http://arxiv.org/abs/0708.2889
Probing Quantum Gravity using Photons from a Mkn 501 Flare Observed by MAGIC
J. Albert, et al., for the MAGIC Collaboration, John Ellis, N.E. Mavromatos, D.V. Nanopoulos, A.S. Sakharov, E.K.G. Sarkisyan
5 pages, 3 figures, submitted to Phys. Rev. Lett
(Submitted on 21 Aug 2007)
"We use the timing of photons observed by the MAGIC gamma-ray telescope during a flare of the active galaxy Markarian 501 to probe a vacuum refractive index ~ 1-(E/M
QGn)
n, n = 1,2, that might be induced by quantum gravity. The peaking of the flare is found to maximize for quantum-gravity mass scales M
QG1 ~ 0.4x10
18 GeV or M
QG2 ~ 0.6x10
11 GeV, and we establish lower limits M
QG1 > 0.26x10
18 GeV or M
QG2 > 0.39x10
11 GeV at the 95% C.L. Monte Carlo studies confirm the MAGIC sensitivity to propagation effects at these levels. Thermal plasma effects in the source are negligible, but we cannot exclude the importance of some other source effect."
http://arxiv.org/abs/0708.2934
Observation of Galactic Sources of Very High Energy Gamma-Rays with the MAGIC Telescope
H. Bartko, for the MAGIC collaboration
Mod. Phys. Lett. A, Vol. 22, No. 29 (2007) pp. 2167-2174
(Submitted on 21 Aug 2007 (v1), last revised 25 Aug 2007 (this version, v2))
"The MAGIC telescope with its 17m diameter mirror is today the largest operating single-dish Imaging Air Cherenkov Telescope (IACT). It is located on the Canary Island La Palma, at an altitude of 2200m above sea level, as part of the Roque de los Muchachos European Northern Observatory. The MAGIC telescope detects celestial very high energy gamma-radiation in the energy band between about 50 GeV and 10 TeV. Since the autumn of 2004 MAGIC has been taking data routinely, observing various objects, like supernova remnants (SNRs), gamma-ray binaries, Pulsars, Active Galactic Nuclei (AGN) and Gamma-ray Bursts (GRB). We briefly describe the observational strategy, the procedure implemented for the data analysis, and discuss the results of observations of Galactic Sources."
http://arxiv.org/abs/0708.3571
MAGIC multiwavelength observations: policy, and some recent results
MAGIC Collaboration: Alessandro De Angelis
5 pages, 5 figures; to be published in the Proceedings The Second Multiwavelength Workshop for Next Generation Gamma-Ray Experiments, Adler Planetarium, Chicago, Illinois, August 9-10, 2007
(Submitted on 27 Aug 2007 (v1), last revised 28 Aug 2007 (this version, v2))
"MAGIC, 17 meters of diameter, is the world's largest single dish Imaging Atmospheric Cherenkov Telescope, and reaches in the analysis the lowest energy threshold (60 GeV) among the VHE gamma detectors. Completed in September 2004, MAGIC started full operation with its first cycle of data taking in February 2005. MAGIC observations in the galaxy cover, among others, supernova remnants, the Galactic Center and binary systems. The low threshold makes of MAGIC the IACT looking deepest in the Universe: the record of extragalactic sources detected includes Active Galactic Nuclei (AGN) at z > 0.2. Here we discuss the present performance of MAGIC and the policy for the use of MAGIC data in multiwavelength campaigns. After a review of some recent highlights from MW studies, including the discovery of the most distant source ever detected (the AGN 3C279 at z = 0.54), we present the expected performance of MAGIC after the inauguration of the second telescope, scheduled for September 21st, 2008. Multiwavelength studies are a key for the study of emission mechanisms from galactic and extragalactic sources, and Very-High Energy photon detectors are becoming crucial as the GLAST era approaches."
http://arxiv.org/abs/astro-ph/0702008
Variable VHE gamma-ray emission from Markarian 501
MAGIC Collaboration, (J. Albert, et al)
51 pages, 28 figures. Submitted to ApJ. Changes with respect to V1: a) More detailed abstract, b)Section 2 (technical details of instrument and analysis) significantly shortened, c) Corrected formula 8, d) Corrected figures 20 and 21, e) Discussion on Quantum Gravity limits is removed f) Corrected some typos in text and added some references
(Submitted on 1 Feb 2007 (v1), last revised 8 Jun 2007 (this version, v2))
"The blazar Markarian 501 (Mrk 501) was observed at energies above 0.10 TeV with the MAGIC telescope from May through July 2005. The high sensitivity of the instrument enabled the determination of the flux and spectrum of the source on a night-by-night basis. Throughout our observational campaign, the flux from Mrk 501 was found to vary by an order of magnitude. Intra-night flux variability with flux-doubling times down to 2 minutes was observed during the two most active nights, namely June 30 and July 9. These are the fastest flux variations ever observed in Mrk 501. The ~20-minute long flare of July 9 showed an indication of a 4 +/- 1 min time delay between the peaks of F(<0.25 TeV) and F(>1.2 TeV), which may indicate a progressive acceleration of electrons in the emitting plasma blob. The flux variability was quantified for several energy ranges, and found to increase with the energy of the gamma-ray photons. The spectra hardened significantly with increasing flux, and during the two most active nights, a spectral peak was clearly detected at 0.43 +/- 0.06 TeV and 0.25 +/- 0.07 TeV, respectively for June 30 and July 9. There is no evidence of such spectral feature for the other nights at energies down to 0.10 TeV, thus suggesting that the spectral peak is correlated with the source luminosity. These observed characteristics could be accommodated in a Synchrotron-Self-Compton (SSC) framework in which the increase in gamma-ray flux is produced by a freshly injected (high energy) electron population."
the next two papers form a pair.
the first, by an eminent European astrophysicist Simon White (director of the Garching MPI for Astrophysics) warned of degradation to his field's creative talent, intelligence and credibility resulting from collaboration with hordes of experimental particle physicists in singleminded quest to detect "dark energy"
the second is a REPLY to Simon White's April paper, from an American astrophysicist Edward W. "Rocky" Kolb.
He is director of Particle Astrophysics Center at Fermilab, and led a joint Dark Energy Task Force made up of astrophysicists and particle physicists commissioned to advise the DOE, NSF, and NASA. Here is the task force report:
http://arxiv.org/abs/astro-ph/0609591
http://arxiv.org/abs/0704.2291
Fundamentalist physics: why Dark Energy is bad for Astronomy
Simon D.M. White
Essay commissioned for publication in
Reports on Progress in Physics. 19 pages including 3 figures
(Submitted on 18 Apr 2007)
"Astronomers carry out observations to explore the diverse processes and objects which populate our Universe. High-energy physicists carry out experiments to approach the Fundamental Theory underlying space, time and matter. Dark Energy is a unique link between them, reflecting deep aspects of the Fundamental Theory, yet apparently accessible only through astronomical observation. Large sections of the two communities have therefore converged in support of astronomical projects to constrain Dark Energy. In this essay I argue that this convergence can be damaging for astronomy. The two communities have different methodologies and different scientific cultures. By uncritically adopting the values of an alien system, astronomers risk undermining the foundations of their own current success and endangering the future vitality of their field. Dark Energy is undeniably an interesting problem to attack through astronomical observation, but it is one of many and not necessarily the one where significant progress is most likely to follow a major investment of resources."
http://arxiv.org/abs/0708.1199
A Thousand Invisible Cords Binding Astronomy and High-Energy Physics
Rocky Kolb (Department of Astronomy & Astrophysics, The Enrico Fermi Institute, and The Kavli Institute for Cosmological Physics, The University of Chicago)
Why "Fundamentalist" Physics Is Good for Astronomy (in response to the paper of Simon White,
http://arxiv.org/abs/0704.2291
(Submitted on 9 Aug 2007)
"The traditional realm of astronomy is the observation and study of the largest objects in the Universe, while the traditional domain of high-energy physics is the study of the smallest things in nature. But these two sciences concerned with opposite ends of the size spectrum are, in Muir's words, bound fast by a thousand invisible cords that cannot be broken. In this essay I propose that collaborations of astronomers and high-energy physicists on common problems are beneficial for both fields, and that both astronomy and high-energy physics can advance by this close and still growing relationship. Dark matter and dark energy are two of the binding cords I will use to illustrate how collaborations of astronomers and high-energy physicists on large astronomical projects can be good for astronomy, and how discoveries in astronomy can guide high-energy physicists in their quest for understanding nature on the smallest scales. Of course, the fields have some different intellectual and collaborative traditions, neither of which is ideal. The cultures of the different fields cannot be judged to be right or wrong; they either work or they don't. When astronomers and high-energy physicists work together, the binding cords can either encourage or choke creativity. The challenge facing the astronomy and high-energy physics communities is to adopt the best traditions of both fields. It is up to us to choose wisely."
