Subscribe to the gold package and get unlimited access to Shamra Academy
Register a new userHave we detected the most luminous ULX so far?
51
0
0.0
(
0
)
Authors
G. Miniutti
Ask ChatGPT about the research
No Arabic abstract
We report the XMM-Newton detection of a moderately bright X-ray source superimposed on the outer arms of the inactive spiral galaxy MCG-03-34-63 (z=0.0213). It is clearly offset from the nucleus (by about 19) but well within the D25 ellipse of the galaxy, just along its bar axis. The field has also been observed with the HST enabling us to compute a lower limit of > 94 on the X-ray to optical flux ratio which, together with the X-ray spectrum of the source, argues against a background AGN. On the other hand, the detection of excess X-ray absorption and the lack of a bright optical counterpart argue against foreground contamination. Short-timescale variability is observed, ruling out the hypothesis of a particularly powerful supernova. If it is associated with the apparent host galaxy, the source is the most powerful ULX detected so far with a peak luminosity of 1.35x10^41 erg/s in the 0.5-7 keV band. If confirmed by future multi-wavelength observations, the inferred bolometric luminosity (about 3x10^41 erg/s) requires a rather extreme beaming factor (larger than 115) to accommodate accretion onto a stellar-mass black hole of 20 solar masses and the source could represent instead one of the best intermediate-mass black hole candidate so far. If beaming is excluded, the Eddington limit implies a mass of >2300 solar masses for the accreting compact object.
rate research
Read More
The DNA molecule, apart from carrying the genetic information, plays a crucial role in a variety of biological processes and find applications in drug design, nanotechnology and nanoelectronics. The molecule undergoes significant structural transitions under the influence of forces due to physiological and non-physiological environments. Here, we summarize the insights gained from simulations and single-molecule experiments on the structural transitions and mechanics of DNA under force, as well as its elastic properties, in various environmental conditions, and discuss appealing future directions.
We report the first detection of flux variability in the most luminous X-ray source in the southern ring of the Cartwheel galaxy. XMM--Newton data show that the luminosity has varied over a timescale of six months from L[0.5-10] keV ~1.3 10^{41} erg/s, consistent with the previous Chandra observation, to L[0.5-10] keV < 6.4 x10^{40} erg/s. This fact provides the first evidence that the source is compact in nature and is not a collection of individual fainter sources, such as supernova remnants. The source has been repeatedly observed at the very high luminosity level of L[0.5-10] keV ~1.3 x 10^{41} erg/s, for a period of at least 4 years before dimming at the current level. It represents then the first example of an accreting object revealed in a long lived state of extremely high luminosity.
Identifying common patterns among events is a key ability in human and machine perception, as it underlies intelligent decision making. We propose an approach for learning semantic relational set abstractions on videos, inspired by human learning. We combine visual features with natural language supervision to generate high-level representations of similarities across a set of videos. This allows our model to perform cognitive tasks such as set abstraction (which general concept is in common among a set of videos?), set completion (which new video goes well with the set?), and odd one out detection (which video does not belong to the set?). Experiments on two video benchmarks, Kinetics and Multi-Moments in Time, show that robust and versatile representations emerge when learning to recognize commonalities among sets. We compare our model to several baseline algorithms and show that significant improvements result from explicitly learning relational abstractions with semantic supervision.
We report the high S/N observation on October 3, 2002 with XMM-Newton of the brightest X-ray flare detected so far from SgrA* with a duration shorter than one hour (~ 2.7 ks). The light curve is almost symmetrical with respect to the peak flare, and no significant difference between the soft and hard X-ray range is detected. The overall flare spectrum is well represented by an absorbed power-law with a soft photon spectral index of Gamma=2.5+/-0.3, and a peak 2-10 keV luminosity of 3.6 (+0.3-0.4) x 10^35 erg/s, i.e. a factor 160 higher than the Sgr A* quiescent value. No significant spectral change during the flare is observed. This X-ray flare is very different from other bright flares reported so far: it is much brighter and softer. The present accurate determination of the flare characteristics challenge the current interpretation of the physical processes occuring inside the very close environment of SgrA* by bringing very strong constraints for the theoretical flare models.
We present high resolution submillimeter interferometric imaging of two of the brightest high-redshift submillimeter galaxies known: GN20 and AzTEC1 at 0.8 and 0.3 arcsec resolution respectively. Our data - the highest resolution submillimeter imaging of high redshift sources accomplished to date - was collected in three different array configurations: compact, extended, and very extended. We derive angular sizes of 0.6 and 1.0 arcsec for GN20 and 0.3 and 0.4 arcsec for AzTEC1 from modeling their visibility functions as a Gaussian and elliptical disk respectively. Because both sources are B-band dropouts, they likely lie within a relatively narrow redshift window around z~4, which indicates their angular extent corresponds to physical scales of 4-8 and 1.5-3 kpc respectively for the starburst region. By way of a series of simple assumptions, we find preliminary evidence that these hyperluminous starbursts - with star formation rates >1000 $M_odot$ yr$^{-1}$ - are radiating at or close to their Eddington limit. Should future high resolution observations indicate that these two objects are typical of a population of high redshift Eddington-limited starbursts, this could have important consequences for models of star formation and feedback in extreme environments.
Log in to be able to interact and post comments
comments
Fetching comments
Sign in to be able to follow your search criteria
