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Synchronous X-ray/Optical QPOs from the Black Hole LMXB MAXI J1820+070 期刊论文 OAI收割
Monthly Notices of the Royal Astronomical Society, 2021
作者: HXMT

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black hole physics Low Mass X-ray Binaries accretion accretion discs stars: individual (MAXI J1820+070) Astrophysics - High Energy Astrophysical Phenomena Abstract: We present high-speed optical photometry from SAAO and SALT on the black hole LMXB MAXI J1820+070 (ASSASN-18ey), some of it simultaneous with NICER, Swift and Insight-HXMT X-ray coverage. We detect optical Quasi-Periodic Oscillations (QPOs) that move to higher frequencies as the outburst progresses, tracking both the frequency and evolution of similar X-ray QPOs previously reported. Correlated X-ray/optical data reveal a complex pattern of lags, including an anti-correlation and a sub-second lag that evolve over the first few weeks of outburst. They also show correlated components separated by a lag equal to the QPO period roughly centered on zero lag, implying that the inter-band variability is strongly and consistently affected by these QPOs at a constant phase lag of roughly ±Ю The synchronisation of X-ray and optical QPOs indicates that they must be produced in regions physically very close to each other we thus propose that they can be explained by a precessing jet model, based on analogies with V404 Cyg and MAXI J1348-630.

Periodicity Search on X-Ray Bursts of SGR J1935+2154 Using 8.5 yr of Fermi/GBM Data 期刊论文 OAI收割
The Astrophysical Journal, 2021, 卷号: 923, 页码: L30
作者: HXMT

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2008 1471 Astrophysics - High Energy Astrophysical Phenomena Abstract: We performed a systematic search for X-ray bursts of the SGR J1935+2154 using the Fermi Gamma-ray Burst Monitor continuous data dated from 2013 January to 2021 October. Eight bursting phases, which consist of a total of 353 individual bursts, are identified. We further analyze the periodic properties of our sample using the Lomb-Scargle periodogram. The result suggests that those bursts exhibit a period of ~238 days with a ~63.2% duty cycle. Based on our analysis, we further predict two upcoming active windows of the X-ray bursts. Since 2021 July, the beginning date of our first prediction has been confirmed by the ongoing X-ray activities of the SGR J1935+2154.

Divergence in the Aquilegia ecalcarata complex is correlated with geography and climate oscillations: Evidence from plastid genome data 期刊论文 OAI收割
MOLECULAR ECOLOGY, 2021, 卷号: 30, 期号: 22, 页码: 5796-5813
作者: Xue, Cheng; Geng, Fang-Dong; Li, Jiao-Jie; Zhang, Dan-Qing; Gao, Fei

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收藏 | 浏览/下载：20/0 | 提交时间：2023/02/24

Aquilegia ecalcarata climate oscillations floristic of eastern Asia phylogeographic plastid genome the Quaternary period

The relative controls of temperature and soil moisture on the start of carbon flux phenology and net ecosystem production in two alpine meadows on the Qinghai-Tibetan Plateau 期刊论文 OAI收割
JOURNAL OF PLANT ECOLOGY, 2020, 卷号: 13, 期号: 2, 页码: 247-255
作者: Chai, Xi; Shi, Peili; Song, Minghua; Zong, Ning; He, Yongtao

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收藏 | 浏览/下载：25/0 | 提交时间：2021/07/09

growing degree day growing season index the start of carbon uptake period net ecosystem production alpine meadows Qinghai-Tibet Plateau

The relative controls of temperature and soil moisture on the start of carbon flux phenology and net ecosystem production in two alpine meadows on the Qinghai-Tibetan Plateau 期刊论文 OAI收割
JOURNAL OF PLANT ECOLOGY, 2020, 卷号: 13, 期号: 2, 页码: 247-255
作者: Chai, Xi; Shi, Peili; Song, Minghua; Zong, Ning; He, Yongtao

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收藏 | 浏览/下载：23/0 | 提交时间：2021/07/09

growing degree day growing season index the start of carbon uptake period net ecosystem production alpine meadows Qinghai-Tibet Plateau

The relative controls of temperature and soil moisture on the start of carbon flux phenology and net ecosystem production in two alpine meadows on the Qinghai-Tibetan Plateau 期刊论文 OAI收割
JOURNAL OF PLANT ECOLOGY, 2020, 卷号: 13, 期号: 2
作者: Chai, Xi; Shi, Peili; Song, Minghua; Zong, Ning; He, Yongtao

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收藏 | 浏览/下载：20/0 | 提交时间：2020/11/25

growing degree day growing season index the start of carbon uptake period net ecosystem production alpine meadows Qinghai-Tibet Plateau

Geochronology, geochemistry and metallogenic dynamics of gold-polymetallic deposits in Xicha region, the northeastern margin of the North-China Platform 期刊论文 OAI收割
ACTA PETROLOGICA SINICA, 2020, 卷号: 36, 期号: 4, 页码: 1127-1150
作者: Qian Ye; Sun JinLei; Li YuJin; Yu Na; Liu JinLong

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收藏 | 浏览/下载：24/0 | 提交时间：2021/02/02

LIAO-JI BELT U-PB ZIRCON JILIN PROVINCE ISOTOPE SYSTEMATICS TECTONIC EVOLUTION JIAODONG PENINSULA CRUSTAL EVOLUTION YANSHAN PERIOD EASTERN BLOCK THRUST BELT Gold polymetallic Northeastern margin of the North-China Platform Liaoji Ocean the Paleo-Asian Ocean Subduction of the Paleo-Pacific plate Thinning of North China Craton Xicha region

Geochronology, geochemistry and metallogenic dynamics of gold-polymetallic deposits in Xicha region, the northeastern margin of the North-China Platform 期刊论文 OAI收割
ACTA PETROLOGICA SINICA, 2020, 卷号: 36, 期号: 4, 页码: 1127-1150
作者: Qian Ye; Sun JinLei; Li YuJin; Yu Na; Liu JinLong

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收藏 | 浏览/下载：14/0 | 提交时间：2021/02/02

LIAO-JI BELT U-PB ZIRCON JILIN PROVINCE ISOTOPE SYSTEMATICS TECTONIC EVOLUTION JIAODONG PENINSULA CRUSTAL EVOLUTION YANSHAN PERIOD EASTERN BLOCK THRUST BELT Gold polymetallic Northeastern margin of the North-China Platform Liaoji Ocean the Paleo-Asian Ocean Subduction of the Paleo-Pacific plate Thinning of North China Craton Xicha region

No pulsed radio emission during a bursting phase of a Galactic magnetar 期刊论文 OAI收割
Nature, 2020, 卷号: 587, 页码: 63-65
作者: HXMT

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收藏 | 浏览/下载：47/0 | 提交时间：2022/02/08

Astrophysics - High Energy Astrophysical Phenomena Abstract: Fast radio bursts (FRBs) are millisecond-duration radio transients of unknown physical origin observed at extragalactic distances^1-3. It has long been speculated that magnetars are the engine powering repeating bursts from FRB sources^4-13, but no convincing evidence has been collected so far¹⁴. Recently, the Galactic magnetar SRG 1935+2154 entered an active phase by emitting intense soft íray bursts¹⁵. One FRB-like event with two peaks (FRB 200428) and a luminosity slightly lower than the faintest extragalactic FRBs was detected from the source, in association with a soft íray/hard-X-ray flare^18-21. Here we report an eight-hour targeted radio observational campaign comprising four sessions and assisted by multi-wavelength (optical and hard-X-ray) data. During the third session, 29 soft-íray repeater (SGR) bursts were detected in íray energies. Throughout the observing period, we detected no single dispersed pulsed emission coincident with the arrivals of SGR bursts, but unfortunately we were not observing when the FRB was detected. The non-detection places a fluence upper limit that is eight orders of magnitude lower than the fluence of FRB 200428. Our results suggest that FRB-SGR burst associations are rare. FRBs may be highly relativistic and geometrically beamed, or FRB-like events associated with SGR bursts may have narrow spectra and characteristic frequencies outside the observed band. It is also possible that the physical conditions required to achieve coherent radiation in SGR bursts are difficult to satisfy, and that only under extreme conditions could an FRB be associated with an SGR burst.

An underlying clock in the extreme flip-flop state transitions of the black hole transient Swift J1658.2-4242 期刊论文 OAI收割
Astronomy and Astrophysics, 2020, 卷号: 641, 页码: A101
作者: HXMT

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收藏 | 浏览/下载：61/0 | 提交时间：2022/02/08

accretion accretion disks black hole physics X-rays: binaries time Astrophysics - High Energy Astrophysical Phenomena Abstract:
Aims: Flip-flops are top-hat-like X-ray flux variations, which have been observed in some transient accreting black hole binary systems, and feature simultaneous changes in the spectral hardness and the power density spectrum (PDS). They occur at a crucial time in the evolution of these systems, when the accretion disc emission starts to dominate over coronal emission. Flip-flops remain a poorly understood phenomenon, so we aim to thoroughly investigate them in a system featuring several such transitions.
Methods: Within the multitude of observations of Swift J1658.2-4242 during its outburst in early 2018, we detected 15 flip-flops, enabling a detailed analysis of their individual properties and the differences between them. We present observations by XMM-Newton, NuSTAR, Astrosat, Swift, Insight-HXMT, INTEGRAL, and ATCA. We analysed their light curves, searched for periodicities, computed their PDSs, and fitted their X-ray spectra, to investigate the source behaviour during flip-flop transitions and how the interval featuring flip-flops differs from the rest of the outburst.
Results: The flip-flops of Swift J1658.2-4242 are of an extreme variety, exhibiting flux differences of up to 77% within 100 s, which is much larger than what has been seen previously. We observed radical changes in the PDS simultaneous with the sharp flux variations, featuring transitions between the quasi-periodic oscillation types C and A, which have never been observed before. Changes in the PDS are delayed, but more rapid than changes in the light curve. Flip-flops occur in two intervals within the outburst, separated by about two weeks in which these phenomena were not seen. Transitions between the two flip-flop states occurred at random integer multiples of a fundamental period of 2.761 ks in the first interval and 2.61 ks in the second. Spectral analysis reveals the high and low flux flip-flop states to be very similar, but distinct from intervals lacking flip-flops. A change of the inner temperature of the accretion disc is responsible for most of the flux difference in the flip-flops. We also highlight the importance of correcting for the influence of the dust scattering halo on the X-ray spectra.