The mini-GWAC optical follow-up of gravitational wave alerts – results from the O2 campaign and prospects for the upcoming O3 run

The second(O2)observational campaign of gravitational waves(GWs)organized by the LIGO/Virgo Collaborations has led to several breakthroughs such as the detection of GW signals from merger systems involving black holes or neutrons stars.During O2,14 GW alerts were sent to the astronomical community with sky regions mostly covering over hundreds of square degrees.Among them,six were finally confirmed as real astrophysical events.Since 2013,a new set of ground-based robotic telescopes called Ground-based Wide Angle Camera system(GWAC)project and its pathfinder mini-GWAC has been developed to contribute to the various challenges of multi-messenger and time domain astronomy.The GWAC system is built up in the framework of the ground-segment system of the SVOM mission that will be devoted to the study of the multi-wavelength transient sky in the next decade.During O2,only the mini-GWAC telescope network was fully operational.Due to the wide field of view and fast automatic follow-up capabilities of the mini-GWAC telescopes,they were adept to efficiently cover the sky localization areas of GW event candidates.In this paper,we present the mini-GWAC pipeline we have set up to respond to GW alerts and we report our optical follow-up observations of eight GW alerts detected during the O2 run.Our observations provided the largest coverage of the GW localization areas with a short latency made by any optical facility.We found tens of optical transient candidates in our images,but none of those could be securely associated with any confirmed black hole-black hole merger event.Based on this first experience and the near future technical improvements of our network system,we will be more competitive in detecting the optical counterparts from some GW events that will be identified during the upcoming O3 run,especially those emerging from binary neutron star mergers.

Gravitationally lensed extended sources: the case of QSO RXJ0911

After a brief reminder of the mechanism of gravitational lensing of ex- tended sources, the particular case of the host galaxy of QSO RXJ0911, a high red-shift （z - 2.8） quadruply imaged quasar, is explored. The non linearity of the problem, together with the proximity of the source to a cusp of the lens inner caustic, has impor-tant consequences on the dependence of the image appearance on the size and shape of the source. Their expected main features and their interpretation in terms of source extension and shape are investigated in a spirit of simplicity and in preparation for the analysis of high sensitivity and spatial resolution images that will soon be within reach with the completion of the Atacama Large Millimeter/submillimeter Array （ALMA）. In particular, the information on source size carded by relative image brightness is dis-cussed. Extension of the results to other types of quadruply imaged quasars is briefly considered.

Vision and development in Trichoderma atroviride

Phototropism, the induction of carotenogenesis and reproductive structures, and resetting of the circadian rhythm are controlled by blue light. Trichoderma is used as a photomorphogenetic model due to its ability to conidiate upon exposure to light. In total darkness, T. atroviride grows indefinitely as a mycelium provided that nutrients are not limiting. However, nutrient deprivation and light trigger the conidiation process. A pulse of blue light given to a radially growing colony induces synchronous sporulation. A ring of conidiophores bearing green conidia is produced at what had been the colony perimeter at the time of the light pulse. All known responses to blue light in N. crassa are initiated by a couple of transcription factors encoded by the white-collar genes (wc -1 and wc-2). WC-1 and WC-2 bind to the promoters of light regulated genes to rapidly activate transcription in response to light. In T. atroviride the photolyase encoding gene phr1 undergoes fast transcriptional activation in response to light. The presence of putative WCC binding boxes in the promoter of phr1, suggested that light responses in Trichoderma could be under the control of white-collar homologues. We cloned two genes and demonstrated by gene replacement that both are essential for photoconidiation and photolyase gene expression. Therefore, they were named blue-light regulator one and two (blr1 and blr2). The BLR1 protein has all the characteristics of a blue-light photoreceptor. The generation of subtractive cDNA libraries allowed us to identify novel, BLR independent, light responses including the regulation of gene expression by blue-light. In addition, we recently initiated a Trichoderma ESTs sequencing project. Until now, we have sequenced above 3000 ESTs, from which we have obtained approximately 1800 unigenes. This unigene set was printed in microarrays and used to search for light induced genes. Twenty five clearly induced and around thirty repressed genes have been detected. Among this set we have found both blr dependent and independent blue light induced genes, strengthening our view of the existence of alternative light perception pathways. We also show the first evidence for the entry of Trichoderma into the conidiation process caused by mechanical injury, which remains unaltered in the mutants. Finally, an unprecedented crosstalk between light and glucose sensing was found involving the BLR1 and BLR2 proteins in the control of carbon deprivation induced conidiation.

An Earth-mass planet in a time of COVID-19:KMT-2020-BLG-0414Lb

We report the discovery of KMT-2020-BLG-0414 Lb,with a planet-to-host mass ratio q2=0.9-1.2×10-5=3-4 q⊕at 1σ,which is the lowest mass-ratio microlensing planet to date.Together with two other recent discoveries(4?q/q⊕?6),it fills out the previous empty sector at the bottom of the triangular(log s,log q)diagram,where s is the planet-host separation in units of the angular Einstein radiusθE.Hence,these discoveries call into question the existence,or at least the strength,of the break in the mass-ratio function that was previously suggested to account for the paucity of very low-q planets.Due to the extreme magnification of the event,Amax~1450 for the underlying single-lens event,its light curve revealed a second companion with q3~0.05 and|log s3|~1,i.e.,a factor~10 closer to or farther from the host in projection.The measurements of the microlens parallaxπE and the angular Einstein radiusθE allow estimates of the host,planet and second companion masses,(M1,M2,M3)~(0.3 M⊙,1.0 M⊕,17 MJ),the planet and second companion projected separations,(a⊥,2,a⊥,3)~(1.5,0.15 or 15)au,and system distance DL~1 kpc.The lens could account for most or all of the blended light(I~19.3)and so can be studied immediately with high-resolution photometric and spectroscopic observations that can further clarify the nature of the system.The planet was found as part of a new program of high-cadence follow-up observations of high-magnification events.The detection of this planet,despite the considerable difficulties imposed by COVID-19(two KMT sites and OGLE were shut down),illustrates the potential utility of this program.

MHD and kinetic analysis of flow bursts in the Earth's plasma sheet

In an attempt to study the flow bursts in the Earth’s plasma sheet we select an event that took place on August 7,2004 in the expansion phase of a substorm,using data from the geomagnetic index,solar wind data,plasma and magnetic field observations from C1 Cluster satellite(the Cluster mission has 4 satellites)and from Double Star TC-1 satellite.In MHD approach,TC-1 firstly observed the tailward flow,then the earthward,and finally the flow alternated in two directions.C1 firstly observed the earthward plasma flow,and then the tailward plasma flow.Before flow bursts are observed by TC-1 and C1,there are disturbances in local entropy with their tailward local entropy larger than those of the earthward.The kinetic features of the plasma flow observed by C1 are similar to those in MHD.However,kinetic characteristics of the plasma flow observed by TC-1 are far more than the description in MHD.The inadequacy mainly exists in two cases:(i)the firstly enhanced tailward flows given in MHD are found without significant increase of the energetic tailward flux;(ii)the almost stagnant flow in MHD is composed of the enhanced energetic ion flux in both earthward and tailward directions.The earthward flow burst observed by TC-1 might be multiple overshoots and rebounds.The earthward flow burst observed by C1 might be simply rebounded in the near-Earth.The pulsation observed by C1 is earlier than that observed by TC-1 with the former intensity less than that of the latter.After the energetic ion flux in the tailward direction is significantly enhanced,the power spectrum intensity of the ULF wave commences to increase obviously,which may suggest that the stream instability is closely correlated with ULF pulsations.

Nonadiabatic acceleration of plasma sheet ions related to ion cyclotron waves

The nonadiabatic acceleration of plasma sheet ions is important to the understanding of substorm energetic injections and the formation of ring current. Previous studies show that nonadiabatic acceleration of protons by magnetic field dipolarization is hard to occur at X>–10 RE because the time-scale of dipolarization(several minutes) is much larger than the gyroperiod of protons there(several seconds). In this paper, we present a case of nonadiabatic acceleration of plasma sheet ions observed by Cluster on October 30, 2006 at(XGSM, YGSM)=(-7.7, 4.7) RE. The nonadiabatic acceleration of ions is caused not by previously reported magnetospheric dipolarization but by the ultra low frequency(ULF) waves during magnetospheric dipolarization. The nonadiabatic acceleration of ions generates a new energy flux structure of ions, which is characterized by the usual energy flux increase of ions(28–80 ke V) and a concurrent energy flux decrease of ions in a lower energy range(10 e V–20 ke V). These new observations constitute a complete physical picture: The lower energy ions absorb the wave energy, and thus get accelerated to higher energy. We use a nonadiabatic model to interpret the ion energy flux variations. Both analytic and simulation results are in good agreement with the observations. This indicates that the nonadiabatic acceleration associated with ULF waves superposed on dipolarized magnetic field is an effective mechanism for ion energization in the near-Earth plasma sheet. The presented energy flux structures can be used as a proxy to identify the similar dynamic process.

Accretion in strong field gravity with eXTP

In this paper we describe the potential of the enhanced X-ray Timing and Polarimetry(eXTP) mission for studies related to accretion flows in the strong field gravity regime around both stellar-mass and supermassive black-holes. eXTP has the unique capability of using advanced "spectral-timing-polarimetry" techniques to analyze the rapid variations with three orthogonal diagnostics of the flow and its geometry, yielding unprecedented insight into the inner accreting regions, the effects of strong field gravity on the material within them and the powerful outflows which are driven by the accretion process.

Observatory science with eXTP

In this White Paper we present the potential of the enhanced X-ray Timing and Polarimetry(eXTP) mission for studies related to Observatory Science targets. These include flaring stars, supernova remnants, accreting white dwarfs, low and high mass X-ray binaries, radio quiet and radio loud active galactic nuclei, tidal disruption events, and gamma-ray bursts. eXTP will be excellently suited to study one common aspect of these objects: their often transient nature. Developed by an international Consortium led by the Institute of High Energy Physics of the Chinese Academy of Science, the eXTP mission is expected to be launched in the mid 2020s.