Statistics of X-ray flares of Sagittarius A*: evidence for solar-like self-organized criticality phenomenon

X-ray flares have routinely been observed from the supermassive black hole, Sagittarius A$^\star$ (Sgr A$^\star$), at our Galactic center. The nature of these flares remains largely unclear, despite of many theoretical models. In this paper, we study the statistical properties of the Sgr A$^\star$ X-ray flares, by fitting the count rate (CR) distribution and the structure function (SF) of the light curve with a Markov Chain Monte Carlo (MCMC) method. With the 3 million second \textit{Chandra} observations accumulated in the Sgr A$^\star$ X-ray Visionary Project, we construct the theoretical light curves through Monte Carlo simulations. We find that the $2-8$ keV X-ray light curve can be decomposed into a quiescent component with a constant count rate of $\sim6\times10^{-3}~$count s$^{-1}$ and a flare component with a power-law fluence distribution $dN/dE\propto E^{-\alpha_{\rm E}}$ with $\alpha_{\rm E}=1.65\pm0.17$. The duration-fluence correlation can also be modelled as a power-law $T\propto E^{\alpha_{\rm ET}}$ with $\alpha_{\rm ET} < 0.55$ ($95\%$ confidence). These statistical properties are consistent with the theoretical prediction of the self-organized criticality (SOC) system with the spatial dimension $S = 3$. We suggest that the X-ray flares represent plasmoid ejections driven by magnetic reconnection (similar to solar flares) in the accretion flow onto the black hole.Comment: to appear in Ap

Bouncing Universe with Quintom Matter

The bouncing universe provides a possible solution to the Big Bang singularity problem. In this paper we study the bouncing solution in the universe dominated by the Quintom matter with an equation of state (EoS) crossing the cosmological constant boundary. We will show explicitly the analytical and numerical bouncing solutions in three types of models for the Quintom matter with an phenomenological EoS, the two scalar fields and a scalar field with a modified Born-Infeld action.Comment: 7 pages, 5 figure

Probing the Local Group Medium Toward Mkn 421 with Chandra and FUSE

We report the detection of highly-ionized gas at z~0 seen in resonant UV and X-ray absorption lines toward the z=0.03 blazar Mkn 421. A total of 13 X-ray and 3 UV lines were measured (or upper limits derived), including three lines in the OVII K-series and K\alpha transitions from neon, carbon, and nitrogen. From the three OVII lines we derive a 2\sigma Doppler parameter constraint of 24<b<55 km/s. The FUSE spectrum shows strong Galactic low--velocity OVI 1032A absorption as well as a possible weak OVI high-velocity component (HVC). The Doppler parameter of the low-velocity OVI measured with FUSE is ~3\sigma higher than that derived from the OVII line ratios, indicating that the OVII and Galactic OVI arise in different phases. This velocity dispersion, along with limits on the gas temperature and density from the X-ray line ratios (assuming a single phase with collisional ionization equilibrium plus photoionization) are all consistent with an extragalactic absorber. However, the OVII Doppler parameter is inconsistent with the high temperature required to produce the observed OVI_HVC/OVII ratio, implying that the HVC is probably not related to the OVII. In addition, the OVI_K\alpha line detected by Chandra implies a column density ~4 times higher than the 1032A absorption. Although an extragalactic absorber is fully consistent with the measured column density ratios, a Galactic origin cannot be ruled out given the uncertainties in the available data.Comment: 31 pages including 8 figures, 1 table. Figures 6-8 corrected and pertinent discussions updated. Accepted to ApJ, 10 September 2005 issu

White rice consumption and risk of esophageal cancer in Xinjiang Uyghur Autonomous Region, northwest China: a case-control study

This study investigated the association between white rice consumption and the risk of esophageal cancer in remote northwest China, where the cancer incidence is known to be high. A case-control study was conducted during 2008-2009 in Urumqi and Shihezi, Xinjiang Uyghur Autonomous Region of China. Participants were 359 incident esophageal cancer patients and 380 hospital-based controls. Information on habitual white rice consumption was obtained by personal interview using a validated semi-quantitative food frequency questionnaire. Logistic regression analyses were performed to assess the association between white rice consumption and the esophageal cancer risk. Confounding variables including socio-demographics, family history, dietary and lifestyle factors were adjusted in the multivariate model. The esophageal cancer patients reported lower consumption levels of white rice-based products, including cooked white rice and porridge, when compared to the control group. Overall, regular consumption of white rice foods was inversely associated with the esophageal cancer risk, the adjusted OR being 0.34 (95 % CI 0.23 to 0.52) for the highest (&gt;250 g) versus the lowest (&lt;92 g) tertile of daily intake. Similar reductions in risk were also apparent for high consumption levels of cooked white rice and porridge. In conclusion, habitual white rice consumption was associated with a reduced risk of esophageal cancer for adults residing in northwest China. Our findings provide evidence to support the continued consumption of white rice

AEGIS: Demographics of X-ray and Optically Selected AGNs

We develop a new diagnostic method to classify galaxies into AGN hosts, star-forming galaxies, and absorption-dominated galaxies by combining the [O III]/Hbeta ratio with rest-frame U-B color. This can be used to robustly select AGNs in galaxy samples at intermediate redshifts (z<1). We compare the result of this optical AGN selection with X-ray selection using a sample of 3150 galaxies with 0.3<z<0.8 and I_AB<22, selected from the DEEP2 Galaxy Redshift Survey and the All-wavelength Extended Groth Strip International Survey (AEGIS). Among the 146 X-ray sources in this sample, 58% are classified optically as emission-line AGNs, the rest as star-forming galaxies or absorption-dominated galaxies. The latter are also known as "X-ray bright, optically normal galaxies" (XBONGs). Analysis of the relationship between optical emission lines and X-ray properties shows that the completeness of optical AGN selection suffers from dependence on the star formation rate and the quality of observed spectra. It also shows that XBONGs do not appear to be a physically distinct population from other X-ray detected, emission-line AGNs. On the other hand, X-ray AGN selection also has strong bias. About 2/3 of all emission-line AGNs at L_bol>10^44 erg/s in our sample are not detected in our 200 ks Chandra images, most likely due to moderate or heavy absorption by gas near the AGN. The 2--7 keV detection rate of Seyfert 2s at z~0.6 suggests that their column density distribution and Compton-thick fraction are similar to that of local Seyferts. Multiple sample selection techniques are needed to obtain as complete a sample as possible.Comment: 24 pages, 14 figures, submitted to ApJ. Version 2 matches the ApJ accepted version. Sec 3 was reorganized and partly rewritten with one additional figure (Fig.3

eDIG-CHANGES I: extended Hα emission from the extraplanar diffuse ionized gas (eDIG) around CHANG-ES galaxies

The extraplanar diffuse ionized gas (eDIG) represents the cool/warm ionized gas reservoir around galaxies. We present spatial analysis of the Hα images of 22 nearby edge-on spiral galaxies taken with the Apache Point Observatory 3.5-m telescope (eDIG-CHANGES). We conduct an exponential fit to the vertical Hα intensity profiles of the galaxies, of which 16 can be decomposed into thin + thick disk components. The median value of the Hα scale height of the thick disk is ⟨hHα⟩=1.13±0.14 kpc ⁠. We further examine the dependence of hHα on the stellar mass, SFR, and SFR surface density (SFRSD) of the galaxies. We find a tight sublinear correlation between hHα and SFR, expressed in hHα ∝ SFRα, where α ≈ 0.29. Moreover, the offset of individual galaxies from the best-fit SFR-hHα relation, expressed in hHα/SFRα, shows significant anti-correlation with SFRSD. We further compare the vertical extension of the eDIG to multi-wavelength measurements of other CGM phases. We find the eDIG slightly more extended than the neutral gas. This indicates the existence of some extended ionizing sources, in addition to the leaking photons from the disk star formation regions. Most galaxies have an X-ray scale height smaller than Hα, suggesting the majority of the X-ray photons are actually from the thick disk instead of the extended CGM. hHα is comparable to the L-band radio continuum scale height. This indicates that the thermal and non-thermal electrons have similar spatial distributions, a natural result if both are transported outwards by a galactic wind. This further indicates the thermal gas, cosmic rays, and magnetic field may be close to energy equipartition. © 2023 The Author(s) Published by Oxford University Press on behalf of Royal Astronomical Society.This work is supported by the National Key R&D Program of China (grant No. 2017YFA0402600), and NSFC (grant Nos. 11890692 and 12133008). We acknowledge the science research grants from the China Manned Space Project with No. CMS-CSST-2021-A04. HL is supported by NASA through the NASA Hubble Fellowship grant HST-HF2-51438.001-A awarded by the Space Telescope Science Institute, which is operated by the Association of Universities for Research in Astronomy, Incorporated, under NASA contract NAS5-26555. RJD acknowledges support by Deutsche Forschungsgemeinschaft Sonderforschungsbereich 1491. TW acknowledges financial support (grant No. SEV-2017-0709) funded by MCIN/AEI/ 10.13039/501100011033, from the coordination of the participation in SKA-SPAIN, funded by the Ministry of Science and Innovation (MCIN).With funding from the Spanish government through the "Severo Ochoa Centre of Excellence" accreditation (CEX2021-001131-S).Peer reviewe

Multiple Organ System Defects and Transcriptional Dysregulation in the Nipbl+/− Mouse, a Model of Cornelia de Lange Syndrome

Cornelia de Lange Syndrome (CdLS) is a multi-organ system birth defects disorder linked, in at least half of cases, to heterozygous mutations in the NIPBL gene. In animals and fungi, orthologs of NIPBL regulate cohesin, a complex of proteins that is essential for chromosome cohesion and is also implicated in DNA repair and transcriptional regulation. Mice heterozygous for a gene-trap mutation in Nipbl were produced and exhibited defects characteristic of CdLS, including small size, craniofacial anomalies, microbrachycephaly, heart defects, hearing abnormalities, delayed bone maturation, reduced body fat, behavioral disturbances, and high mortality (75–80%) during the first weeks of life. These phenotypes arose despite a decrease in Nipbl transcript levels of only ∼30%, implying extreme sensitivity of development to small changes in Nipbl activity. Gene expression profiling demonstrated that Nipbl deficiency leads to modest but significant transcriptional dysregulation of many genes. Expression changes at the protocadherin beta (Pcdhb) locus, as well as at other loci, support the view that NIPBL influences long-range chromosomal regulatory interactions. In addition, evidence is presented that reduced expression of genes involved in adipogenic differentiation may underlie the low amounts of body fat observed both in Nipbl+/− mice and in individuals with CdLS