Results for Greenland halibut, American plaice and Atlantic cod of the Spanish survey in NAFO Div. 3NO for the period 1997-2018

Greenland halibut (Reinhardtius hippoglossoides), American plaice (Hippoglossoides platessoides) and Atlantic cod (Gadus morhua) indices from the bottom trawl survey that Spain carries out in Spring since 1995 in Div. 3NO of the NAFO Regulatory Area are presented. Biomass, stratified mean catches and mean number per tow for the three species are presented since 1997, year in which the survey extended the depth strata. Mean catch per tow, length distribution and age distribution are presented for the last five years (2014-2018). Greenland halibut biomass and abundance estimates presented a decreasing trend since 1999, cut in 2007-2009 with a high increase. In 2011 the biomass drops under the 2008 value, being stable since then until 2014 with a slight increase in 2015-2018 comprising a big increase in 2017, reaching the maximum of the series. In last years it can be seen a presence of juveniles, mainly in 2004, but the greatest lengths have failed, although in 2009 there is a quite good presence of individuals of ages 6-7 and in 2010 between 5-7. In 2011-2018 the presence of all ages is poor, although in 2015-2016 an increase in the range of the length can be seen with regards to last years. For American plaice we can see a stable trend from 1999 to 2015, reaching a maximum of mean catch and number in 2006, and a severe decline since 2016. The greatest recruitment in the presented series occurred in 2004 and we can follow their mode along the years. No good recruitments were seen since then. The 2016 ALK for American plaice was not sexed. The 2017 and 2018 ALKs for American plaice are not available yet, so the 2016 ALK was used. In last years the level of all the ages is low. For Atlantic cod, it can be seen a low biomass until 2008, being higher and variable since then, reaching a historical maximum in 2014. From 2015, biomass decreased reaching in 2018 poor values at the level of the 2006 biomass. In 2007-2008 the youngest length classes were much over the rest of the length classes. With the 2006 cohort the series reaches the maximum number of its historical values at five years in 2011. There have been no good recruitments since 2009, although in 2015 and 2016 a discrete presence of individuals of age 1 can be seen

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. Aims. In order to test new models, we measured the light curve and the spectra of the Crab pulsar with high precision by means of deep observations. Methods. 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, 5.5 years of Fermi-LAT data were also analyzed. Results. The known two pulses per period were detected with a significance of 8.0 σ and 12.6 σ. In addition, significant emission was found between the two pulses with 6.2 σ. Conclusions. 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

The major upgrade of the MAGIC telescopes, Part I: The hardware improvements and the commissioning of the system

The MAGIC telescopes are two Imaging Atmospheric Cherenkov Telescopes (IACTs) located on the Canary island of La Palma. The telescopes are designed to measure Cherenkov light from air showers initiated by gamma rays in the energy regime from around 50 GeV to more than 50 TeV. The two telescopes were built in 2004 and 2009, respectively, with different cameras, triggers and readout systems. In the years 2011-2012 the MAGIC collaboration undertook a major upgrade to make the stereoscopic system uniform, improving its overall performance and easing its maintenance. In particular, the camera, the receivers and the trigger of the first telescope were replaced and the readout of the two telescopes was upgraded. This paper (Part I) describes the details of the upgrade as well as the basic performance parameters of MAGIC such as raw data treatment, linearity in the electronic chain and sources of noise. In Part II, we describe the physics performance of the upgraded system

Teraelectronvolt pulsed emission from the Crab Pulsar detected by MAGIC

Aims: We investigate the extension of the very high-energy spectral tail of the Crab Pulsar at energies above 400 GeV. Methods: We analyzed ~320 h of good-quality Crab data obtained with the MAGIC telescope from February 2007 to April 2014. Results: We report the most energetic pulsed emission ever detected from the Crab Pulsar reaching up to 1.5 TeV. The pulse profile shows two narrow peaks synchronized with those measured in the GeV energy range. The spectra of the two peaks follow two different power-law functions from 70 GeV up to 1.5 TeV and connect smoothly with the spectra measured above 10 GeV by the Large Area Telescope (LAT) on board the Fermi satellite. When making a joint fit of the LAT and MAGIC data above 10 GeV the photon indices of the spectra differ by 0.5 ± 0.1. Conclusions: Using data from the MAGIC telescopes we measured the most energetic pulsed photons from a pulsar to date. Such TeV pulsed photons require a parent population of electrons with a Lorentz factor of at least 5 × 106. These results strongly suggest IC scattering off low-energy photons as the emission mechanism and a gamma-ray production region in the vicinity of the light cylinder

MAGIC observations of MWC 656, the only known Be/BH system

Context. MWC 656 has recently been established as the first observationally detected high-mass X-ray binary system containing a Be star and a black hole (BH). The system has been associated with a gamma-ray flaring event detected by the AGILE satellite in July 2010. Aims: Our aim is to evaluate whether the MWC 656 gamma-ray emission extends to very high energy (VHE > 100 GeV) gamma rays. Methods: We observed MWC 656 with the MAGIC telescopes for ~23 h during two observation periods: between May and June 2012, and in June 2013. During the last period, observations were performed contemporaneously with X-ray (XMM-Newton) and optical (STELLA) instruments. Results: We did not detect the MWC 656 binary system at TeV energies with the MAGIC telescopes in either of the two campaigns. Upper limits (ULs) to the integral flux above 300 GeV have been set, as well as differential ULs at a level of ~5% of the Crab nebula flux. The results obtained from the MAGIC observations do not support persistent emission of VHE gamma rays from this system at a level of 2.4% the Crab flux

Results for Greenland halibut, American plaice and Atlantic cod of the Spanish survey in NAFO Div. 3NO for the period 1997-2019

Greenland halibut (Reinhardtius hippoglossoides), American plaice (Hippoglossoides platessoides) and Atlantic cod (Gadus morhua) indices from the bottom trawl survey that Spain carries out in Spring since 1995 in Div. 3NO of the NAFO Regulatory Area are presented. Biomass, stratified mean catches and mean number per tow for the three species are presented since 1997, year in which the survey extended the depth strata. Mean catch per tow, length distribution and age distribution (this last except for American plaice) are presented for the last five years (2015-2019). Greenland halibut biomass and abundance estimates presented a decreasing trend since 1999, cut in 2007- 2009 with a high increase. In 2011 the biomass drops under the 2008 value, being stable since then until 2014 with a slight increase in 2015-2019 comprising a big increase in 2017, reaching the maximum of the series. In last years it can be seen a presence of juveniles, mainly in 2004, but the greatest lengths have failed, although in 2009 there is a quite good presence of individuals of ages 6-7 and in 2010 between 5-7. In 2011-2019 the presence of all ages is poor. In 2018 the mode was at 1-2 years, and 2-3 years in 2019, suggesting a fairly strong 2017 cohort. For American plaice we can see a slightly increasing trend from 1999 to 2015, reaching a maximum of mean catch and number in 2006, and a severe decline since 2016, being the 2019 the lowest value of the entire series. The greatest recruitment in the presented series occurred in 2004 and we can follow their mode along the years. No good recruitments were seen since then. In last years the level of all the ages is low. No 2019 age indices are available at this moment. For Atlantic cod, it can be seen a low biomass until 2008, being higher and variable since then, reaching a historical maximum in 2014. From 2015, biomass decreased reaching in 2019 poor values at the level of the 2005 biomass. In 2007-2008 the youngest length classes were much over the rest of the length classes. With the 2006 cohort the series reaches the maximum number of its historical values at five years in 2011. There have been no good recruitments since 2009, although in 2015 and 2016 a discrete presence of individuals of age 1 can be seen

Results of the Spanish survey in NAFO Division 3NO

Greenland halibut (Reinhardtius hippoglossoides), American plaice (Hippoglossoides platessoides), Atlantic cod (Gadus morhua), yellowtail flounder (Limanda ferruginea), redfish (Sebastes spp.), witch flounder (Glyptocephalus cynoglossus), roughhead grenadier (Macrourus berglax), thorny skate (Amblyraja radiata), white hake (Urophycis tenuis), squid (Illex illecebrosus) and capelin (Mallotus villosus) indices from the bottom trawl survey that Spain carries out in Spring since 1995 in Divisions 3NO of the NAFO Regulatory Area are presented. In 2020, the survey was not carried out due to the COVID pandemic situation. The presented indices are biomass by stratum, total length distribution and a and b parameters for the length-weight relationship; age distribution is also presented for Greenland halibut, Atlantic cod and American plaice.Versión del editor

Unprecedented study of the broadband emission of Mrk 421 during flaring activity in March 2010

Context. Because of its proximity, Mrk 421 is one of the best sources on which to study the nature of BL Lac objects. Its proximity allows us to characterize its broadband spectral energy distribution (SED). Aims: The goal is to better understand the mechanisms responsible for the broadband emission and the temporal evolution of Mrk 421. These mechanisms may also apply to more distant blazars that cannot be studied with the same level of detail. Methods: A flare occurring in March 2010 was observed for 13 consecutive days (from MJD 55 265 to MJD 55 277) with unprecedented wavelength coverage from radio to very high energy (VHE; E> 100 GeV) γ-rays with MAGIC, VERITAS, Whipple, Fermi-LAT, MAXI, RXTE, Swift, GASP-WEBT, and several optical and radio telescopes. We modeled the day-scale SEDs with one-zone and two-zone synchrotron self-Compton (SSC) models, investigated the physical parameters, and evaluated whether the observed broadband SED variability can be associated with variations in the relativistic particle population. Results: The activity of Mrk 421 initially was high and then slowly decreased during the 13-day period. The flux variability was remarkable at the X-ray and VHE bands, but it was minor or not significant at the other bands. The variability in optical polarization was also minor. These observations revealed an almost linear correlation between the X-ray flux at the 2-10 keV band and the VHE γ-ray flux above 200 GeV, consistent with the γ-rays being produced by inverse-Compton scattering in the Klein-Nishina regime in the framework of SSC models. The one-zone SSC model can describe the SED of each day for the 13 consecutive days reasonably well, which once more shows the success of this standard theoretical scenario to describe the SEDs of VHE BL Lacs such as Mrk 421. This flaring activity is also very well described by a two-zone SSC model, where one zone is responsible for the quiescent emission, while the other smaller zone, which is spatially separated from the first, contributes to the daily variable emission occurring at X-rays and VHE γ-rays. The second blob is assumed to have a smaller volume and a narrow electron energy distribution with 3 × 104<γ< 6 × 105, where γ is the Lorentz factor of the electrons. Such a two-zone scenario would naturally lead to the correlated variability at the X-ray and VHE bands without variability at the optical/UV band, as well as to shorter timescales for the variability at the X-ray and VHE bands with respect to the variability at the other bands. Conclusions: Both the one-zone and the two-zone SSC models can describe the daily SEDs via the variation of only four or five model parameters, under the hypothesis that the variability is associated mostly with the underlying particle population. This shows that the particle acceleration and cooling mechanism that produces the radiating particles might be the main mechanism responsible for the broadband SED variations during the flaring episodes in blazars. The two-zone SSC model provides a better agreement with the observed SED at the narrow peaks of the low- and high-energy bumps during the highest activity, although the reported one-zone SSC model could be further improved by varying the parameters related to the emitting region itself (δ, B and R), in addition to the parameters related to the particle population. Appendices are available in electronic form at http://www.aanda.orgMulti-wavelength light curves (data in Fig. 1) and broadband spectral energy distributions (the data in Figs. 7, 8a-9f, 12a-13f) are only available at the CDS via anonymous ftp to http://cdsarc.u-strasbg.fr (ftp://130.79.128.5) or via http://cdsarc.u-strasbg.fr/viz-bin/qcat?J/A+A/578/A2