In order to test the new models, we measured the light curve and the
spectra of the Crab pulsar with high precision by means of deep observations.
We analyzed 135 hours of selected MAGIC data taken between 2009 and 2013 in
stereoscopic mode. In order to discuss the spectral shape in connection with
lower energies, 4.6 years of {\it Fermi}-LAT data were also analyzed. The known
two pulses per period were detected with a significance of and
. In addition, significant emission was found between the two
pulses with . We discovered the bridge emission above 50 GeV
between the two main pulses. This emission can not be explained with the
existing theories. These data can be used for testing new theoretical models.Comment: 5 pages, 4 figure
First broadband characterization and redshift determination of the VHE blazar MAGIC J2001+439
We aim to characterize the broadband emission from 2FGL J2001.1+4352, which
has been associated with the unknown-redshift blazar MG4 J200112+4352. Based on
its gamma-ray spectral properties, it was identified as a potential very high
energy (VHE; E > 100 GeV) gamma-ray emitter. The source was observed with MAGIC
first in 2009 and later in 2010 within a multi-instrument observation campaign.
The MAGIC observations yielded 14.8 hours of good quality stereoscopic data.
The object was monitored at radio, optical and gamma-ray energies during the
years 2010 and 2011. The source, named MAGIC J2001+439, is detected for the
first time at VHE with MAGIC at a statistical significance of 6.3 {\sigma} (E >
70 GeV) during a 1.3-hour long observation on 2010 July 16. The
multi-instrument observations show variability in all energy bands with the
highest amplitude of variability in the X-ray and VHE bands. We also organized
deep imaging optical observations with the Nordic Optical Telescope in 2013 to
determine the source redshift. We determine for the first time the redshift of
this BL Lac object through the measurement of its host galaxy during low blazar
activity. Using the observational evidence that the luminosities of BL Lac host
galaxies are confined to a relatively narrow range, we obtain z = 0.18 +/-
0.04. Additionally, we use the Fermi-LAT and MAGIC gamma-ray spectra to provide
an independent redshift estimation, z = 0.17 +/- 0.10. Using the former (more
accurate) redshift value, we adequately describe the broadband emission with a
one-zone SSC model for different activity states and interpret the few-day
timescale variability as produced by changes in the high-energy component of
the electron energy distribution.Comment: 17 pages, 15 figures, Accepted for publication in A&
The 2009 multiwavelength campaign on Mrk 421: Variability and correlation studies
We performed a 4.5-month multi-instrument campaign (from radio to VHE gamma
rays) on Mrk421 between January 2009 and June 2009, which included VLBA,
F-GAMMA, GASP-WEBT, Swift, RXTE, Fermi-LAT, MAGIC, and Whipple, among other
instruments and collaborations. Mrk421 was found in its typical (non-flaring)
activity state, with a VHE flux of about half that of the Crab Nebula, yet the
light curves show significant variability at all wavelengths, the highest
variability being in the X-rays. We determined the power spectral densities
(PSD) at most wavelengths and found that all PSDs can be described by
power-laws without a break, and with indices consistent with pink/red-noise
behavior. We observed a harder-when-brighter behavior in the X-ray spectra and
measured a positive correlation between VHE and X-ray fluxes with zero time
lag. Such characteristics have been reported many times during flaring
activity, but here they are reported for the first time in the non-flaring
state. We also observed an overall anti-correlation between optical/UV and
X-rays extending over the duration of the campaign.
The harder-when-brighter behavior in the X-ray spectra and the measured
positive X-ray/VHE correlation during the 2009 multi-wavelength campaign
suggests that the physical processes dominating the emission during non-flaring
states have similarities with those occurring during flaring activity. In
particular, this observation supports leptonic scenarios as being responsible
for the emission of Mrk421 during non-flaring activity. Such a temporally
extended X-ray/VHE correlation is not driven by any single flaring event, and
hence is difficult to explain within the standard hadronic scenarios. The
highest variability is observed in the X-ray band, which, within the one-zone
synchrotron self-Compton scenario, indicates that the electron energy
distribution is most variable at the highest energies.Comment: Accepted for publication in A&A, 18 pages, 14 figures (v2 has a small
modification in the acknowledgments, and also corrects a typo in the field
"author" in the metadata
MAGIC observations and multiwavelength properties of the quasar 3C279 in 2007 and 2009
3C 279, the first quasar discovered to emit VHE gamma-rays by the MAGIC telescope in 2006, was reobserved by MAGIC in January 2007 during a major optical flare and from December 2008 to April 2009 following an alert from the Fermi space telescope on an exceptionally high gamma -ray state. The January 2007 observations resulted in a detection on January 16 with significance 5.2 sigma, corresponding to a F(> 150 GeV) (3.8 \pm 0.8) \cdot 10^-11 ph cm^-2 s^-1 while the overall data sample does not show significant signal. The December 2008 - April 2009 observations did not detect the source. We study the multiwavelength behavior of the source at the epochs of MAGIC observations, collecting quasi-simultaneous data at optical and X-ray frequencies and for 2009 also gamma-ray data from Fermi. We study the light curves and spectral energy distribution of the source. The spectral energy distributions of three observing epochs (including the February 2006, which has been previously published in Albert et al. 2008a) are modeled with one-zone inverse Compton models and the emission on January 16, 2007 also with two zone model and with a lepto-hadronic model. We find that the VHE gamma-ray emission detected in 2006 and 2007 challenges standard one-zone model, based on relativistic electrons in a jet scattering broad line region photons, while the other studied models fit the observed spectral energy distribution more satisfactorily
Statistics of VHE \u3b3-rays in temporal association with radio giant pulses from the Crab pulsar
Aims. The aim of this study is to search for evidence of a common emission engine between radio giant pulses (GPs) and very-high-energy (VHE, E& x2004;> & x2004;100 GeV) gamma-rays from the Crab pulsar. Methods. We performed 16 h of simultaneous observations of the Crab pulsar at 1.4 GHz with the Effelsberg radio telescope and the Westerbork Synthesis Radio Telescope (WSRT), and at energies above 60 GeV we used the Major Atmospheric Gamma-ray Imaging Cherenkov (MAGIC) telescopes. We searched for a statistical correlation between the radio and VHE gamma-ray emission with search windows of different lengths and different time lags to the arrival times of a radio GP. A dedicated search for an enhancement in the number of VHE gamma-rays correlated with the occurrence of radio GPs was carried out separately for the P1 and P2 phase ranges, respectively. Results. In the radio data sample, 99444 radio GPs were detected. We find no significant correlation between the GPs and VHE photons in any of the search windows. Depending on phase cuts and the chosen search windows, we find upper limits at a 95% confidence level on an increase in VHE gamma-ray events correlated with radio GPs between 7% and 61% of the average Crab pulsar VHE flux for the P1 and P2 phase ranges, respectively. This puts upper limits on the flux increase during a radio GP between 12% and 2900% of the pulsed VHE flux, depending on the search window duration and phase cuts. This is the most stringent upper limit on a correlation between gamma-ray emission and radio GPs reported so far
A search for Very High Energy gamma-ray emission from Scorpius X-1 with the MAGIC telescopes
The acceleration of particles up to GeV or higher energies in microquasars
has been the subject of considerable theoretical and observational efforts in
the past few years. Sco X-1 is a microquasar from which evidence of highly
energetic particles in the jet has been found when it is in the so-called
Horizontal Branch (HB), a state when the radio and hard X-ray fluxes are higher
and a powerful relativistic jet is present. Here we present the first very high
energy gamma-ray observations of Sco X-1 obtained with the MAGIC telescopes. An
analysis of the whole dataset does not yield a significant signal, with 95% CL
flux upper limits above 300 GeV at the level of 2.4x10^{-12} ph/cm^2/s.
Simultaneous RXTE observations were conducted to search for TeV emission during
particular X-ray states of the source. A selection of the gamma-ray data
obtained during the HB based on the X-ray colors did not yield a signal either,
with an upper limit of 3.4x10^{-12} ph/cm^2/s. These upper limits place a
constraint on the maximum TeV luminosity to non-thermal X-ray luminosity of
L_{VHE}/L_{ntX}<0.02, that can be related to a maximum TeV luminosity to jet
power ratio of L_{VHE}/L_{j}<10^{-3}. Our upper limits indicate that the
underlying high-energy emission physics in Sco X-1 must be inherently different
from that of the hitherto detected gamma-ray binaries.Comment: 5 pages, 2 figures, 2 tables. Version as published in ApJ
Discovery of very high energy γ-ray emission from the blazar 1ES0033+595 by the MAGIC telescopes
The number of known very high energy (VHE) blazars is ∼50, which is very small in comparison to the number of blazars detected in other frequencies. This situation is a handicap for population studies of blazars, which emit about half of their luminosity in the γ-ray domain. Moreover, VHE blazars, if distant, allow for the study of the environment that the high-energy γ-rays traverse in their path towards the Earth, like the extragalactic background light (EBL) and the intergalactic magnetic field (IGMF), and hence they have a special interest for the astrophysics community. We present the first VHE detection of 1ES0033+595 with a statistical significance of 5.5σ. The VHE emission of this object is constant throughout the MAGIC observations (2009 August and October), and can be parametrized with a power law with an integral flux above 150GeV of (7.1 ± 1.3) × 10−12 photons cm−2 s−1 and a photon index of (3.8±0.7). We model its spectral energy distribution (SED) as the result of inverse Compton scattering of synchrotron photons. For the study of the SED, we used simultaneous optical R-band data from the KVA telescope, archival X-ray data by Swift as well as INTEGRAL, and simultaneous high-energy (HE, 300MeV-10GeV) γ-ray data from the Fermi Large Area Telescope (LAT) observatory. Using the empirical approach of Prandini etal. (2010) and the Fermi LAT and MAGIC spectra for this object, we estimate the redshift of this source to be 0.34±0.08±0.05. This is a relevant result because this source is possibly one of the 10 most distant VHE blazars known to date, and with further (simultaneous) observations could play an important role in blazar population studies, as well as future constraints on the EBL andIGM
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