9 research outputs found
Current Status of Radio Source Databases
We review the history and present status of radio-source catalogue archiving
and on-line retrieval of radio source data. Large efforts were spent by the
first author in collecting and restoring electronic versions of new and old
source catalogues. Some 67 catalogues with ~520,000 entries were searchable via
the "Einstein On-line Service" (EOLS). When EOLS lost maintenance support in
1994 a group at SAO (Russia) started building software tools to search and
cross-identify objects between the major radio catalogues, maintained as the
"CATalog supporting System" (CATS) at the Special Astrophysical Observatory
(SAO, Russia). The independent efforts in east and west have recently been
joined. Almost 400 different source lists with ~2,000,000 entries have been
archived (and partly prepared) by us. All 5C and Penticton "P"-surveys and many
of the published WSRT survey lists are now available. CATS has been developed
by O. Verkhodanov, S. Trushkin, V. Chernenkov at SAO primarily to support
RATAN-600 radio observations. CATS runs under LINUX and can process requests on
the basis of various net protocols and via email. Almost 70 well-known radio
source catalogues and tables with about 1.3 Mrecords are now available via ftp
from CATS, as well as their documentation files. Twenty of the larger tables
may be searched simultaneously for objects in rectangular boxes of coordinates.
New routines for cross-matching are in progress. More and more catalogues are
being folded into CATS. CATS is supported by RFBR grant 96-07-89075.Comment: 2 pages, no figures; to appear in Proc. "Observational Cosmology with
the New Radio Surveys", eds. M. Bremer, N. Jackson & I. Perez-Fournon, Kluwer
Acad. Pres
The hypersoft state of Cygnus X-3 A key to jet quenching in X-ray binaries?
Context. Cygnus X-3 is a unique microquasar in the Galaxy hosting a Wolf-Rayet companion orbiting a compact object that most likely is a low-mass black hole. The unique source properties are likely due to the interaction of the compact object with the heavy stellar wind of the companion.Aims. In this paper, we concentrate on a very specific period of time prior to the massive outbursts observed from the source. During this period, Cygnus X-3 is in a so-called hypersoft state, in which the radio and hard X-ray fluxes are found to be at their lowest values (or non-detected), the soft X-ray flux is at its highest values, and sporadic gamma-ray emission is observed. We use multiwavelength observations to study the nature of the hypersoft state.Methods. We observed Cygnus X-3 during the hypersoft state with Swift and NuSTAR in X-rays and SMA, AMI-LA, and RATAN-600 in the radio. We also considered X-ray monitoring data from MAXI and gamma-ray monitoring data from AGILE and Fermi.Results. We found that the spectra and timing properties of the multiwavelength observations can be explained by a scenario in which the jet production is turned off or highly diminished in the hypersoft state and the missing jet pressure allows the wind to refill the region close to the black hole. The results provide proof of actual jet quenching in soft states of X-ray binaries
Strong low-frequency radio flaring from Cygnus X-3 observed with LOFAR
We present Low-Frequency Array (LOFAR) 143.5-MHz radio observations of
flaring activity during 2019 May from the X-ray binary Cygnus X-3. Similar to
radio observations of previous outbursts from Cygnus X-3, we find that this
source was significantly variable at low frequencies, reaching a maximum flux
density of about 5.8 Jy. We compare our LOFAR light curve with contemporaneous
observations taken at 1.25 and 2.3 GHz with the RATAN-600 telescope, and at 15
GHz with the Arcminute Microkelvin Imager (AMI) Large Array. The initial
143.5-MHz flux density level, 2 Jy, is suggested to be the delayed and
possibly blended emission from at least some of the flaring activity that had
been detected at higher frequencies before our LOFAR observations had begun.
There is also evidence of a delay of more than four days between a bright flare
that initially peaked on May 6 at 2.3 and 15 GHz, and the corresponding peak
( 5.8 Jy) at 143.5 MHz. From the multi-frequency light curves, we
estimate the minimum energy and magnetic field required to produce this flare
to be roughly 10 erg and 40 mG, respectively, corresponding to a minimum
mean power of 10 erg s. Additionally, we show that the
broadband radio spectrum evolved over the course of our observing campaign; in
particular, the two-point spectral index between 143.5 MHz and 1.25 GHz
transitioned from being optically thick to optically thin as the flare
simultaneously brightened at 143.5 MHz and faded at GHz frequencies
Discovery of X-Ray Polarization from the Black Hole Transient Swift J1727.8â1613
\ua9 2023. The Author(s). Published by the American Astronomical Society.We report the first detection of the X-ray polarization of the bright transient Swift J1727.8â1613 with the Imaging X-ray Polarimetry Explorer. The observation was performed at the beginning of the 2023 discovery outburst, when the source resided in the bright hard state. We find a time- and energy-averaged polarization degree of 4.1% \ub1 0.2% and a polarization angle of 2.\ub02 \ub1 1.\ub03 (errors at 68% confidence level; this translates to âŒ20Ï significance of the polarization detection). This finding suggests that the hot corona emitting the bulk of the detected X-rays is elongated, rather than spherical. The X-ray polarization angle is consistent with that found in submillimeter wavelengths. Since the submillimeter polarization was found to be aligned with the jet direction in other X-ray binaries, this indicates that the corona is elongated orthogonal to the jet
Search for very high-energy gamma-ray emission from the microquasar Cygnus X-1 with the MAGIC telescopes
The microquasar Cygnus X-1 displays the two typical soft and hard X-ray states of a black hole transient. During the latter, Cygnus X-1 shows a one-sided relativistic radio-jet. Recent detection of the system in the high energy (HE; E greater than or similar to 60 MeV) gamma-ray range with FermiLAT associates this emission with the outflow. Former MAGIC observations revealed a hint of flaring activity in the very high-energy (VHE; E greater than or similar to 100 GeV) regime during this X-ray state. We analyse similar to 97 h of Cygnus X-1 data taken with the MAGIC telescopes between July 2007 and October 2014. To shed light on the correlation between hard X-ray and VHE gamma rays as previously suggested, we study each main X-ray state separately. We perform an orbital phase-folded analysis to look for variability in the VHE band. Additionally, to place this variability behaviour in a multiwavelength context, we compare our results with Fermi-LAT, AGILE, Swift-BAT, MAXI, RXTE-ASM, AMI and RATAN-600 data. We do not detect Cygnus X-1 in the VHE regime. We establish upper limits for each X-ray state, assuming a power-law distribution with photon index Gamma = 3.2. For steady emission in the hard and soft X-ray states, we set integral upper limits at 95 per cent confidence level for energies above 200 GeV at 2.6 x 10(-12) photons cm(-2) s(-1) and 1.0 x 10(-11) photons cm(-2) s(-1), respectively. We rule out steady VHE gamma-ray emission above this energy range, at the level of theMAGIC sensitivity, originating in the interaction between the relativistic jet and the surrounding medium, while the emission above this flux level produced inside the binary still remains a valid possibility
Alfred Wegener-Institut fuer Polar- und Meeresforschung Bremerhaven Zweijahresbericht 1990/91
Available from TIB Hannover: ZO 6236(1990/91) / FIZ - Fachinformationszzentrum Karlsruhe / TIB - Technische InformationsbibliothekSIGLEDEGerman
Spectral, polarization and time-lag properties of GRS 1915+105 radio oscillations
We report high-sensitivity dual-frequency observations of radio oscillations from GRS 1915+ 105 following the decay of a major flare event in 2000 July. The oscillations are clearly observed at both frequencies, and the time-resolved spectral index traces the events between optically thin and thick states. While previously anticipated from sparse observations and simple theory, this is the first time a quasi-periodic signal has been seen in the radio spectrum, and is a clear demonstration that flat radio spectra can arise from the combination of emission from optically thick and thin regions. In addition, we measure the linear polarization of the oscillations, at both frequencies, at a level of about 1-2 per cent, with a flat spectrum. Cross-correlating the two light curves we find a mean delay, in the sense that the emission at 8640 MHz leads that at 4800 MHz, of around 600 s. Comparison with frequency-dependent time-delays reported in the literature reveals that this delay is variable between epochs. We briefly discuss possible origins for a varying time-delay, and suggest possible consequences