The impact of geomagnetically induced currents (GICs) on the power networks at middle and low latitudes has attracted attention in recent years with the increase of large-scale power networks. In this study, we report the GIC monitored at two low-latitude 500 kV substations of China during the large storm of 17 March 2015. The GIC due to the storm sudden commencement (SSC) was much higher than that during the storm main phase. This phenomenon is more likely to happen at low-latitude locations, highlighting the importance of SSC in inducing GIC in low-latitude power networks. Furthermore, we ran a global MHD model to simulate the GIC during this SSC event by using the solar wind observation as input. The model results reproduced the main features of the GIC. The study also indicated that the eastward component of the geoelectric field is dominant for low-latitude locations during the SSC events. Further, topology and electrical parameters of the power grids make significant differences in the GIC levels.

We present the Global Rapid Advanced Network Devoted to the Multi-messenger Addicts (GRANDMA). The network consists of 21 telescopes with both photometric and spectroscopic facilities. They are connected together thanks to a dedicated infrastructure. The network aims at coordinating the observations of large sky position estimates of transient events to enhance their follow-up and reduce the delay between the initial detection and the optical confirmation. The GRANDMA program mainly focuses on follow-up of gravitational-wave alerts to find and characterise the electromagnetic counterpart during the third observational campaign of the Advanced LIGO and Advanced Virgo detectors. But it allows for any follow-up of transient alerts involving neutrinos or gamma-ray bursts, even with poor spatial localisation. We present the different facilities, tools, and methods we developed for this network, and show its efficiency using observations of LIGO/Virgo S190425z, a binary neutron star merger candidate. We furthermore report on all GRANDMA follow-up observations performed during the first six months of the LIGO-Virgo observational campaign, and we derive constraints on the kilonova properties assuming that the events' locations were imaged by our telescopes.

We present extensive ultraviolet (UV) and optical photometry, as well as dense optical spectroscopy for type II Plateau (IIP) supernova SN 2016X that exploded in the nearby (∼ 15 Mpc) spiral galaxy UGC 08041. The observations span the period from 2 to 180 days after the explosion; in particular, the Swift UV data probably captured the signature of shock breakout associated with the explosion of SN 2016X. It shows very strong UV emission during the first week after explosion, with contribution of ∼ 20 -30% to the bolometric luminosity (versus 15% for normal SNe IIP). Moreover, we found that this supernova has an unusually long rise time of about 12.6 ± 0.5 days in the R band (versus ∼ 7.0 days for typical SNe IIP). The optical light curves and spectral evolution are quite similar to the fast-declining type IIP object SN 2013ej, except that SN 2016X has a relatively brighter tail. Based on the evolution of photospheric temperature as inferred from the Swif t data in the early phase, we derive that the progenitor of SN 2016X has a radius of about 930 ± 70 R ⊙ . This large-size star is expected to be a red supergiant star with an initial mass of 19 -20 M ⊙ based on the mass −− radius relation of the Galactic red supergiants, and it represents one of the most largest and massive progenitors found for SNe IIP.