43 research outputs found
New Constraints on Hidden Photons using Very High Energy Gamma-Rays from the Crab Nebula
Extensions of the standard model of particle physics, in particular those
based on string theory, often predict a new U(1) gauge symmetry in a hidden
sector. The corresponding gauge boson, called hidden photon, naturally
interacts with the ordinary photon via gauge kinetic mixing, leading to photon
- hidden photon oscillations. In this framework, one expects photon
disappearance as a function of the mass of the hidden photon and the mixing
angle, loosely constrained from theory. Several experiments have been carried
out or are planned to constrain the mass-mixing plane.
In this contribution we derive new constraints on the hidden photon
parameters, using very high energy gamma-rays detected from the Crab Nebula,
whose broad-band spectral characteristics are well understood. The very high
energy gamma-ray observations offer the possibility to provide bounds in a
broad mass range at a previously unexplored energy and distance scale. Using
existing data that were taken with several Cherenkov telescopes, we discuss our
results in the context of current constraints and consider the possibilities of
using astrophysical data to search for hidden photon signatures.Comment: Proceedings of the "Heidelberg International Symposium on High Energy
Gamma-Ray Astronomy", Heidelberg, Germany, July 7-11, 2008, submitted to AIP
Conference Proceedings. 4 pages, 2 figures, 1 tabl
Time-dependent absorption of very high-energy gamma-rays from the Galactic center by pair-production
Very high energy (VHE) gamma-rays have been detected from the direction of
the Galactic center. The H.E.S.S. Cherenkov telescopes have located this
gamma-ray source with a preliminary position uncertainty of 8.5" per axis (6"
statistic + 6" sytematic per axis). Within the uncertainty region several
possible counterpart candidates exist: the Super Massive Black Hole Sgr A*, the
Pulsar Wind Nebula candidate G359.95-0.04, the Low Mass X-Ray Binary-system
J174540.0-290031, the stellar cluster IRS 13, as well as self-annihilating dark
matter. It is experimentally very challenging to further improve the positional
accuracy in this energy range and therefore, it may not be possible to clearly
associate one of the counterpart candidates with the VHE-source. Here, we
present a new method to investigate a possible link of the VHE-source with the
near environment of Sgr A* (within approximately 1000 Schwarzschild radii).
This method uses the time- and energy-dependent effect of absorption of
gamma-rays by pair-production (in the following named pair-eclipse) with
low-energy photons of stars closely orbiting the SMBH Sgr A*.Comment: 4 pages, 6 figures, Published in Proceedings of the 4th International
Meeting on High Energy Gamma-Ray Astronomy (Gamma 08), Heidelber
Future mmVLBI Research with ALMA: A European vision
Very long baseline interferometry at millimetre/submillimetre wavelengths
(mmVLBI) offers the highest achievable spatial resolution at any wavelength in
astronomy. The anticipated inclusion of ALMA as a phased array into a global
VLBI network will bring unprecedented sensitivity and a transformational leap
in capabilities for mmVLBI. Building on years of pioneering efforts in the US
and Europe the ongoing ALMA Phasing Project (APP), a US-led international
collaboration with MPIfR-led European contributions, is expected to deliver a
beamformer and VLBI capability to ALMA by the end of 2014 (APP: Fish et al.
2013, arXiv:1309.3519).
This report focuses on the future use of mmVLBI by the international users
community from a European viewpoint. Firstly, it highlights the intense science
interest in Europe in future mmVLBI observations as compiled from the responses
to a general call to the European community for future research projects. A
wide range of research is presented that includes, amongst others:
- Imaging the event horizon of the black hole at the centre of the Galaxy
- Testing the theory of General Relativity an/or searching for alternative
theories
- Studying the origin of AGN jets and jet formation
- Cosmological evolution of galaxies and BHs, AGN feedback
- Masers in the Milky Way (in stars and star-forming regions)
- Extragalactic emission lines and astro-chemistry
- Redshifted absorption lines in distant galaxies and study of the ISM and
circumnuclear gas
- Pulsars, neutron stars, X-ray binaries
- Testing cosmology
- Testing fundamental physical constantsComment: Replaced figures 2 and 3: corrected position SRT. Corrected minor
typo in 5.
Joint Observation of the Galactic Center with MAGIC and CTA-LST-1
MAGIC is a system of two Imaging Atmospheric Cherenkov Telescopes (IACTs), designed to detect very-high-energy gamma rays, and is operating in stereoscopic mode since 2009 at the Observatorio del Roque de Los Muchachos in La Palma, Spain. In 2018, the prototype IACT of the Large-Sized Telescope (LST-1) for the Cherenkov Telescope Array, a next-generation ground-based gamma-ray observatory, was inaugurated at the same site, at a distance of approximately 100 meters from the MAGIC telescopes. Using joint observations between MAGIC and LST-1, we developed a dedicated analysis pipeline and established the threefold telescope system via software, achieving the highest sensitivity in the northern hemisphere. Based on this enhanced performance, MAGIC and LST-1 have been jointly and regularly observing the Galactic Center, a region of paramount importance and complexity for IACTs. In particular, the gamma-ray emission from the dynamical center of the Milky Way is under debate. Although previous measurements suggested that a supermassive black hole Sagittarius A* plays a primary role, its radiation mechanism remains unclear, mainly due to limited angular resolution and sensitivity. The enhanced sensitivity in our novel approach is thus expected to provide new insights into the question. We here present the current status of the data analysis for the Galactic Center joint MAGIC and LST-1 observations
Broadband Multi-wavelength Properties of M87 during the 2017 Event Horizon Telescope Campaign
Abstract: In 2017, the Event Horizon Telescope (EHT) Collaboration succeeded in capturing the first direct image of the center of the M87 galaxy. The asymmetric ring morphology and size are consistent with theoretical expectations for a weakly accreting supermassive black hole of mass ∼6.5 × 109 M ⊙. The EHTC also partnered with several international facilities in space and on the ground, to arrange an extensive, quasi-simultaneous multi-wavelength campaign. This Letter presents the results and analysis of this campaign, as well as the multi-wavelength data as a legacy data repository. We captured M87 in a historically low state, and the core flux dominates over HST-1 at high energies, making it possible to combine core flux constraints with the more spatially precise very long baseline interferometry data. We present the most complete simultaneous multi-wavelength spectrum of the active nucleus to date, and discuss the complexity and caveats of combining data from different spatial scales into one broadband spectrum. We apply two heuristic, isotropic leptonic single-zone models to provide insight into the basic source properties, but conclude that a structured jet is necessary to explain M87’s spectrum. We can exclude that the simultaneous γ-ray emission is produced via inverse Compton emission in the same region producing the EHT mm-band emission, and further conclude that the γ-rays can only be produced in the inner jets (inward of HST-1) if there are strongly particle-dominated regions. Direct synchrotron emission from accelerated protons and secondaries cannot yet be excluded
Data from Lineage Tracing of Human B Cells Reveals the In Vivo Landscape of Human Antibody Class Switching
Data from Lineage Tracing of Human B Cells Reveals the In Vivo Landscape of Human Antibody Class Switchin
Cloning antibodies from single cells in pooled sequence libraries by selective PCR.
Antibodies function by binding to antigens. Antibodies must be cloned and expressed to determine their binding characteristics, but current methods for high-throughput antibody sequencing yield antibody DNA pooled from many cells and do not readily permit cloning of antibodies from single B cells. We present a strategy for retrieving and cloning antibody DNA from single cells within a pooled library of cells. Our strategy, called selective PCR for antibody retrieval (SPAR), takes advantage of the unique sequence barcodes attached to individual cDNA molecules during sample preparation to enable specific amplification by PCR of antibody heavy- and light-chain cDNA originating from a single cell. We show through computational analysis that most human antibodies sequenced using typical high-throughput methods can be retrieved using SPAR, and experimentally demonstrate retrieval of full-length antibody variable region cDNA from three cells within pools of ~5,000 cells. SPAR enables rapid low-cost cloning and expression of native human antibodies from pooled single-cell sequence libraries for functional characterization