Observations of Very High Energy Gamma-Rays during Moonlight and Twilight with the MAGIC Telescope

We study the capability of the MAGIC telescope to observe under moderate moonlight. TeV gamma-ray signals from the Crab nebula were detected with the MAGIC telescope during periods when the Moon was above the horizon and during twilight. This was accomplished by increasing the trigger discriminator thresholds. No change is necessary in the high voltage settings since the camera PMTs were especially designed to avoid high currents. We characterize the telescope performance by studying the effect of the moonlight on the gamma-ray detection efficiency and sensitivity, as well as on the energy threshold.Comment: Contribution to the 30th ICRC, Merida Mexico, July 2007 on behalf of the MAGIC Collaboratio

TeV Astronomy

With the successful realization of the current-generation of ground-based detectors, TeV Astronomy has entered into a new era. We review recent advances in VHE astronomy, focusing on the potential of Imaging Atmospheric Cherenkov Telescopes (IACTs), and highlight astrophysical implications of the results obtained within recent years

Very high energy gamma-ray follow-up observations of novae and dwarf novae with the MAGIC telescopes

In the last few years the Fermi-LAT instrument has detected GeV gamma-ray emission from several novae. Such GeV emission can be interpreted in terms of inverse Compton emission from electrons accelerated in the shock or in terms of emission from hadrons accelerated in the same conditions. The latter might reach much higher energies and could produce a second component in the gamma-ray spectrum at TeV energies. We perform follow-up observations of selected novae and dwarf novae in search of the second component in TeV energy gamma rays. This can shed light on the acceleration process of leptons and hadrons in nova explosions. We have performed observations with the MAGIC telescopes of 3 sources, a symbiotic nova YY Her, a dwarf nova ASASSN-13ax and a classical nova V339 Del, shortly after their outbursts. We did not detect TeV gamma-ray emission from any of the objects observed. The TeV upper limits from MAGIC observations and the GeV detection by Fermi constrain the acceleration parameters for electrons and hadrons.Comment: Proceedings of the 34th International Cosmic Ray Conference, 30 July- 6 August, 2015, The Hague, The Netherlands. The content of this submission is similar to our paper in the Fermi Symposium of novae observations with MAGIC, which appeared as arXiv:1502.05853. arXiv admin note: substantial text overlap with arXiv:1502.0585

Observations of one young and three middle-aged γ\gamma-ray pulsars with the Gran Telescopio Canarias

We used the 10.4m Gran Telescopio Canarias to search for the optical counterparts to four isolated $\gamma$-ray pulsars, all detected in the X-rays by either \xmm\ or \chan\ but not yet in the optical. Three of them are middle-aged pulsars -- PSR\, J1846+0919 (0.36 Myr), PSR\, J2055+2539 (1.2 Myr), PSR\, J2043+2740 (1.2 Myr) -- and one, PSR\, J1907+0602, is a young pulsar (19.5 kyr). For both PSR\, J1907+0602 and PSR\, J2055+2539 we found one object close to the pulsar position. However, in both cases such an object cannot be a viable candidate counterpart to the pulsar. For PSR\, J1907+0602, because it would imply an anomalously red spectrum for the pulsar and for PSR\, J2055+2539 because the pulsar would be unrealistically bright ($r'=20.34\pm0.04$) for the assumed distance and interstellar extinction. For PSR\, J1846+0919, we found no object sufficiently close to the expected position to claim a possible association, whereas for PSR\, J2043+2740 we confirm our previous findings that the object nearest to the pulsar position is an unrelated field star. We used our brightness limits ($g' \approx 27$), the first obtained with a large-aperture telescope for both PSR\, J1846+0919 and PSR\, J2055+2539, to constrain the optical emission properties of these pulsars and investigate the presence of spectral turnovers at low energies in their multi-wavelength spectra.Comment: 10 pages, 11 figures, accpted for publication in MNRA

Discovery of VHE gamma-rays from the vicinity of the shell-type SNR G318.2+0.1 with H.E.S.S

The on-going H.E.S.S. Galactic Plane Survey continues to reveal new sources of VHE gamma-rays. In particular, recent re-observations of the region around the shell-type supernova remnant (SNR) G318.2+0.1 have resulted in the discovery of statistically-significant very-high-energy (VHE) gamma-ray emission from an extended region. Although the source remains unidentified, archival observations of CO12 in the region provide an opportunity to investigate a potential SNR/molecular cloud interaction. The morphological properties of this newly-discovered VHE gamma-ray source HESSJ1457-593 are presented and discussed in light of the multi-wavelength data available.Comment: 7 pages, 2 figures. Proc. of the 25th TEXAS Symposium on Relativistic Astrophysics. To appear in Proceedings of Scienc

Observations of three young gamma-ray pulsars with the Gran Telescopio Canarias

We report the analysis of the first deep optical observations of three isolated $\gamma$-ray pulsars detected by the {\em Fermi Gamma-ray Space Telescope}: the radio-loud PSR\, J0248+6021 and PSR\, J0631+1036, and the radio-quiet PSR\, J0633+0632. The latter has also been detected in the X rays. The pulsars are very similar in their spin-down age ($\tau \sim$40--60 kyrs), spin-down energy ($\dot{E} \sim10^{35}$ erg s$^{-1}$), and dipolar surface magnetic field ($B \sim 3$--$5\times10^{12}$ G). These pulsars are promising targets for multi-wavelength observations, since they have been already detected in $\gamma$ rays and in radio or X-rays. None of them has been detected yet in the optical band. We observed the three pulsar fields in 2014 with the Spanish 10.4m Gran Telescopio Canarias (GTC). We could not find any candidate optical counterpart to the three pulsars close to their most recent radio or {\em Chandra} positions down to $3 \sigma$ limits of $g'\sim27.3$, $g'\sim27$, $g'\sim27.3$ for PSR\, J0248+6021, J0631+1036, and J0633+0632, respectively. From the inferred optical upper limits and estimated distance and interstellar extinction, we derived limits on the pulsar optical luminosity. We also searched for the X-ray counterpart to PSR\, J0248+6021 with \chan\ but we did not detect the pulsar down to a 3$\sigma$ flux limit of $5 \times 10^{-14}$ erg cm$^{-2}$ s$^{-1}$ (0.3--10 keV). For all these pulsars, we compared the optical flux upper limits with the extrapolations in the optical domain of the $\gamma$-ray spectra and compared their multi-wavelength properties with those of other $\gamma$-ray pulsars of comparable age.Comment: 12 pages, 5 figures, accepted for publication in MNRA

SAX J1808.4-3658, an accreting millisecond pulsar shining in gamma rays?

We report the detection of a possible gamma-ray counterpart of the accreting millisecond pulsar SAX J1808.4-3658. The analysis of ~6 years of data from the Large Area Telescope on board the Fermi Gamma-ray Space Telescope (Fermi-LAT) within a region of 15deg radius around the position of the pulsar reveals a point gamma-ray source detected at a significance of ~6 sigma (Test Statistic TS = 32), with position compatible with that of SAX J1808.4-3658 within 95% Confidence Level. The energy flux in the energy range between 0.6 GeV and 10 GeV amounts to (2.1 +- 0.5) x 10-12 erg cm-2 s-1 and the spectrum is well-represented by a power-law function with photon index 2.1 +- 0.1. We searched for significant variation of the flux at the spin frequency of the pulsar and for orbital modulation, taking into account the trials due to the uncertainties in the position, the orbital motion of the pulsar and the intrinsic evolution of the pulsar spin. No significant deviation from a constant flux at any time scale was found, preventing a firm identification via time variability. Nonetheless, the association of the LAT source as the gamma-ray counterpart of SAX J1808.4-3658 would match the emission expected from the millisecond pulsar, if it switches on as a rotation-powered source during X-ray quiescence.Comment: 8 pages, 4 figures, accepted by MNRA