Exploring the association of Fermi sources with Young Stellar Objects

Massive protostars have associated bipolar outflows which can produce strong shocks when interact with the surrounding medium. In these conditions particle acceleration at relativistic velocities can occur leading to gamma ray emission, as some theoretical models predict. To identify young stellar objects (YSO) that may emit gamma rays we have crossed the Fermi First Year Catalog with some catalogs of known YSOs, and we have conducted Montecarlo simulations to find the probability of chance coincidence. With this crossing we obtained a list of YSOs spatially coincident with Fermi sources that may show gamma ray emission. Our results indicate that about 70% of the candidates should be gamma-ray sources with a confidence of 5 sigma. We have studied the coincidences one by one to check the viability of these YSOs as potential counterparts of Fermi sources and plan further detailed observations of few of them.Fil: Munar Adrover. Pere. Universitat de Barcelona; EspañaFil: Paredes, Josep Maria. Universitat de Barcelona; EspañaFil: Romero, Gustavo Esteban. Provincia de Buenos Aires. Gobernación. Comisión de Investigaciones Científicas. Instituto Argentino de Radioastronomía. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - La Plata. Instituto Argentino de Radioastronomía; ArgentinaIX Scientific Meeting of the Spanish Astronomical Society. Highlights of Spanish Astrophysics VIMadridEspañaSpanish Astronomical Societ

The Blazar PG 1553+113 as a Binary System of Supermassive Black Holes

The BL Lac PG 1553+113 has been continuously monitored in gamma rays with Fermi-LAT for over 9 years. Its updated light curve now includes 5 iterations of a main pattern comprising a high peak and a longer trough, with a period P \sim 2.2 yr. Our analysis of 2015-2017 data confirms the occurrence in January 2017 of a new peak fitting in the previous trend. In addition, we identify secondary peaks ("twin peaks") that occur in closely symmetric pairs on both sides of most main peaks, including the last one; their occurrence is supported by correlated X-ray outbursts. We stress that the above features strongly point to binary dynamics in a system of two black holes (BHs) of some 10^8 and 10^7 M_sun. At periastron the smaller BH periodically stresses the jet j_1 launched by the heavier companion, and triggers MHD-kinetic tearing instabilities. These lead to magnetic reconnections and to acceleration of electrons that produce synchrotron emission from the optical to X-ray bands, and inverse Compton scattering into the GeV range. For the origin of the twin peaks we discuss two possibilities: a single-jet model, based on added instabilities induced in j_1 by the smaller companion BH on its inner orbital arc; and a two-jet model with the smaller BH supporting its own, precessing jet j_2 that contributes lower, specific GeV emissions. Such behaviors combining time stability with amplitude variations betray plasma instabilities driven in either jet by binary dynamics, and can provide a double signature of the long-sought supermassive BH binaries.Comment: 15 pages, 5 figures, accepeted by ApJ on December 21, 201

A study of the association of Fermi sources with massive young galactic objects

Massive protostars have associated bipolar outflows that can produce strong shocks when they interact with the surrounding medium. At these shocks particles can be accelerated up to relativistic energies. Relativistic electrons and protons can then produce gamma-ray emission, as some theoretical models predict. To identify young galactic objects that may emit gamma rays, we crossed the Fermi First Year Catalog with some catalogs of known massive young stellar objects (MYSOs), early type stars, and OB associations, and we implemented Monte Carlo simulations to find the probability of chance coincidences. We obtained a list of massive MYSOs that are spatially coincident with Fermi sources. Our results indicate that \sim 70% of these candidates should be gamma-ray sources with a confidence of \sim 5{\sigma}. We studied the coincidences one by one to check the viability of these young sources as potential counterparts to Fermi sources and made a short list of best targets for new detailed multifrequency observations. The results for other type of young galactic objects are not conclusive

The 2009 multiwavelength campaign on Mrk 421: Variability and correlation studies

Aims: We perform an extensive characterization of the broadband emission of Mrk 421, as well as its temporal evolution, during the non-flaring (low) state. The high brightness and nearby location (z = 0.031) of Mrk 421 make it an excellent laboratory to study blazar emission. The goal is to learn about the physical processes responsible for the typical emission of Mrk 421, which might also be extended to other blazars that are located farther away and hence are more difficult to study. Methods: We performed a 4.5-month multi-instrument campaign on Mrk 421 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. This extensive radio to very-high-energy (VHE; E> 100 GeV) γ-ray dataset provides excellent temporal and energy coverage, which allows detailed studies of the evolution of the broadband spectral energy distribution. Results: 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. Conclusions: 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 Mrk 421 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. Appendix A is available in electronic form at http://www.aanda.orgThe complete data set shown in Fig. 1 is 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/576/A12

Multiwavelength observations of Mrk 501 in 2008

Context. Blazars are variable sources on various timescales over a broad energy range spanning from radio to very high energy (>100 GeV, hereafter VHE). Mrk 501 is one of the brightest blazars at TeV energies and has been extensively studied since its first VHE detection in 1996. However, most of the γ-ray studies performed on Mrk 501 during the past years relate to flaring activity, when the source detection and characterization with the available γ-ray instrumentation was easier toperform. Aims: Our goal is to characterize the source γ-ray emission in detail, together with the radio-to-X-ray emission, during the non-flaring (low) activity, which is less often studied than the occasional flaring (high) activity. Methods: We organized a multiwavelength (MW) campaign on Mrk 501 between March and May 2008. This multi-instrument effort included the most sensitive VHE γ-ray instruments in the northern hemisphere, namely the imaging atmospheric Cherenkov telescopes MAGIC and VERITAS, as well as Swift, RXTE, the F-GAMMA, GASP-WEBT, and other collaborations and instruments. This provided extensive energy and temporal coverage of Mrk 501 throughout the entire campaign. Results: Mrk 501 was found to be in a low state of activity during the campaign, with a VHE flux in the range of 10%-20% of the Crab nebula flux. Nevertheless, significant flux variations were detected with various instruments, with a trend of increasing variability with energy and a tentative correlation between the X-ray and VHE fluxes. The broadband spectral energy distribution during the two different emission states of the campaign can be adequately described within the homogeneous one-zone synchrotron self-Compton model, with the (slightly) higher state described by an increase in the electron number density. Conclusions: The one-zone SSC model can adequately describe the broadband spectral energy distribution of the source during the two months covered by the MW campaign. This agrees with previous studies of the broadband emission of this source during flaring and non-flaring states. We report for the first time a tentative X-ray-to-VHE correlation during such a low VHE activity. Although marginally significant, this positive correlation between X-ray and VHE, which has been reported many times during flaring activity, suggests that the mechanisms that dominate the X-ray/VHE emission during non-flaring-activity are not substantially different from those that are responsible for the emission during flaring activity. The data for Figs. 2 and 5 are only available at the CDS via anonymous ftp t

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

Very High Energy γ-Rays from the Universe's Middle Age: Detection of the z = 0.940 Blazar PKS 1441+25 with MAGIC

The flat-spectrum radio quasar PKS 1441+25 at a redshift of z = 0.940 is detected between 40 and 250 GeV with a significance of 25.5σ using the MAGIC telescopes. Together with the gravitationally lensed blazar QSO B0218+357 (z = 0.944), PKS 1441+25 is the most distant very high energy (VHE) blazar detected to date. The observations were triggered by an outburst in 2015 April seen at GeV energies with the Large Area Telescope on board Fermi. Multi-wavelength observations suggest a subdivision of the high state into two distinct flux states. In the band covered by MAGIC, the variability timescale is estimated to be 6.4 ± 1.9 days. Modeling the broadband spectral energy distribution with an external Compton model, the location of the emitting region is understood as originating in the jet outside the broad-line region (BLR) during the period of high activity, while being partially within the BLR during the period of low (typical) activity. The observed VHE spectrum during the highest activity is used to probe the extragalactic background light at an unprecedented distance scale for ground-based gamma-ray astronomy

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