We report on variability and correlation studies using multiwavelength observations of the blazar Mrk 421 during the month of 2010 February, when an extraordinary flare reaching a level of ∼27 Crab ...Units above 1 TeV was measured in very high energy (VHE) γ-rays with the Very Energetic Radiation Imaging Telescope Array System (VERITAS) observatory. This is the highest flux state for Mrk 421 ever observed in VHE γ-rays. Data are analyzed from a coordinated campaign across multiple instruments, including VHE γ-ray (VERITAS, Major Atmospheric Gamma-ray Imaging Cherenkov), high-energy γ-ray (Fermi-LAT), X-ray (Swift, Rossi X-ray Timing Experiment, MAXI), optical (including the GASP-WEBT collaboration and polarization data), and radio (Metsähovi, Owens Valley Radio Observatory, University of Michigan Radio Astronomy Observatory). Light curves are produced spanning multiple days before and after the peak of the VHE flare, including over several flare "decline" epochs. The main flare statistics allow 2 minute time bins to be constructed in both the VHE and optical bands enabling a cross-correlation analysis that shows evidence for an optical lag of ∼25-55 minutes, the first time-lagged correlation between these bands reported on such short timescales. Limits on the Doppler factor (δ 33) and the size of the emission region ( ) are obtained from the fast variability observed by VERITAS during the main flare. Analysis of 10 minute binned VHE and X-ray data over the decline epochs shows an extraordinary range of behavior in the flux-flux relationship, from linear to quadratic to lack of correlation to anticorrelation. Taken together, these detailed observations of an unprecedented flare seen in Mrk 421 are difficult to explain with the classic single-zone synchrotron self-Compton model.
We report on the results from the observations in the very high energy band (VHE; unk greater than or equal to 100 GeV) of the black hole X-ray binary (BHXB) Cygnus X-1. The observations were ...performed with the MAGIC telescope, for a total of 40 hr during 26 nights, spanning the period between 2006 June and November. Searches for steady Y-ray signals yielded no positive result, and upper limits to the integral flux ranging between 1% and 2% of the Crab Nebula flux, depending on the energy, have been established. We also analyzed each observation night independently, obtaining evidence of Y-ray signals at the 4.0 sigma significance level (3.2 sigma after trial correction) for 154 minutes of effective on-time (EOT) on September 24 between 20:58 and 23:41 UTC, coinciding with an X-ray flare seen by RXTE, Swift, and INTEGRAL. A search for faster-varying signals within a night resulted in an excess with a significance of 4.9 sigma (4.1 sigma after trial correction) for 79 minutes EOT between 22:17 and 23:41 UTC. The measured excess is compatible with a pointlike source at the position of Cygnus X-1 and excludes the nearby radio nebula powered by its relativistic jet. The differential energy spectrum is well fitted by an unbroken power law described as dN/(dA dt dE) = (2.3 plus or minus 0.6) x 10- super(12)(E/1TeV) super(-3.2 plus or minus 0.6). This is the first experimental evidence of VHE emission from a stellar mass black hole and therefore from a confirmed accreting X-ray binary.
Summary
This study compared the effects of pediatric acne treatment with two isotretinoin formulations on bone mineral density. We demonstrated no difference in the effect of the two formulations. No ...effect on pediatric bone mineral density was identified for either formulation.
Introduction
Isotretinoin (13-cis-retinoic acid) is a treatment for recalcitrant nodular acne with a purported effect on bone mineral density (BMD). The side effects of isotretinoin on vertebral bone were evaluated to assess the safety of a new FDA-approved isotretinoin formulation: Lidose-isotretinoin (Cip-Iso).
Methods
This double-blind, randomized, phase III, active control, parallel-group, multicenter study compared the safety, efficacy, and non-inferiority of CIP-Iso to a marketed reference product, Accutane®, in severe recalcitrant nodular acne subjects. Three hundred fifty-eight pediatric male and female subjects aged between 12 and 17 years underwent 20 weeks of treatment with PA lumbar spine dual X-ray absorptiometry (DXA) measurements obtained for bone mineral density (BMD) and Z-scores, 5.5 months apart on visits 1 and 8. One hundred sixty-eight of 358 subjects had height adjusted Z-scores (HAZ) calculated.
Results
There was no difference in the least squares (LS) mean Z-score or HAZ of the two drugs at visit 1 or 8. The mean and LS mean Z-score and HAZ were greater than zero at visits 1 and 8 for both drugs. The change in the LS mean spine Z-score, but not HAZ, between visits, was statistically significant for both drugs. There was a mean increase in BMD (g/cm
2
) for both products between visits.
Conclusions
There is no difference in the effect of two formulations of isotretinoin on spine bone density after 6 months of treatment. BMD increased and the small change in spine Z-score over treatment disappeared after height adjustment. Mean positive Z-scores and HAZ in the study were likely due to the exclusion of low and inclusion of high Z-score subjects.
The variability of the blazar Markarian 421 in TeV gamma rays over a 14-year time period has been explored with the Whipple 10m telescope. It is shown that the dynamic range of its flux variations is ...large and similar to that in X-rays. A correlation between the X-ray and TeV energy bands is observed during some bright flares and when the complete data sets are binned on long timescales. The main database consists of 878.4h of observation with the Whipple telescope, spread over 783 nights. The peak energy response of the telescope was 400GeV with 20% uncertainty. This is the largest database of any TeV-emitting active galactic nucleus (AGN) and hence was used to explore the variability profile of Markarian 421. The time-averaged flux from Markarian 421 over this period was 0.446±0.008Crab flux units. The flux exceeded 10Crab flux units on three separate occasions. For the 2000–2001 season the average flux reached 1.86Crab units, while in the 1996–1997 season the average flux was only 0.23Crab units.
The Cherenkov light flashes produced by extensive air showers are very short in time. A high bandwidth and fast digitizing readout, therefore, can minimize the influence of the background from the ...light of the night sky, and improve the performance in Cherenkov telescopes. The time structure of the Cherenkov image can further be used in single-dish Cherenkov telescopes as an additional parameter to reduce the background from unwanted hadronic showers. A description of an analysis method which makes use of the time information and the subsequent improvement on the performance of the MAGIC telescope (especially after the upgrade with an ultra fast 2 GSamples/s digitization system in February 2007) will be presented. The use of timing information in the analysis of the new MAGIC data reduces the background by a factor two, which in turn results in an enhancement of about a factor 1.4 of the flux sensitivity to point-like sources, as tested on observations of the Crab Nebula.
The MAGIC collaboration has studied the high-frequency-peaked BL Lac object 1ES 1218+30.4, at a redshift z = 0.182, using the MAGIC imaging air Cerenkov telescope located on the Canary Island of La ...Palma. A gamma-ray signal was observed with 6.4 s significance. The differential energy spectrum for an energy threshold of 120 GeV can be fitted by a simple power law, yielding F sub(E)(E) = (8.1 c 2.1) x 10 super(-7) E/(250 GeV) super(-3.0c0.4) TeV super(-1) m super(-2) s super(-1). During the 6 days of observation in 2005 January, no time variability on timescales of days was found within the statistical errors. The observed integral flux above 350 GeV is nearly a factor of 2 below the upper limit reported by the Whipple collaboration in 2003.
During its first data cycle, between 2005 and the beginning of 2006, the fast repositioning system of the MAGIC telescope allowed the observation of nine different gamma-ray bursts as possible ...sources of very high energy gamma -rays. These observations were triggered by alerts from Swift, HETE-2, and INTEGRAL; they started as quickly as possible after the alerts and lasted for several minutes, with an energy threshold varying between 80 and 200 GeV, depending on the zenith angle of the burst. No evidence for gamma signals was found, and upper limits for the flux were derived for all events using the standard analysis chain of MAGIC. For the bursts with measured redshifts, the upper limits are compatible with a power-law extrapolation, when the intrinsic fluxes are evaluated taking into account the attenuation due to the scattering in the metagalactic radiation field.
Abstract Objectives To determine the efficacy of hybrid external fixation in the treatment of tibial pilon fractures. Design Retrospective, multicentre study. Patients/Participants Adult patients ...with tibial pilon fractures treated with hybrid external fixation. Intervention Fracture reduction with ligamentotaxis and fixation with XCaliber hybrid external fixator. Main outcome measurements Fracture union, complications, functional outcome (Mazur Ankle Score). Results Union was obtained in 159 fractures at an average of 125 days; there were three delayed unions and three non-unions. The most frequent complication was superficial pin‐track infections (48), all of which responded to local wound care and antibiotics. There were no deep infections and no DVT. Only one fracture had loss of reduction that required frame revision. The overall functional scores were 91 (excellent) for AO/OTA type A fractures, 89 (good) for type B fractures, and 75 (satisfactory) for type C fractures. Conclusions Hybrid external fixation is an effective method of stabilising tibial pilon fractures, particularly those with marked comminution. The minimally‐invasive technique and stable fixation enable early mobilisation, with good functional results and minimal complications. Level of evidence Level IV Case series.
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