arXiv subjects

C. Law

Publications and source records attributed to C. Law.

22 records · Page 2Linked to original sources

arXiv2002

Longitudinal Flow of Protons from 2-8 AGeV Central Au+Au Collisions

Rapidity distributions of protons from central $^{197}$Au + $^{197}$Au collisions measured by the E895 Collaboration in the energy range from 2 to 8 AGeV at the Brookhaven AGS are presented. Longitudinal flow parameters derived using a thermal model including collective longitudinal expansion are extracted from these distributions. The results show an approximately linear increase in the longitudinal flow velocity, $<βγ>_{L}$, as a function of the logarithm of beam energy.

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arXiv2002

The Origin of X-ray Emission from a Galactic Center Molecular Cloud: Low Energy Cosmic Ray Electrons

The Galactic center region near l$\approx0.2^0$ hosts a mixture of nonthermal linear filaments and thermal radio continuum features associated with the radio Arc. Chandra observations of this region reveal an X-ray filament and diffuse emission with an extent of roughly 60$''\times2''$ and 5$'\times3'$, respectively. The X-ray filament lies at the edge of the nonthermal radio filaments and a dense molecular shell G0.13-0.13 that has an unusually high kinetic temperature $\ge$70K. These observations demonstrate that the G0.13--0.13 molecular cloud and the nonthermal radio filaments of the Arc are interacting. The diffuse X-ray emission is correlated with the molecular shell and is fitted either by two-temperature (1 and 10 keV) thermal emission or by power-law and 1 keV thermal gas. Fluorescent 6.4 keV line emission is also detected throughout the molecular shell. This cloud coincides within the error circle of a steady unidentified EGRET source 3EGJ1746--2851. We argue that low-energy cosmic ray electrons (LECRe) produce the power-law continuum by bremsstrahlung and 6.4 keV line emission from the filament and the diffuse cloud with the implication on the origin of the Galactic ridge X-ray emission. The strong 6.4 keV Fe-line emission seen from other Galactic center clouds could be produced in a similar fashion rather than via fluorescent emission induced by a transient hard X-ray source in the Galactic center. In addition, heating by ionization induced by LECRe are also responsible for the high temperature of G0.13-0.13. The gamma-ray source is a result of brehmsstrahlung by the high-energy tail of the electron energy distribution.

astro-ph↗

arXiv2001

Detection of X-ray Emission from the Arches Cluster Near the Galactic Center

The Arches cluster is an extraordinarily compact massive star cluster with a core radius of about 10$''$ ($\sim$0.4 pc) and consisting of more than 150 O star candidates with initial stellar masses greater than 20~M$_\odot$ near G0.12-0.02. X-ray observations of the radio Arc near the Galactic center at l$\sim0.2^0$ which contains the Arches cluster have been carried out with the Advanced CCD Imaging Spectrometer (ACIS) on board Chandra X-ray Observatory. We report the detection of two X-ray sources from the Arches cluster embedded within a bath of diffuse X-ray emission extending beyond the edge of the cluster to at least 90$''\times60''$ (3.6 pc $\times$ 2.4 pc). The brightest component of the X-ray emission coincides with the core of the cluster and can be fitted with two-temperature thermal spectrum with a soft and hard component of 0.8 and 6.4 keV, respectively. The core of the cluster coincides with several ionized stellar wind sources that have previously been detected at radio wavelengths, suggesting that the X-ray emission from the core arises from stellar wind sources. The diffuse emission beyond the boundary of the cluster is discussed in the context of combined shocked stellar winds escaping from the cluster. We argue that the expelled gas from young clusters such as the Arches cluster may be responsible for the hot and extended X-ray emitting gas detected throughout the inner degree of the Galactic center.

astro-ph↗

arXiv2001

Laying the groundwork at the AGS: Recent results from experiment E895

The E895 Collaboration at the Brookhaven AGS has performed a systematic investigation of Au+Au collisions at 2-8 AGeV, using a large-acceptance Time Projection Chamber. In addition to extensive measurements of particle flow, spectra, two-particle interferometry, and strangeness production, we have performed novel hybrid analyses, including azimuthally-sensitive pion HBT, extraction of the six-dimensional pion phasespace density, and a first measurement of the Lambda-proton correlation function.

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