137,989 research outputs found
X-Ray Spectral Variability in Cygnus X-1
Spectral variability in different energy bands of X-rays from Cyg X-1 in
different states is studied with RXTE observations and time domain approaches.
In the hard tail of energy spectrum above keV, average peak aligned
shots are softer than the average steady emission and the hardness ratio
decreases when the flux increases during a shot for all states. In regard to a
soft band lower keV, the hardness in the soft state varies in an
opposite way: it peaks when the flux of the shot peaks. For the hard and
transition states, the hardness ratio in respect to a soft band during a shot
is in general lower than that of the steady component and a sharp rise is
observed at about the shot peak. For the soft state, the correlation
coefficient between the intensity and hardness ratio in the hard tail is
negative and decreases monotonically as the timescale increases from 0.01 s to
50 s, which is opposite to that in regard to a soft band. For the hard and
transition states, the correlation coefficients are in general negative and
have a trend of decrease with increasing timescale.Comment: 14 pages, 3 figures, accepted by Ap
Characterizing Some Gaia Alerts with LAMOST and SDSS
Gaia is regularly producing Alerts on objects where photometric variability
has been detected. The physical nature of these objects has often to be
determined with the complementary observations from ground-based facilities. We
have compared the list of Gaia Alerts (until 20181101) with archival LAMOST and
SDSS spectroscopic data. The date of the ground-based observation rarely
corresponds to the date of the Alert, but this allows at least the
identification of the source if it is persistent, or the host galaxy if the
object was only transient like a supernova. A list of Gaia Nuclear Transients
from Kostrzewa-Rutkowska et al. (2018) has been included in this search also.
We found 26 Gaia Alerts with spectra in LAMOST+SDSS labelled as stars (12 with
multi-epoch spectra). A majority of them are CVs. Similarly 206 Gaia Alerts
have associated spectra labelled as galaxies (49 with multi-epoch spectra).
Those spectra were generally obtained on a date different from the Alert date,
are mostly emission-line galaxies, leading to the suspicion that most of the
Alerts were due to a SN. As for the GNT list, we found 55 associated spectra
labelled as galaxies (13 with multi-epoch spectra). In two galaxies, Gaia17aal
and GNTJ170213+2543, was the date of the spectroscopic observation close enough
to the Alert date: we find a trace of the SN itself in their LAMOST spectrum,
both classified here as a type Ia SN. The GNT sample has a higher proportion of
AGNs, suggesting that some of the detected variations are also due to the AGN
itself. Similar for Quasars, we found 30 Gaia Alerts but 68 GNT cases have
single epoch quasar spectra, while 12 plus 23 have multi-epoch spectra. For ten
out of these 35, their multi-epoch spectra show appearance or disappearance of
the broad Balmer lines and also variations in the continuum, qualifying them as
"Changing Look Quasars".Comment: Accepted for publication in APSS, 14 pages, 8 figures, 2 table
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Research progress on coal mine laser methane sensor
This paper discusses the research progress of low-power technology of laser methane sensors for coal mine. On the basis of environment of coal mines, such as ultra-long-distance transmission and high stability, a series of studies have been carried out. The preliminary results have been achieved in the research of low power consumption, temperature and pressure compensation and reliability design. The technology is applied to various products in coal mines, and achieves high stability and high reliability in products such as laser methane sensor, laser methane detection alarm device, wireless laser methane detection alarm device, and optic fiber multichannel laser methane sensor. Experimental testing and analysis of the characteristics of laser methane sensors, combined with the actual application
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Fabrication of a high sensitive Ag-nanoparticle substrate and its application to the detection of toxic substances
Surface Enhanced Raman Scattering (SERS) is typically observed with the substrate in a liquid medium and it has been proposed as a promising technique for detecting low levels of pollutants in liquids. A technique is presented for self-assembly to immobilize Ag nanoparticles (Ag-NPs), with diameters ranging from 100 to 800nm on a solid support. Experimental results have been obtained through experiments using Ag-NPs active substrates to detect Rhodamine 6G (R6G) and crystal violet in the deionized water. Further, the SERS spectrum and Raman spectrum of phoxim were also measured, showing the enhancement in the performance of the active substrate as a result
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