V404 Cyg, Cyg X-3, V4641 Sgr, and GRS 1915+105 are among the brightest X-ray binaries and display complex behavior in their multiwavelength emission. Apart from Cyg X-3, the other three sources have large accretion disks, and there is evidence of a high orbital inclination. Therefore, any large scale geometrical change in the accretion disk can cause local obscuration events. On the other hand, Cyg X-3 orbits its Wolf-Rayet companion star inside the heavy stellar wind obscuring the X-ray source. We study here whether the peculiar X-ray spectra observed from all four sources can be explained by local obscuration events. We fit the source spectra with two physically motivated models describing either a scenario where all the intrinsic emission is reprocessed in the surrounding matter or where the emitter is surrounded by a thick torus with variable opening angle. We show that the X-ray spectra during specific times are similar in all four sources likely arising from the high-density environments where they are embedded. The fitted models suggest that a low-luminosity phase preceding an intense flaring episode in the 2015 outburst of V404 Cyg is heavily obscured, but intrinsically very bright (super-Eddington) accretion state. Similar spectral evolution to that of V404 Cyg is observed from the recent, unusually low-luminosity state of GRS 1915+105. The modeling results point to a geometry change in the (outflowing) obscuring matter in V404 Cyg and GRS 1915+105, which is also linked to the radio (jet) evolution. All sources display obscured X-ray emission but with different intrinsic luminosities which points towards different factors causing the obscuration. This work highlights the importance of taking into account the reprocessing of the X-ray emission in the surrounding medium in the modeling of the X-ray spectra that may well take place in other sources as well.
Detecting gamma-rays from microquasars is a challenging but worthwhile endeavor for understanding particle acceleration, the jet mechanism, and for constraining leptonic/hadronic emission models. We present results from a likelihood analysis on timescales of 1 d and 10 d of ~4 years worth of gamma-ray observations (0.1-10 GeV) by Fermi-LAT of Cyg X-1, Cyg X-3, GRS 1915+105, and GX 339-4. Our analysis reproduced all but one of the previous gamma-ray outbursts of Cyg X-3 as reported with Fermi or AGILE, plus 5 new days on which Cyg X-3 is detected at a significance of ~5-sigma that are not repor…
Microquasars, Galactic binary systems showing extended and variable radio emission, are potential gamma-ray emitters. Indications of gamma-ray transient episodes have been reported in at least two systems, Cyg X-1 and Cyg X-3. The identification of additional gamma-ray emitting microquasars is key for a better understanding of these systems. Very-high-energy gamma-ray emission from microquasars has been predicted to happen during periods of transient outbursts potentially connected with the formation of a jet-like outflow. Contemporaneous observations using the H.E.S.S. telescope array and the…
The outburst of V404 Cyg during the summer of 2015 reached unparalleled intensities at X-ray and soft gamma-ray energies with fluxes \( > 50\) Crab in the \(20-50\) keV energy band. To date, studies in the hard X-ray/soft gamma-ray energy domain have focused primarily on the energy spectra. In this work, timing analysis has been performed with \textit{INTEGRAL}/SPI data in the \(20-300\) keV energy range for \textit{INTEGRAL} revolution 1557, which corresponds to the brightest flare of V404 Cyg (on June, 26). The power spectra are fit with broken power-law and multi-Lorentzian models and compa…
Swift J1858.6-0814 was discovered by Swift-BAT on October 25, 2018. Here we report on the first follow-up NuSTAR observation of the source, which shows variability spanning two orders of magnitude in count rate on timescales of ~10-100 s. The power-spectrum of the source does not show any quasi-periodic oscillations or periodicity, but has a large fractional rms amplitude of 147%$\pm3$%, exhibiting a number of large flares throughout the observation. The hardness ratio (defined as $R_{10-79 \rm keV}/R_{3-10 \rm keV}$) of the flares tends to be soft, while the source spans a range of hardness r…
The Galactic black hole transient GRS1915+105 is famous for its markedly variable X-ray and radio behaviour, and for being the archetypal galactic source of relativistic jets. It entered an X-ray outburst in 1992 and has been active ever since. Since 2018 GRS1915+105 has declined into an extended low-flux X-ray plateau, occasionally interrupted by multi-wavelength flares. Here we report the radio and X-ray properties of GRS1915+105 collected in this new phase, and compare the recent data to historic observations. We find that while the X-ray emission remained unprecedentedly low for most of th…
We present optical spectroscopy obtained with the GTC, VLT and SALT telescopes during the decline of the 2016-2017 outburst of the black hole candidate GRS 1716-249 (Nova Oph 1993). Our 18-epoch data set spans 6 months and reveals that the observational properties of the main emission lines are very variable, even on time scales of a few hours. Several epochs are characterised by P-Cyg (as well as flat-top and asymmetric) profiles in the H$α$, H$β$ and He II ($λ$4686) emission lines, implying the presence of an accretion disc wind, which is likely hot and dense. The wind's terminal velocity ($…
We study the radio/X-ray correlation in Cyg X-3. It has been known that the soft and hard X-ray fluxes in the hard spectral state are correlated positively and negatively, respectively, with the radio flux. We show that this implies that the observed $\sim$1--100 keV flux (which is a fair approximation to the bolometric flux) is completely uncorrelated with the radio flux. We can recover a positive correlation (seen in other sources and expected theoretically) if the soft X-rays are strongly absorbed by a local medium. Then, however, the intrinsic X-ray spectrum of Cyg X-3 in its hard state be…
We report the detection of the state transitions and hysteresis effect in the two mini-outbursts of the black hole (BH) transient GRS 1739$-$278 following its 2014 major outburst. The X-ray spectral evolutions in these two mini-outbursts are similar to the major outburst, in spite of their peak luminosities and the outburst durations are one order of magnitude lower. We found the $L_\mathrm{hard-to-soft}$ and the $L_\mathrm{peak,soft}$ of the mini-outbursts also follow the correlation previous found in other X-ray binaries. The $L_\mathrm{hard-to-soft}$ of the mini-outbursts is still higher th…
The neutron star low-mass X-ray binary GRS 1741.9-2853 is a known type-I burster of the Galactic Center. It is transient, faint, and located in a very crowded region, only 10 arcmin from the supermassive black hole Sgr A*. Therefore, its bursting behavior has been poorly studied so far. In particular, its persistent emission has rarely been detected between consecutive bursts, due to lack of sensitivity or confusion. This is what made GRS 1741.9-2853 one of the nine "burst-only sources" identified by BeppoSAX a few years ago. The physical properties of GRS 1741.9-2853 bursts are yet of great i…
We show that the jet power $P_j$ and geometrically corrected $γ$-ray luminosity $L_γ$ for the X-ray binaries (XRBs) Cygnus X-1, Cygnus X-3, and V404 Cygni, and $γ$-ray upper limits for GRS 1915+105 and GX339-4, follow the universal scaling for the energetics of relativistic jets from black hole (BH) systems found by Nemmen et al. (2012) for blazars and GRBs. The observed peak $γ$-ray luminosity for XRBs is geometrically corrected; and the minimum jet power is estimated from the peak flux density of radio flares and the flare rise time. The $L_γ-P_j$ correlation holds across $\sim 17$ orders of…
Microquasars are potential $γ$-ray emitters. Indications of transient episodes of $γ$-ray emission were recently reported in at least two systems: Cyg X-1 and Cyg X-3. The identification of additional $γ$-ray-emitting microquasars is required to better understand how $γ$-ray emission can be produced in these systems. Theoretical models have predicted very high-energy (VHE) $γ$-ray emission from microquasars during periods of transient outburst. Observations reported herein were undertaken with the objective of observing a broadband flaring event in the $γ$-ray and X-ray bands. Contemporaneous …
We present a search for Galactic transient gamma-ray sources using 13 years of the Fermi Large Area Telescope data. The search is based on a recently developed variable-size sliding-time-window (VSSTW) analysis and aimed at studying variable gamma-ray emission from binary systems, including novae, gamma-ray binaries, and microquasars. Compared to the previous search for transient sources at random positions in the sky with 11.5 years of data, we included gamma rays with energies down to 500 MeV, increased a number of test positions, and extended the data set by adding data collected between Fe…
We present an optical spectroscopic study of the black hole X-ray transient V4641 Sgr (=SAX J1819.3-2525) covering the 1999, 2002 and 2004 outbursts. The spectra were taken over 22 different epochs during the low luminosity phases that follow the sharp and bright outburst peaks displayed by the system. The data reveal the frequent presence of wind-related features in H (Balmer) and He I emission lines in the form of P-Cygni profiles and strong emission lines with broad wings. The terminal velocity of the wind, as measured in the blue-shifted absorption (P-Cygni) components, is in the range of …
The 30-year recurrent symbiotic nova V3890 Sgr exploded 2019 August 28 and was observed with multiple X-ray telescopes. An XMM-Newton observation during the SSS phase captured a high degree of X-ray variability including a deep dip in the middle of the observation, an initial rise of similar depth and shape and, after the deep dip, smaller dips of 10% amplitude, which might be periodic over 18.1-minutes. An eclipse model of the dips yields clump sizes and orbital radii of 0.5-8 and 5-150 white dwarf radii, respectively. The simultaneous UV light curve shows no significant variations beyond slo…
Binary black holes as the recently detected sources of gravitational waves can be formed from massive stellar binaries in the field or by dynamical interactions in clusters of high stellar density, if the black holes are the remnants of massive stars that collapsed without natal kicks that would disrupt the binary system or eject the black holes from the cluster before binary black hole formation. Here are summarized and discussed the kinematics in three dimensions of space of five Galactic black hole X-ray binaries. For Cygnus X-1 and GRS 1915+105 it is found that the black holes of ~15 and ~…
A Multi-messenger Search for a Nearby Microquasar Contributor to the Cosmic Ray Knee
School of Physical Science and Technology, Southwest Jiaotong University（西南交通大学物理科学与技术学院）；State Key Laboratory of Particle Astrophysics, Institute of High Energy Physics, Chinese Academy of Sciences（中国科学院高能物理研究所粒子天体物理国家重点实验室）；University of Chinese Academy of Sciences（中国科学院大学）；TIANFU Cosmic Ray Research Center（天府宇宙线研究中心）
Microquasars, X-ray binaries displaying relativistic jets driven by accretion onto a compact object, are some of the most efficient accelerators in the Galaxy. Theoretical models predict Very High Energy (VHE) emission at the base of the jet where particles are accelerated to multi-TeV energies. This emission could be detected by present IACTs. %Moreover, gamma-ray fluxes should increase during flaring events when accretion rates are enhanced. The MAGIC telescope observed the microquasars GRS 1915+105, Cyg X-3, Cyg X-1 and SS433 for ~ 150 hours in total from 2005 to 2008. We triggered our obse…
We observed the X-ray binaries CirX-1, ScoX-1, GRS 1915+105, GX13+1, and CygX-1 with the Atacama Large Millimeter/submillimeter Array (ALMA). Unresolved continuum emission is found at the positions of all the sources at a frequency of 92 GHz, with flux densities ranging between 0.8 and 10 mJy/beam. In all cases the emission can be associated with jets that have been extensively observed at lower frequencies. We searched for line emission from H$α$ recombination, SiO,H2O, and CH3OH at the positions of all the sources and, for CirX-1 and CygX-1, also at regions where shocks associated with an in…
The NaI and BGO detectors on the Gamma-ray Burst Monitor (GBM) on Fermi are now being used for long-term monitoring of the hard X-ray/low energy gamma-ray sky. Using the Earth occultation technique as demonstrated previously by the BATSE instrument on the Compton Gamma-Ray Observatory, GBM can be used to produce multiband light curves and spectra for known sources and transient outbursts in the 8 keV to 1 MeV energy range with its NaI detectors and up to 40 MeV with its BGO detectors. Over 85% of the sky is viewed every orbit, and the precession of the Fermi orbit allows the entire sky to be v…
The NaI and BGO detectors on the Gamma ray Burst Monitor (GBM) on Fermi are now being used for long term monitoring of the hard X-ray/low energy gamma ray sky. Using the Earth occultation technique demonstrated previously by the BATSE instrument on the Compton Gamma Ray Observatory, GBM produces multiband light curves and spectra for known sources and transient outbursts in the 8 keV - 1 MeV band with its NaI detectors and up to 40 MeV with its BGO. Coverage of the entire sky is obtained every two orbits, with sensitivity exceeding that of BATSE at energies below ~25 keV and above ~1.5 MeV. We…
The broad energy range spanned by ASTRO-H instruments, from ~0.3 to 600 keV, with its high spectral resolution calorimeter and sensitive hard X-ray imaging, offers unique opportunities to study black holes and their environments. The ability to measure polarization is particularly novel, with potential sources including blazars, Galactic pulsars and X-ray binaries. In this White Paper, we present an overview of the synergistic instrumental capabilities and the improvements over prior missions. We also show how ASTRO-H fits into the multi-wavelength landscape. We present in more detail examples…
We report on the results from our search for the Wide-field Infrared Survey Explorer detection of the Galactic low-mass X-ray binaries. Among 187 binaries catalogued in Liu et al. (2007), we find 13 counterparts and two candidate counterparts. For the 13 counterparts, two (4U~0614+091 and GX~339$-$4) have already been confirmed by previous studies to have a jet and one (GRS~1915+105) to have a candidate circumbinary disk, from which the detected infrared emission arose. Having collected the broad-band optical and near-infrared data in literature and constructed flux density spectra for the oth…
The observed signatures of winds from X-ray binaries are broadly consistent with thermal winds, driven by X-ray irradiation of the outer accretion disc. Thermal winds produce mass outflow rates that can exceed the accretion rate in the disc. We study the impact of this mass loss on the stability and lightcurves of X-ray binaries subject to the thermal-viscous instability, which drives their outbursts. Strong mass loss could shut off outbursts early, as proposed for the 2015 outburst of V404 Cyg. We use an analytical model for thermal (Compton) wind mass loss. Scattering in the strong wind expe…
We present the discovery of an optical accretion disk wind in the X-ray transient Swift J1858.6-0814. Our 90-spectrum data set, taken with the 10.4m GTC telescope over 8 different epochs and across five months, reveals the presence of conspicuous P-Cyg profiles in He I at 5876 Angs and Halpha. These features are detected throughout the entire campaign, albeit their intensity and main observational properties are observed to vary on time-scales as short as five minutes. In particular, we observe significant variations in the wind velocity, between a few hundreds and ~ 2400 km/s. In agreement wi…
Recent work on jets and disk winds in low-mass X-ray binaries (LMXBs) suggests that they are to a large extent mutually exclusive, with jets observed in spectrally hard states and disk winds observed in spectrally soft states. In this paper we use existing literature on jets and disk winds in the luminous neutron star (NS) LMXB GX 13+1, in combination with archival Rossi X-ray Timing Explorer data, to show that this source is likely able to produce jets and disk winds simultaneously. We find that jets and disk winds occur in the same location on the source's track in its X-ray color-color diag…
In X-ray binaries, compact jets are known to commonly radiate at radio to infrared frequencies, whereas at optical to gamma-ray energies, the contribution of the jet is debated. The total luminosity, and hence power of the jet is critically dependent on the position of the break in its spectrum, between optically thick (self-absorbed) and optically thin synchrotron emission. This break, or turnover, has been reported in just one black hole X-ray binary (BHXB) thus far, GX 339-4, and inferred via spectral fitting in two others, A0620-00 and Cyg X-1. Here, we collect a wealth of multiwavelength …
We discovered a so called high-temperature blackbody (HBB) component, found in the 15 -- 40 keV range, in the broad-band X-ray energy spectra of black hole (BH) candidate sources. A detailed study of this spectral feature is presented using data from five of the Galactic BH binaries, Cyg X-1, GX 339-4, GRS 1915+105, SS 433 and V4641~Sgr in the low/hard, intermediate, high/soft and very soft spectral states (LHS, IS, HSS and VSS, respectively) and spectral transitions between them using {\it RXTE}, INTEGRAL and BeppoSAX data. In order to fit the broad-band energy spectra of these sources we use…
Gamma-ray emission at energies >100MeV has been detected from nine novae using the Fermi-LAT, and it can be explained by particle acceleration at shocks in these systems. Eight out of these nine objects are classical novae in which interaction of the ejecta with a tenuous circumbinary material is not expected to generate detectable gamma-ray emission. We examine whether particle acceleration at internal shocks can account for the gamma-ray emission from these novae. The shocks result from the interaction of a fast wind radiatively-driven by nuclear burning on the white dwarf with material ejec…
Polarimetry provides an avenue for probing the geometry and physical mechanisms producing optical radiation in many astrophysical objects, including stellar binary systems. We present the results of multiwavelength (BVR) polarimetric studies of a sample of historical black hole X-ray binaries, observed during their outbursts or in the quiescent (or near-quiescent) state. We surveyed both long- and short-period systems, located at different Galactic latitudes. We performed careful analysis of the interstellar polarization in the direction on the sources to reliably estimate the intrinsic source…
X-ray grating observations have revealed great detail in the spectra of Novae in the Super Soft Source (SSS) phase. Notable features in the SSS spectra are blue-shifted absorption lines, P-Cygni line profiles, and the absence of strong ionization edges, all of which are indicators of an expanding atmosphere. We present, and make publicly available, a set of 672 wind-type (WT) synthetic spectra, obtained from the expanding NLTE SSS models introduced in Van Rossum 2010 with the PHOENIX stellar atmosphere code. The set presented in this paper is limited to solar abundances with the aim to focus o…
X-ray grating spectra provide the confirmation of continued mass loss from novae in the super-soft source (SSS) phase of the outburst. In this work expanding nova atmosphere models are developed and used to study the effect of mass loss on the SSS spectra. The very high temperatures combined with high expansion velocities and large radial extension make nova in the SSS phase very interesting but also difficult objects to model. The radiation transport code PHOENIX was applied to SSS novae before, but careful analysis of the old results has revealed a number of problems which lead to new method…
