979 research outputs found
Excess gamma-rays in the direction of the rho Ophiuchi cloud: An exotic object?
The COS-B X-ray data in the direction of the rho Oph dark cloud show an extended structure; at the same time, the region of highest intensity has a spatial distribution compatible with a localized source; 2CG353+16 which is designated Oph gamma. The possibility of an excess gamma ray flux over what is expected on the basis of the interaction of average density cosmic rays with an estimated cloud mass of 2 to 4 000 M is still open, pending an extended CO survey matching the gamma ray data. Estimates for this excess factor are in the range 2 to 4. While the cloud mass may be underestimated, it should be noted that an excess of the same order appears to be present in the nearby Oph-Sag area, well surveyed in CO with the Columbia dish. Possible reasons for a gamma ray excess, in view of two recent observational developments: an Einstein X-ray survey and a VLA radio survey, both covering the approx 2 deg diameter Oph gamma error box. Current interpretations link the gamma ray excess to the cloud gas, in which some active agent is present: stellar winds, or interaction with the North Polar Spur
A Simultaneous Optical and X-ray Variability Study of the Orion Nebula Cluster. II. A Common Origin in Magnetic Activity
We present a statistical analysis of simultaneous optical and X-ray light
curves, spanning 600 ks, for 814 pre-main-sequence (PMS) stars in the Orion
Nebula Cluster. The aim of this study is to establish the relationship, if any,
between the sites of optical and X-ray variability, and thereby to elucidate
the origins of X-ray production in PMS stars. In a previous paper we showed
that optical and X-ray variability in PMS stars are very rarely
time-correlated. Here, using time-averaged variability indicators to examine
the joint occurrences of optical and X-ray variability, we confirm that the two
forms of variability are not directly causally related. However, a strong and
highly statistically significant correlation is found between optical
variability and X-ray luminosity. As this correlation is found to be
independent of accretion activity, we argue that X-ray production in PMS stars
must instead be intimately connected with the presence and strength of
optically variable, magnetically active surface regions (i.e. spots) on these
stars. Moreover, because X-ray variability and optical variability are rarely
time-correlated, we conclude that the sites of X-ray production are not
exclusively co-spatial with these regions. We argue that solar-analog coronae,
heated by topologically complex fields, can explain these findings.Comment: To appear in the Astrophysical Journal. 33 pages, 3 figure
X-ray inverse Compton emission from the radio halo of M87
A significant fraction of known galaxies contain an active galactic nucleus (AGN) at their cores, the site of violent activity and non-stellar radiation seen across the entire electromagnetic spectrum. This activity is thought to be due to the accretion of gas onto a massive black hole. A fraction of AGNs also eject collimated beams of energetic material, usually seen by virtue of its synchrotron emission in the radio band. Efforts to study these jets from AGNs in the X-ray band with the Einstein Observatory has led to several detections, most notably the jets in the nearby radio galaxies Centaurus A and Virgo A = M87. In their study of M87, Schreier, Gorenstein and Feigelson (1982) noted that, in addition to the synchrotron jet 10"-20" from the nucleus, X-rays appear to be generated in the diffuse radio halo 2'-5' from the nucleus. This finding may be particularly important as it may constitute the first known case of X-ray inverse Compton emission from AGN ejecta, allowing for the first time direct determination of the magnetic field strengths
Two component model for X-ray emission of radio selected QSO's
Using a large database of radio, optical, and x ray luminosities of AGNs with survival analysis, it was found that the x ray emission of the radio selected quasars has two components. One is related to the optical luminosity and the other is related to the radio luminosity
Parsec-scale X-ray Flows in High-mass Star-forming Regions
The Chandra X-ray Observatory is providing remarkable new views of massive
star-forming regions, revealing all stages in the life cycle of high-mass stars
and their effects on their surroundings. We present a Chandra tour of several
high-mass star-forming regions, highlighting physical processes that
characterize the life of a cluster of high-mass stars, from deeply-embedded
cores too young to have established an HII region to superbubbles so large that
they shape our views of galaxies. Along the way we see that X-ray observations
reveal hundreds of stellar sources powering great HII region complexes,
suffused by both hard and soft diffuse X-ray structures caused by fast O-star
winds thermalized in wind-wind collisions or by termination shocks against the
surrounding media. Finally, we examine the effects of the deaths of high-mass
stars that remained close to their birthplaces, exploding as supernovae within
the superbubbles that these clusters created. We present new X-ray results on
W51 IRS2E and 30 Doradus and we introduce new data on Trumpler 14 in Carina and
the W3 HII region complexes W3 Main and W3(OH).Comment: 6 pages, 3 figures, to appear in the proceedings of IAU Symposium
227,"Massive Star Birth - A Crossroads of Astrophysics," eds. R. Cesaroni, E.
Churchwell, M. Felli, and C.M. Walmsle
- …