Editorial: Interplanetary medium variability as observed in the new era of spacecraft missions

Since 1970s an increasing number of heliospheric and planetary space missions have been launched as Helios (Porsche, 1981), Ulysses (Carvell, 1986), Wind (Acuña et al., 1995), ACE (Garrard et al., 1997), MAVEN (Jakosky and Maven Science Team, 2008), Rosetta (Wood, 1987), Cassini (Prange, 1985) collected a huge amount of data to characterize the interplanetary medium variability through the Heliosphere. Nowadays, the recently launched space missions BepiColombo (Benkhoff et al., 2021), Parker Solar Probe (Bale et al., 2016), and Solar Orbiter (Müller et al., 2020) provide more accurate in situ measurements through high-resolution instruments for monitoring the evolution of solar wind parameters at different heliocentric distances ranging from ∼0.05 A.U. to ∼10 A.U., and for providing new insights into the physics of various plasma processes related to the Sun and the interplanetary medium.</p

Swift monitoring of supergiant fast X-ray transients: The out-of-outburst behaviour and the flares from IGR J17544-2916 and XTE J1739-302

Supergiant Fast X-ray Transients (SFXTs) are a sub-class of High Mass X-ray Binaries (HMXBs) associated with OB supergiant companions and displaying transient X-ray activity. This behaviour is quite surprising since HMXBs hosting supergiants were known to be persistent sources, until the INTEGRAL discoveries obtained by means of the monitoring of the Galactic plane. We have been performing a monitoring campaign with Swift of four SFXTs with the main aim of characterizing both the long-term behaviour of these transients and the properties during bright outbursts. Here we discuss the properties of the X-ray emission observed outside the outbursts as well as the flares observed from two SFXTs: IGR J17544-2916 and XTE J1739-302. Contrarily to what previously thought, Swift allowed us to discover that SFXTs spend most of the time in accretion at a low level, even outside the bright outbursts, with an accretion luminosity of 1033-1034 erg s-1, and that the quiescent level ∼1032 erg s-1, is a much rarer state

The 100-month Swift catalogue of supergiant fast X-ray transients

Context. Supergiant fast X-ray transients (SFXTs) are high mass X-ray binaries (HMXBs) that are defined by their hard X-ray flaring behaviour. During these flares they reach peak luminosities of 1036–1037 erg s-1 for a few hours (in the hard X-ray), which are much shorter timescales than those characterizing Be/X-ray binaries. Aims. We investigate the characteristics of bright flares (detections in excess of 5σ) for a sample of SFXTs and their relation to the orbital phase. Methods. We have retrieved all Swift/BAT Transient Monitor light curves and collected all detections in excess of 5σ from both daily- and orbital-averaged light curves in the time range of 2005 February 12 to 2013 May 31 (MJD 53 413–56 443). We also considered all on-board detections as recorded in the same time span and selected those in excess of 5σ and within 4 arcmin of each source in our sample. Results. We present a catalogue of over a thousand BAT flares from 11 SFXTs, down to 15–150 keV fluxes of ~6 × 10-10 erg cm-2 s-1 (daily timescale) and ~1.5 × 10-9 erg cm-2 s-1 (orbital timescale, averaging ~800 s); the great majority of these flares are unpublished. The catalogue spans 100 months. This population is characterized by short (a few hundred seconds) and relatively bright (in excess of 100 mCrab, 15–50 keV) events. In the hard X-ray, these flares last generally much less than a day. Clustering of hard X-ray flares can be used to indirectly measure the length of an outburst, even when the low-level emission is not detected. We construct the distributions of flares, of their significance (in terms of σ), and of their flux as a function of orbital phase to infer the properties of these binary systems. In particular, we observe a trend of clustering of flares at some phases as Porb increases, which is consistent with a progression from tight circular or mildly eccentric orbits at short periods to wider and more eccentric orbits at longer orbital periods. Finally, we estimate the expected number of flares for a given source for our limiting flux and provide the recipe for calculating them for the limiting flux of future hard X-ray observatories

Swift observations of GRB 070110: An extraordinary X-ray afterglow powered by the central engine

We present a detailed analysis of Swift multiwavelength observations of GRB 070110 and its remarkable afterglow. The early X-ray light curve, interpreted as the tail of the prompt emission, displays a spectral evolution already seen in other gamma-ray bursts. The optical afterglow shows a shallow decay up to ~2 days after the burst, which is not consistent with standard afterglow models. The most intriguing feature is a very steep decay in the X-ray flux at ~2 × 10^4 s after the burst, ending an apparent plateau. The abrupt drop of the X-ray light curve rules out an external shock as the origin of the plateau in this burst and implies long-lasting activity of the central engine. The temporal and spectral properties of the plateau phase point toward a continuous central engine emission rather than the episodic emission of X-ray flares. We suggest that the observed X-ray plateau is powered by a spinning-down central engine, possibly a millisecond pulsar, which dissipates energy at an internal radius before depositing energy into the external shock

Swift observations of GRB 070110: An extraordinary X-ray afterglow powered by the central engine

We present a detailed analysis of Swift multiwavelength observations of GRB 070110 and its remarkable afterglow. The early X-ray light curve, interpreted as the tail of the prompt emission, displays a spectral evolution already seen in other gamma-ray bursts. The optical afterglow shows a shallow decay up to ~2 days after the burst, which is not consistent with standard afterglow models. The most intriguing feature is a very steep decay in the X-ray flux at ~2 × 10^4 s after the burst, ending an apparent plateau. The abrupt drop of the X-ray light curve rules out an external shock as the origin of the plateau in this burst and implies long-lasting activity of the central engine. The temporal and spectral properties of the plateau phase point toward a continuous central engine emission rather than the episodic emission of X-ray flares. We suggest that the observed X-ray plateau is powered by a spinning-down central engine, possibly a millisecond pulsar, which dissipates energy at an internal radius before depositing energy into the external shock

Swift and XMM-Newton observations of the extraordinary gamma-ray burst 060729: More than 125 days of x-ray afterglow

We report the results of the Swift andXMM-Newton observations of the Swift -discovered GRB 060729 (T90 = 115 s). The afterglow of this burst was exceptionally bright in X-rays as well as at UV/optical wavelengths, showing an unusually long slow decay phase ( Alpha = 0.14 +/- 0.02), suggesting a larger energy injection phase at early times than in other bursts. The X-ray light curve displays a break at about 60 ks after the burst. The X-ray decay slope after the break is Alpha = 1.29 +/- 0.03. Up to 125 days after the burst we do not detect a jet break, suggesting that the jet opening angle is larger than 28 degrees. We find that the X-ray spectra of the early phase change dramatically and can all be fitted by an absorbed singleYpower-law models or alternatively by a blackbody plus power-law model. The power-law fits show that the X-ray spectrum becomes steeper while the absorption column density decreases. In the blackbody model the temperature decreases from kT = 0.6 to 0.1 keV between 85 and 160 s after the burst in the rest frame. The afterglow was clearly detected up to 9 days after the burst in all six UVOT filters and in UVW1 even for 31 days. A break at about 50 ks is clearly detected in all six UVOT filters from a shallow decay slope of about 0.3 and a steeper decay slope of 1.3.The XMM-Newton observations started about 12 hr after the burst and show a typical afterglow X-ray spectrum with Beta[SUBSCRIPT x] = 1.1 and absorption column density of 1 x 10^21 cm^-

BepiColombo mission confirms stagnation region of Venus and reveals its large extent

The second Venus flyby of the BepiColombo mission offer a unique opportunity to make a complete tour of one of the few gas-dynamics dominated interaction regions between the supersonic solar wind and a Solar System object. The spacecraft pass through the full Venusian magnetosheath following the plasma streamlines, and cross the subsolar stagnation region during very stable solar wind conditions as observed upstream by the neighboring Solar Orbiter mission. These rare multipoint synergistic observations and stable conditions experimentally confirm what was previously predicted for the barely-explored stagnation region close to solar minimum. Here, we show that this region has a large extend, up to an altitude of 1900 km, and the estimated low energy transfer near the subsolar point confirm that the atmosphere of Venus, despite being non-magnetized and less conductive due to lower ultraviolet flux at solar minimum, is capable of withstanding the solar wind under low dynamic pressure

A short gamma-ray burst apparently associated with an elliptical galaxy at redshift z = 0.225.

Gamma-ray bursts (GRBs) come in two classes: long (> 2 s), soft-spectrum bursts and short, hard events. Most progress has been made on understanding the long GRBs, which are typically observed at high redshift (z approximately 1) and found in subluminous star-forming host galaxies. They are likely to be produced in core-collapse explosions of massive stars. In contrast, no short GRB had been accurately (< 10'') and rapidly (minutes) located. Here we report the detection of the X-ray afterglow from--and the localization of--the short burst GRB 050509B. Its position on the sky is near a luminous, non-star-forming elliptical galaxy at a redshift of 0.225, which is the location one would expect if the origin of this GRB is through the merger of neutron-star or black-hole binaries. The X-ray afterglow was weak and faded below the detection limit within a few hours; no optical afterglow was detected to stringent limits, explaining the past difficulty in localizing short GRBs