236 research outputs found
Orthodontic tooth movement in the prednisolone-treated rat
Adverse effects of corticosteroids on bone metabolism raise concerns as to whether steroid treatment may influence orthodontic movement. This study examined the effect of prednisolone on orthodontic movement using an established rat model. The corticosteroid treated group (N = 6) was administered prednisolone (1 mg/kg) daily, for a 12-day induction period; the control group (N = 6) received equivalent volumes of saline. On day 12, an orthodontic appliance was placed which exerted 30 g of mesial force to the maxillary first molar. Animals were sacrificed on day 24 and tooth movement was measured. Sagittal sections of the molars were stained with haematoxylin and eosin, and for tartrate-resistant acid phosphatase (TRAP) activity. While there were no significant differences in the magnitude of tooth movement between the 2 groups, steroid-treated rats displayed significantly less root resorption on the compression side and fewer TRAP-positive cells within the PDL space on the same side. This suggests steroid treatment suppressed elastic activity
Probing the origin of VHE emission from M 87 with MWL observations in 2010
The large majority of extragalactic very high energy (VHE; E>100 GeV) sources
belongs to the class of active galactic nuclei (AGN), in particular the BL Lac
sub-class. AGNs are characterized by an extremely bright and compact emission
region, powered by a super-massive black hole (SMBH) and an accretion disk, and
relativistic outflows (jets) detected all across the electro-magnetic spectrum.
In BL Lac sources the jet axis is oriented close to the line of sight, giving
rise to a relativistic boosting of the emission. In radio galaxies, on the
other hand, the jet makes a larger angle to the line of sight allowing to
resolve the central core and the jet in great details. The giant radio galaxy M
87 with its proximity (1 6Mpc) and its very massive black hole ((3-6) x 10^9
M_solar) provides a unique laboratory to investigate VHE emission in such
objects and thereby probe particle acceleration to relativistic energies near
SMBH and in jets. M 87 has been established as a VHE emitter since 2005. The
VHE emission displays strong variability on time-scales as short as a day. It
has been subject of a large joint VHE and multi-wavelength (MWL) monitoring
campaign in 2008, where a rise in the 43 GHz VLBA radio emission of the
innermost region (core) was found to coincide with a flaring activity at VHE.
This had been interpreted as a strong indication that the VHE emission is
produced in the direct vicinity of the SMBH black hole. In 2010 again a flare
at VHE was detected triggering further MWL observations with the VLBA, Chandra,
and other instruments. At the same time M 87 was also observed with the
Fermi-LAT telescope at GeV energies and the European VLBI Network (EVN). In
this contribution preliminary results from the campaign will be presented.Comment: 5 pages, 2 figures, in the proceedings of the "International Workshop
on Beamed and Unbeamed Gamma-Rays from Galaxies" 11-15 April 2011, Lapland
Hotel Olos, Muonio, Finland, Journal of Physics: Conference Series Volume
355, 201
Significant Biochemical, Biophysical and Metabolic Diversity in Circulating Human Cord Blood Reticulocytes
10.1371/journal.pone.0076062PLoS ONE810-POLN
VERITAS Observations of the gamma-Ray Binary LS I +61 303
LS I +61 303 is one of only a few high-mass X-ray binaries currently detected
at high significance in very high energy gamma-rays. The system was observed
over several orbital cycles (between September 2006 and February 2007) with the
VERITAS array of imaging air-Cherenkov telescopes. A signal of gamma-rays with
energies above 300 GeV is found with a statistical significance of 8.4 standard
deviations. The detected flux is measured to be strongly variable; the maximum
flux is found during most orbital cycles at apastron. The energy spectrum for
the period of maximum emission can be characterized by a power law with a
photon index of Gamma=2.40+-0.16_stat+-0.2_sys and a flux above 300 GeV
corresponding to 15-20% of the flux from the Crab Nebula.Comment: accepted for publication in The Astrophysical Journa
VERITAS Observations of the BL Lac Object 1ES 1218+304
The VERITAS collaboration reports the detection of very-high-energy (VHE)
gamma-ray emission from the high-frequency-peaked BL Lac object 1ES 1218+304
located at a redshift of z=0.182. A gamma-ray signal was detected with high
statistical significance for the observations taken during several months in
the 2006-2007 observing season. The photon spectrum between ~160 GeV and ~1.8
TeV is well described by a power law with an index of Gamma = 3.08 +/-
0.34(stat) +/- 0.2(sys). The integral flux above 200 GeV corresponds to ~6% of
that of the Crab Nebula. The light curve does not show any evidence for VHE
flux variability. Using lower limits on the density of the extragalactic
background light (EBL) in the near-IR to mid-IR we are able to limit the range
of intrinsic energy spectra for 1ES 1218+304. We show that the intrinsic photon
spectrum is harder than a power law with an index of Gamma = 2.32 +/- 0.37.
When including constraints from the spectra of 1ES 1101-232 and 1ES 0229+200,
the spectrum of 1ES 1218+304 is likely to be harder than Gamma = 1.86 +/- 0.37.Comment: Submitted to Proceedings of "4th Heidelberg International Symposium
on High Energy Gamma-Ray Astronomy 2008
Status of the VERITAS Observatory
VERITAS, an Imaging Atmospheric Cherenkov Telescope (IACT) system for
gammma-ray astronomy in the GeV-TeV range, has recently completed its first
season of observations with a full array of four telescopes. A number of
astrophysical gamma-ray sources have been detected, both galactic and
extragalactic, including sources previously unknown at TeV energies. We
describe the status of the array and some highlight results, and assess the
technical performance, sensitivity and shower reconstruction capabilities.Comment: Submitted to Proceedings of "4th Heidelberg International Symposium
on High Energy Gamma-Ray Astronomy 2008
A connection between star formation activity and cosmic rays in the starburst galaxy M 82
Although Galactic cosmic rays (protons and nuclei) are widely believed to be
dominantly accelerated by the winds and supernovae of massive stars, definitive
evidence of this origin remains elusive nearly a century after their discovery
[1]. The active regions of starburst galaxies have exceptionally high rates of
star formation, and their large size, more than 50 times the diameter of
similar Galactic regions, uniquely enables reliable calorimetric measurements
of their potentially high cosmic-ray density [2]. The cosmic rays produced in
the formation, life, and death of their massive stars are expected to
eventually produce diffuse gamma-ray emission via their interactions with
interstellar gas and radiation. M 82, the prototype small starburst galaxy, is
predicted to be the brightest starburst galaxy in gamma rays [3, 4]. Here we
report the detection of >700 GeV gamma rays from M 82. From these data we
determine a cosmic-ray density of 250 eV cm-3 in the starburst core of M 82, or
about 500 times the average Galactic density. This result strongly supports
that cosmic-ray acceleration is tied to star formation activity, and that
supernovae and massive-star winds are the dominant accelerators.Comment: 18 pages, 4 figures; published in Nature; Version is prior to
Nature's in-house style editing (differences are minimal
Discovery of Very High-Energy Gamma-Ray Radiation from the BL Lac 1ES 0806+524
The high-frequency-peaked BL-Lacertae object \objectname{1ES 0806+524}, at
redshift z=0.138, was observed in the very-high-energy (VHE) gamma-ray regime
by VERITAS between November 2006 and April 2008. These data encompass the two-,
and three-telescope commissioning phases, as well as observations with the full
four-telescope array. \objectname{1ES 0806+524} is detected with a statistical
significance of 6.3 standard deviations from 245 excess events. Little or no
measurable variability on monthly time scales is found. The photon spectrum for
the period November 2007 to April 2008 can be characterized by a power law with
photon index between
300 GeV and 700 GeV. The integral flux above 300 GeV is
which corresponds to 1.8% of the Crab Nebula flux. Non contemporaneous
multiwavelength observations are combined with the VHE data to produce a
broadband spectral energy distribution that can be reasonably described using a
synchrotron-self Compton model.Comment: 14 pages, 4 figures, accepted to APJ
A search for spectral hysteresis and energy-dependent time lags from X-ray and TeV gamma-ray observations of Mrk 421
Blazars are variable emitters across all wavelengths over a wide range of
timescales, from months down to minutes. It is therefore essential to observe
blazars simultaneously at different wavelengths, especially in the X-ray and
gamma-ray bands, where the broadband spectral energy distributions usually
peak.
In this work, we report on three "target-of-opportunity" (ToO) observations
of Mrk 421, one of the brightest TeV blazars, triggered by a strong flaring
event at TeV energies in 2014. These observations feature long, continuous, and
simultaneous exposures with XMM-Newton (covering X-ray and optical/ultraviolet
bands) and VERITAS (covering TeV gamma-ray band), along with contemporaneous
observations from other gamma-ray facilities (MAGIC and Fermi-LAT) and a number
of radio and optical facilities. Although neither rapid flares nor significant
X-ray/TeV correlation are detected, these observations reveal subtle changes in
the X-ray spectrum of the source over the course of a few days. We search the
simultaneous X-ray and TeV data for spectral hysteresis patterns and time
delays, which could provide insight into the emission mechanisms and the source
properties (e.g. the radius of the emitting region, the strength of the
magnetic field, and related timescales). The observed broadband spectra are
consistent with a one-zone synchrotron self-Compton model. We find that the
power spectral density distribution at Hz from the
X-ray data can be described by a power-law model with an index value between
1.2 and 1.8, and do not find evidence for a steepening of the power spectral
index (often associated with a characteristic length scale) compared to the
previously reported values at lower frequencies.Comment: 45 pages, 15 figure
Multiwavelength Observations of LS I +61 303 with VERITAS, Swift and RXTE
We present results from a long-term monitoring campaign on the TeV binary LSI
+61 303 with VERITAS at energies above 500 GeV, and in the 2-10 keV hard X-ray
bands with RXTE and Swift, sampling nine 26.5 day orbital cycles between
September 2006 and February 2008. The binary was observed by VERITAS to be
variable, with all integrated observations resulting in a detection at the 8.8
sigma (2006/2007) and 7.3 sigma (2007/2008) significance level for emission
above 500 GeV. The source was detected during active periods with flux values
ranging from 5 to 20% of the Crab Nebula, varying over the course of a single
orbital cycle. Additionally, the observations conducted in the 2007-2008
observing season show marginal evidence (at the 3.6 sigma significance level)
for TeV emission outside of the apastron passage of the compact object around
the Be star. Contemporaneous hard X-ray observations with RXTE and Swift show
large variability with flux values typically varying between 0.5 and 3.0*10^-11
ergs cm^-2 s^-1 over a single orbital cycle. The contemporaneous X-ray and TeV
data are examined and it is shown that the TeV sampling is not dense enough to
detect a correlation between the two bands.Comment: 30 pages, 5 figures, 2 table, Accepted for publication in The
Astrophysical Journa
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