scholarly journals Advances from Recent Multi-wavelength Campaigns on Sgr A*

2016 ◽  
Vol 11 (S322) ◽  
pp. 1-10
Author(s):  
Daryl Haggard
Keyword(s):  
Gravitational Lensing ◽  
Electromagnetic Spectrum ◽  
Physical Processes ◽  
Time Resolved ◽  
X Ray ◽  
Sagittarius A ◽  
Near Ir ◽  
The Status ◽  
Multi Wavelength ◽  
Sgr A

AbstractSagittarius A* is the closest example of a supermassive black hole and our proximity allows us to detect emission from its accretion flow in the radio, submillimeter, near IR, and X-ray regimes. Ambitious monitoring campaigns have yielded rich multi-wavelength, time-resolved data that have the power to probe the physical processes underlying Sgr A*’s quiescent and flare emission. Here, I review the status of Sgr A* X-ray monitoring campaigns from the Chandra X-ray Observatory (also XMM Newton, and Swift), and efforts to coordinate these with observations across the electromagnetic spectrum. I also discuss how these observations constrain models for Sgr A*’s variability, which range from tidal disruption of asteroids to gravitational lensing to collimated outflows to magnetic reconnection.

scholarly journals Statistical and theoretical studies of flares from Sagittarius A⋆

2016 ◽  
Vol 11 (S322) ◽  
pp. 31-38
Author(s):  
Ya-Ping Li ◽  
Qiang Yuan ◽  
Q. Daniel Wang ◽  
P. F. Chen ◽  
Joseph Neilsen ◽  
...  
Keyword(s):  
Black Hole ◽  
Solar Flares ◽  
Galactic Center ◽  
Theoretical Models ◽  
Spatial Dimension ◽  
X Ray ◽  
Sagittarius A ◽  
Multi Wavelength ◽  
Self Organized Criticality ◽  
Sgr A

AbstractMulti-wavelength flares have routinely been observed from the supermassive black hole, Sagittarius A⋆ (Sgr A⋆), at our Galactic center. The nature of these flares remains largely unclear, despite many theoretical models. We study the statistical properties of the Sgr A⋆ X-ray flares and find that they are consistent with the theoretical prediction of the self-organized criticality system with the spatial dimension S = 3. We suggest that the X-ray flares represent plasmoid ejections driven by magnetic reconnection (similar to solar flares) in the accretion flow onto the black hole. Motivated by the statistical results, we further develop a time-dependent magnetohydrodynamic (MHD) model for the multi-band flares from Sgr A⋆ by analogy with models of solar flares/coronal mass ejections (CMEs). We calculate the X-ray, infrared flare light curves, and the spectra, and find that our model can explain the main features of the flares.

Large Astronomical Surveys, Catalogs and Databases

2012 ◽  
Vol 21 (3) ◽  
Author(s):  
A. M. Mickaelian
Keyword(s):  
Open Access ◽  
Gamma Ray ◽  
Electromagnetic Spectrum ◽  
Fast Analysis ◽  
X Ray ◽  
Astronomical Surveys ◽  
Radio Range ◽  
The Status ◽  
Cross Correlations ◽  
Stored Information

AbstractWe review the status of all-sky and large astronomical surveys and their catalogued data over the whole range of electromagnetic spectrum, from gamma-ray to radio, such as ROSAT in X-ray, GALEX in UV, SDSS and several POSS1/2 based catalogs (APM, MAPS, USNO, GSC) in optical, 2MASS and WISE in NIR, IRAS and AKARI in MIR/FIR, NVSS and FIRST in radio range and others. Present astronomical archives contain billions of objects, Galactic as well as extragalactic, and the vast amount of data in them permit new studies and discoveries. Cross-correlations result in revealing new objects and new samples. Very often, dozens of thousands of sources hide a few very interesting ones that are needed to be discovered by comparison of various physical characteristics. Most of the modern databases currently provide VO access to the stored information. This permits not only open access but also fast analysis and managing of these data.

scholarly journals A multi-wavelength campaign to study giant pulses from the Crab Pulsar

2012 ◽  
Vol 8 (S291) ◽  
pp. 322-322 ◽  
Author(s):  
Walid Majid
Keyword(s):  
Gamma Ray ◽  
Correlation Study ◽  
Crab Pulsar ◽  
X Ray ◽  
Frequency Detection ◽  
Giant Pulses ◽  
Upper Limit ◽  
The Status ◽  
Multi Wavelength ◽  
Flux Increase

AbstractWe are currently undertaking a monitoring campaign with NASA 70-m antennas to capture a large sample of Crab Giant Pulses (CGP) at multiple radio wavelengths. The goal of this campaign is to carry out a correlation study of CGPs at radio frequencies with pulsed emission from the Crab pulsar with Fermi photons at X-ray. After a year of this study, we expect around 200 Fermi photons to coincide with a CGP radio-frequency detection, allowing us to either confirm a predicted correlation in average gamma-ray pulsed flux increase with GP emission, or place a tight upper limit, at least a factor of 10 more constraining than previous work. We will report on the status of this campaign and will present our preliminary results and prospects for future improvements in receivers and back-end instrumentation.

scholarly journals X-ray Studies of Planetary Nebulae

2016 ◽  
Vol 12 (S323) ◽  
pp. 104-108
Author(s):  
Rodolfo Montez
Keyword(s):  
Mass Transfer ◽  
Planetary Nebulae ◽  
Central Star ◽  
Electromagnetic Spectrum ◽  
Stellar Winds ◽  
X Ray ◽  
New Directions ◽  
Multi Wavelength ◽  
Formation And Evolution ◽  
Compact Sources

AbstractX-ray emission from planetary nebulae (PNe) provides unique insight on the formation and evolution of PNe. Past observations and the ongoing Chandra Planetary Nebulae Survey (ChanPlaNS) provide a consensus on the two types of X-ray emission detected from PNe: extended and compact point-like sources. Extended X-ray emission arises from a shocked “hot bubble” plasma that resides within the nebular shell. Cooler than expected hot bubble plasma temperatures spurred a number of potential solutions with one emerging as the likely dominate process. The origin of X-ray emission from compact sources at the location of the central star is less clear. These sources might arise from one or combinations of the following processes: self-shocking stellar winds, spun-up binary companions, and/or accretion, perhaps from mass transfer, PN fallback, or debris disks. In the discovery phase, X-ray studies of PNe have mainly focused on the origin of the various emission processes. New directions incorporate multi-wavelength observations to study the influence of X-ray emission on the rest of the electromagnetic spectrum.

Some topical issues in research on short-pulse laser-produced plasmas

1980 ◽  
Vol 298 (1439) ◽  
pp. 351-364 ◽  
Keyword(s):  
Recent Work ◽  
Pulse Laser ◽  
Short Pulse ◽  
Fast Time ◽  
Physical Processes ◽  
Time Resolved ◽  
X Ray ◽  
Short Pulse Laser ◽  
Laser Facility ◽  
Interaction Phenomena

A brief review is presented of the main physical processes in laser-produced plasmas. This is followed by illustrations taken from recent work at the S.R.C. Central Laser Facility of the use of X-ray and visible streak cameras for fast time resolved measurements of implosion and interaction phenomena in laser-produced plasmas.

scholarly journals Exploring plasma evolution during Sagittarius A* flares

2013 ◽  
Vol 9 (S303) ◽  
pp. 293-297
Author(s):  
S. Dibi ◽  
S. Markoff ◽  
R. Belmont ◽  
J. Malzac ◽  
N. M. Barrière ◽  
...  
Keyword(s):  
Particle Distribution ◽  
Magnetized Plasma ◽  
Flare Event ◽  
X Ray ◽  
Sagittarius A ◽  
Self Consistent ◽  
Infra Red ◽  
Sgr A ◽  
The Magnetic Field ◽  
Specific Particle

AbstractWe present a new way of describing the flares occurring from Sgr A* within a single zone with a self-consistent calculation of the particle distribution. The results allow us to give an interpretation to the flaring events generated very close to the supermassive black hole (SMBH) without assuming a specific particle distribution. We conclude that the flare data are more likely generated by a weakly magnetized plasma in which the particles flow in and out as expected from an accretion flow. Such a plasma, with prescription for non-thermal acceleration, injection, escape, and cooling losses, gives a spectrum with a break between the infra-red and the X-ray, allowing a better simultaneous match in the different wavelengths. The parameters favor the non-thermal synchrotron spectrum, and a decrease/increase of the magnetic field and plasma density are not favored for producing the flare event, but particle acceleration must be happening by other means. We show that under certain conditions, the real particle distribution can differ significantly from the standard distributions used in such studies.

scholarly journals A decade of transitional millisecond pulsars

2017 ◽  
Vol 13 (S337) ◽  
pp. 47-51 ◽  
Author(s):  
Amruta Jaodand ◽  
Jason W. T. Hessels ◽  
Anne Archibald
Keyword(s):  
Neutron Stars ◽  
Millisecond Pulsar ◽  
Physical Processes ◽  
Recycling Process ◽  
Millisecond Pulsars ◽  
X Ray ◽  
System A ◽  
Multi Wavelength ◽  
Low Mass

AbstractTransitional millisecond pulsars (tMSPs), which are systems that harbor a pulsar in the throes of the recycling process, have emerged as a new source class since the discovery of the first such system a decade ago. These systems switch between accretion-powered low-mass X-ray binary (LMXB) and rotation-powered radio millisecond pulsar (RMSP) states, and provide exciting avenues to understand the physical processes that spin-up neutron stars to millisecond periods. During the last decade, three tMSPs, as well as a candidate source, have been extensively probed using systematic, multi-wavelength campaigns. Here we review the observational highlights from these campaigns and our general understanding of tMSPs.

scholarly journals Cosmological Evolution of the Central Engine in High-Luminosity, High-Accretion Rate AGN

2014 ◽  
Vol 1 (1) ◽  
pp. 90-95
Author(s):  
Matteo Guainazzi
Keyword(s):  
Active Galactic Nuclei ◽  
Accretion Rate ◽  
Galactic Nuclei ◽  
Seyfert Galaxies ◽  
Cosmological Evolution ◽  
High Luminosity ◽  
X Ray ◽  
Central Engine ◽  
The Status ◽  
Multi Wavelength

In this paper I discuss the status of observational studies aiming at probing the cosmological evolution of the central engine in high-luminosity, high-accretion rate Active Galactic Nuclei (AGN). X-ray spectroscopic surveys, supported by extensive multi-wavelength coverage, indicate a remarkable invariance of the accretion disk plus corona system, and of their coupling up to redshifts z≈6. Furthermore, hard X-ray (<em>E</em> &gt;10 keV) surveys show that nearby Seyfert Galaxies share the same central engine notwithstanding their optical classication. These results suggest that the high-luminosity, high accretion rate quasar phase of AGN evolution is homogeneous over cosmological times.

scholarly journals Multi-Wavelength Observations of EV Lacertae

2004 ◽  
Vol 219 ◽  
pp. 249-253
Author(s):  
Rachel A. Osten ◽  
Suzanne L. Hawley ◽  
Joel Allred ◽  
Christopher M. Johns-Krull ◽  
Christine Roark ◽  
...  
Keyword(s):  
Optical Observations ◽  
Electromagnetic Spectrum ◽  
Temperature Plasma ◽  
Optical Photometry ◽  
X Ray ◽  
Neupert Effect ◽  
Conflicting Evidence ◽  
Multi Wavelength ◽  
Flare Process ◽  
Ev Lac

We report on a large, multi-wavelength campaign to observe variability across the electromagnetic spectrum in the M dwarf flare star EV Lacertae, in 2001 September. The campaign involved X-ray (Chandra ACIS-S+HETG), UV (HST/STIS), and optical (McDonald) spectra, as well as optical photometry and multi-frequency radio (VLA) observations. EV Lac demonstrated both frequent and extreme variability during the course of the two day intensive recordings. Dispersed X-ray spectra confirm the metal underabundance seen in other active stars. The increase in continuum fluxes at short X-ray wavelengths during flare intervals compared to quiescent intervals signals the creation of high temperature plasma, a signature of the flare process. Multi-wavelength comparisons reveal interesting trends: X-ray flare frequencies are within the range predicted by optical observations, yet there is no correspondence between X-ray flares and optical flares in our data. Two UV flares occur during the rise stages of X-ray flares; a major radio flare is accompanied by a large optical flare, which has no apparent counterpart in the X-ray. The results give conflicting evidence for the applicability of the Neupert effect interpretation in stellar coronae.

A fast and portable microspectrophotometer for protein crystallography

1993 ◽  
Vol 26 (6) ◽  
pp. 839-842 ◽  
Author(s):  
A. Hadfield ◽  
J. Hajdu
Keyword(s):  
Structural Data ◽  
Array Detector ◽  
Time Resolved ◽  
X Ray ◽  
Additional Information ◽  
Near Ir ◽  
Photodiode Array Detector ◽  
Photodiode Array ◽  
The Right ◽  
Measurement Area

Spectroscopic measurements on crystals during X-ray data collection provide additional information on the composition of the crystal and can be used in the interpretation of structural data. This paper describes a portable microspectrophotometer to obtain UV–visible–near-IR spectra from single crystals during X-ray measurements. The instrument consists of a deuterium lamp, optical fibres, a pair of mirror lenses and a monochromator equipped with a photodiode array detector. Spectra can be recorded in short periods of time (a few milliseconds) from a measurement area of 0.10 mm diameter or smaller. The device can be used to monitor spectral changes in crystals during time-resolved X-ray experiments so that the X-ray camera can be triggered at the right moment as determined by the spectrum, thereby eliminating much of the present guesswork from such studies.

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