arXiv subjects

D. Varshalovich

Publications and source records attributed to D. Varshalovich.

7 recordsLinked to original sources

arXiv2010

Positron annihilation spectrum from the Galactic Centre region observed by SPI/INTEGRAL, revisited: annihilation in a cooling ISM?

We analyse SPI/INTEGRAL data on the 511 keV line from the Galactic Centre, accumulated over ~6 years of observations. We decompose the X-ray and soft gamma-ray emission of the central part of the Milky Way into a relatively compact "Bulge" and a more extended "Disk" components and report their spectral properties. The Bulge component shows a prominent 511 keV line and essentially no flux at 1.8 MeV, while the Disk component on the contrary contains a prominent 1.8 MeV line and a very weak annihilation line. We show that the spectral shape of the annihilation radiation (the narrow 511 keV line and the associated othro-positronium continuum) is surprisingly well described by a model of annihilation of hot positrons in a radiatively cooling interstellar medium (ISM). The model assumes that positrons are initially injected into a hot ($\sim 10^6$~K), volume filling ISM, which is allowed to freely cool via radiative losses. The annihilation time in such a medium is longer than the cooling time for temperatures higher than a few $10^{4}$~K. Thus, most of the positrons annihilate only after the gas has cooled down to $\sim 10^5$~K, giving rise to annihilation emission characteristic of a warm, ionized ISM.

astro-ph.HE↗

arXiv2005

A new constraint on the time dependence of the proton-to-electron mass ratio. Analysis of the Q 0347-383 and Q 0405-443 spectra

A new limit on the possible cosmological variation of the proton-to-electron mass ratio μ=m_p/m_e is estimated by measuring wavelengths of H_2 lines of Lyman and Werner bands from two absorption systems at z_abs = 2.5947 and 3.0249 in the spectra of quasars Q 0405-443 and Q 0347-383, respectively. Data are of the highest spectral resolution (R = 53000) and S/N ratio (30\div70) for this kind of study. We search for any correlation between z_i, the redshift of observed lines, determined using laboratory wavelengths as references, and K_i, the sensitivity coefficient of the lines to a change of μ, that could be interpreted as a variation of μover the corresponding cosmological time. We use two sets of laboratory wavelengths, the first one, Set (A) (Abgrall et al.), based on experimental determination of energy levels and the second one, Set (P) (Philip et al.), based on new laboratory measurements of some individual rest-wavelengths. We find Δμ/μ= (3.05+-0.75)10^-5 for Set (A), and Δμ/μ= (1.65+-0.74)10^-5 for Set (P). The second determination is the most stringent limit on the variation of μover the last 12 Gyrs ever obtained. The correlation found using Set (A) seems to show that some amount of systematic error is hidden in the determination of energy levels of the H$_2$ molecule.

astro-ph↗

arXiv2004

Positron annihilation spectrum from the Galactic Center region observed by SPI/INTEGRAL

The electron-positron annihilation spectrum observed by SPI/INTEGRAL during deep Galactic Center region exposure is reported. The line energy (510.954$\pm$0.075 keV) is consistent with the unshifted annihilation line. The width of the annihilation line is 2.37$\pm$0.25 keV (FWHM), while the strength of the ortho-positronium continuum suggests that the dominant fraction of positrons (94$\pm$6%) form positronium before annihilation. Compared to the previous missions these deep INTEGRAL observations provide the most stringent constraints on the line energy and width. Under the assumption of an annihilation in a single-phase medium these spectral parameters can be explained by a warm $T_e\sim 7000-4~10^4$ K gas with the degree of ionization larger than a few $10^{-2}$. One of the wide-spread ISM phases - warm ($T_e \sim 8000$ K) and weakly ionized (degree of ionization $\sim$ 0.1) medium satisfies these criteria. Other single-phase solutions are also formally allowed by the data (e.g. cold, but substantially ionized ISM), but such solutions are believed to be astrophysically unimportant. The observed spectrum can also be explained by the annihilation in a multi-phase ISM. The fraction of positrons annihilating in a very hot ($T_e \ge 10^6$ K) phase is constrained to be less than $\sim$8%. Neither a moderately hot ($T_e \ge 10^5$ K) ionized medium nor a very cold ($T_e \le 10^3$ K) neutral medium can make a dominant contribution to the observed annihilation spectrum. However, a combination of cold/neutral, warm/neutral and warm/ionized phases in comparable proportions could also be consistent with the data.

astro-ph↗

arXiv2004

A Hard X-ray survey of the Galactic Center with INTEGRAL/IBIS. Catalog of sources

During the period Aug.23-Sept.24 2003, the INTEGRAL observatory performed an ultra deep survey of the Galactic Center region with a record sensitivity at energies higher than 20 keV. We have analized images of the Galactic Center region obtained with the ISGRI detector of the IBIS telescope (15-200 keV) and present here a catalog of detected sources. In total, 60 sources with a flux higher than 1.5 mCrab have been detected. 44 of them were earlier identified as Galactic binary systems, 3 are extragalactic objects. 2 new sources are discovered.

astro-ph↗

arXiv2002

Does the proton-to-electron mass ratio vary in the course of cosmological evolution?

The possible cosmological variation of the proton-to-electron mass ratio was estimated by measuring the H_2 wavelengths in the high-resolution spectrum of the quasar Q~0347-382. Our analysis yielded an estimate for the possible deviation of μvalue in the past, 10 Gyr ago: for the unweighted value $Δμ/ μ= (3.0\pm2.4)\times10^{-5}$; for the weighted value \[ Δμ/ μ= (5.02\pm1.82)\times10^{-5}\] Since the significance of the both results does not exceed 3$σ$, further observations are needed to increase the statistical significance. In any case, this result may be considered as the most stringent estimate on an upper limit of a possible variation of μ(95% C.L.): \[ |Δμ/ μ| < 8\times 10^{-5} \] This value serves as an effective tool for selection of models determining a relation between possible cosmological deviations of the fine-structure constant αand the elementary particle masses (m$_p$, m$_e$, etc.).

astro-ph↗

arXiv2002

Do the Fundamental Constants Vary in the Course of the Cosmological Evolution?

We estimate the cosmological variation of the proton-to-electron mass ratio μ=m_p/m_e by measuring the wavelengths of molecular hydrogen transitions in the early universe. The analysis is performed using high spectral resolution observations (FWHM ~ 7 km/s) of two damped Lyman-αsystems at z_{abs}=2.3377 and 3.0249 observed along the lines of sight to the quasars Q 1232+082 and Q 0347-382 respectively. The most conservative result of the analysis is a possible variation of μover the last ~ 10 Gyrs, with an amplitude Δμ/μ= (5.7+-3.8)x10^{-5}. The result is significant at the 1.5σlevel only and should be confirmed by further observations. This is the most stringent estimate of a possible cosmological variation of μobtained up to now.

astro-ph↗

arXiv2001

HD Molecular Lines in an Absorption System at Redshift z = 2.3377

We have analyzed the spectrum of the quasar PKS 1232+082 obtained by Petitjean et al. (2000). HD molecular lines are identified in an absorption system at the redshift z=2.3377. The column density of HD molecules in the system is estimated, N(HD)=(1-4)x10^{14} cm^{-2}. The temperature of excitation of the first rotational level J=1 relative to the ground state J=0 is T_ex=70+-7 K. This is, to our knowledge, the first detection of HD molecules at high redshift.

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