Related papers: Quiescent and flaring X-ray emission from the near…

RX J1301.9+2747 is an ultrasoft active galactic nucleus (AGN) with unusual X-ray variability that is characterized by a long quiescent state and a short-lived flare state. The X-ray flares are found to recur quasi-periodically on a…

After more than a decade of actively accreting at about a tenth of the Eddington critical mass accretion rate, the neutron-star X-ray transient KS 1731-260 returned to quiescence in early 2001. We present a Chandra/ACIS-S observation taken…

The neutron star low-mass X-ray binary and intermittent millisecond X-ray pulsar HETE J1900.1-2455 returned to quiescence in late 2015, after a prolonged accretion outburst of ~10 yr. Using a Chandra observation taken ~180 d into quiescence…

After nearly a decade in quiescence, the accreting millisecond pulsar IGR J17511$-$3057 displayed a new outburst on 2025 February 11, its third since discovery, following previous activity in 2009 and 2015. We report on an XMM-Newton Target…

Recently, the Galactic magnetar SGR J1935+2154 has garnered attention due to its emission of an extremely luminous radio burst, reminiscent of Fast Radio Bursts (FRBs). SGR J1935+2154 is one of the most active magnetars, displaying flaring…

The XMM-Newton Extended Survey of the TMC (XEST) is a large program designed to systematically investigate the X-ray properties of young stellar/substellar objects in the TMC. In particular, the area surveyed by 15 XMM-Newton pointings (of…

Brown dwarfs are classified as objects which are not massive enough to sustain nuclear fusion of hydrogen, and are distinguished from planets by their ability to burn deuterium. Old (>10 Myr) brown dwarfs are expected to possess short-lived…

We report the discovery of several optical burst-like events from the low-mass X-ray binary MS1603.6+2600 (UW CrB). The events last for a few tens of seconds, exhibit a very fast rise and slow decay, and involve optical brightening of a…

We report here the results of a 90 ks BeppoSAX observation of the low mass X-ray binary and atoll source KS 1731-260 during a quiescent phase. From this observation we derive a source X-ray luminosity of \sim 10^{33} ergs/s (for a source…

We present Very Large Array observations of twelve late M and L dwarfs in the Solar neighborhood. The observed sources were chosen to cover a wide range of physical characteristics - spectral type, rotation, age, binarity, and X-ray and…

The characterization of exoplanets, their formation, evolution, and chemical changes is tightly linked to our knowledge of their host stars. In particular, stellar X-rays and UV emission have a strong impact on the dynamical and chemical…

Radio detections of ultracool dwarfs provide insight into their magnetic fields and the dynamos that maintain them, especially at the very bottom of the main sequence, where other activity indicators dramatically weaken. Until recently,…

Very Faint X-ray Transients (VFXTs) are a class of X-ray binary systems that exhibit occasional outbursts with peak X-ray luminosities (L_X< 1e36 erg s^-1) much lower than typical X-ray transients. On 22nd February 2024, during its daily…

We present high time-resolution multicolour optical observations of the quiescent X-ray transients GRS1124-684 (=GU Mus) and Cen X-4 (=V822 Cen) obtained with ULTRACAM. Superimposed on the secondary stars' ellipsoidal modulation in both…

We present a study of photometric flares on 154 low-mass ($\leq 0.2 \textrm{M}_{\odot}$) objects observed by the SPECULOOS-South Observatory from 1st June 2018 to 23rd March 2020. In this sample we identify 85 flaring objects, ranging in…

We report the results from archival XMM-Newton and INTEGRAL observations of the Supergiant Fast X-ray Transient (SFXT) IGR J18483-0311 in quiescence. The 18-60 keV hard X-ray behaviour of the source is presented here for the first time, it…

We report the discovery of an X-ray/UV stellar flare from the source LMC 335, captured by XMM-Newton in the field of the Large Magellanic Cloud. The flare event was recorded continuously in X-ray for its first 10 hours from the precursor to…

We report on BeppoSAX and Chandra observations of three Hard X-Ray Transients in quiescence containing fast spinning (P<5 s) neutron stars: A 0538-66, 4U 0115+63 and V 0332+53. These observations allowed us to study these transients at the…

SAX J1808.4-3658 is a unique source being the first Low Mass X-ray Binary showing coherent pulsations at a spin period comparable to that of millisecond radio pulsars. Here we present an XMM-Newton observation of SAX J1808.4-3658 in…

The Swift satellite monitored the quiescence of the low-mass X-ray binary transient Aql X-1 on a weekly basis during the March-November 2012 interval. A total of 42 observations were carried out in the soft X-ray (0.3-10 keV) band with the…