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New asynchronous polar discovered
Polars are close binaries consisting of an accreting magnetic white dwarf (hereinafter referred to as a WD) and a cool donor star (usually an M dwarf). The strong magnetic field of a WD (10-100 MG) makes these systems synchronous, i.e., leads to equality of the WD rotation period Pspin and the orbital period Porb. However, among the polars, there is a small group of asynchronous polars (8 systems with candidates are known) exhibiting asynchrony <3%. The nature of the asynchrony remains unclear, but it has been suggested that it may be due to the recent Nova explosion. Our work has supplemented the list of asynchronous polars with the system SDSS J085414.02+390537.3. We discovered its asynchrony from the analysis of ZTF photometry, in which different periods Porb and Pspin are distinguished as well as the beat period Pbeat (1/Pbeat = 1/Porb - 1/Pspin). The corresponding polar asynchrony is 0.3%. The system shows signs of a change in the main accreting pole, which are difficult to detect in previously known systems. The spectra of the polar obtained at the BTA telescope with the SCORPIO-1 and -2 instruments demonstrate Zeeman splitting of hydrogen lines and cyclotron harmonics, the modeling of which gives an estimate of the WD magnetic field B = 28-34 MG.
Authors:
Kolbin A. I., Suslikov M. V., Kochkina V. Yu., Borisov N. V., Burenkov A. N., Oparin D. V. (SAO RAS)
Published:
Kolbin A. I., Suslikov M. V.¸ Kochkina V. Yu., Borisov N. V., Burenkov A. N., Oparin, D. V. SDSS J085414.02+390537.3 – a new asynchronous polar, 2023, Astronomy Letters, Volume 49, Issue 8, p.475-485, DOI: 10.1134/S1063773723080029
Multi-frequency studies of the giant radio burst of the Black hole X-ray binary GRS1915+105 at time scale from 9 minutes to 9 days
In the multi-frequency (2-30 GHz) studies of an X-ray binary star with a black hole (BH), the prototype microquasar GRS 1915+105 with the RATAN-600 radio telescope, an extremely bright burst after the source transition to an extremely low and hard X-ray state was detected. The brightness of the burst reached 5.5 Jy at the frequency 2.3 GHz (that is, the radio luminosity increased up to 1035 erg/s) which is higher than the values received over 30 years from the date of discovery of the object. Then, for the first time, we traced the evolution of the flare at two frequencies 4.7 and 8.2 GHz in the new multi-azimuth (MA) observation mode of the telescope, when measurements were carried out every 8.6 minutes 31 times daily. The radio flare was accompanied by a gradual increase of the soft X-ray flux (MAXI, 2-20 keV). In the optically thin radio spectrum of the synchrotron electron radiation, the spectral index smoothly changed from +0.15 to -0.95 over the first eight days. The detected flux variations at times from 30 to 300 minutes correspond to the physical size of the radiation region from 4 to 40 astronomical units probably inside the jet emission. In eight MA measurements, for the first time quasi-periodic oscillations with an amplitude of up to 10% of the average flux were discovered on time intervals from 30 to 100 minutes. This giant flare in GRS1915+105 could be associated with formation of relativistic jet emission during the decreasing accretion, when, as has recently become known, a strong disk wind simultaneously obscures the main X-ray flux and reduces the rate of accretion. The obvious similarity of the burst event in GRS1915+105 with giant bursts in microquasars Cyg X-3, SS433, and Swift J1727.8-1613 implies similar physical processes of accretion onto black holes of stellar masses.
Over the 30-year history of studying the GRS1915+105, for the first time we have encountered an extremely unusual burst phenomenon in the X-ray binary system, that sheds light on the physics of accretion onto black holes of stellar masses and the formation of powerful collimated jets.
Authors:
Trushkin S.A., Bursov N.N., Shevchenko A.V., Tsybulev P.G., Nizhelsky N.A. (SAO RAS)
Published:
ATel #15974, #16008; #16168, HEA-2023
Discovery of the first candidate ultraluminous X-ray source with a neutron star with a field of 1012 G in a 1 billion-year-old star cluster
Analyzing data from the Chandra X-ray Observatory archive, we revealed signatures of an absorption line at ≈8 keV with a width-to-energy ratio of σ/E ≈ 0.2 in the spectrum of the ultraluminous X-ray source NGC5474 X-1 taken during an outburst, when the object's X-ray luminosity reached ≈2×1040 erg/s. It has been suggested that this broad line may be a cyclotron resonant scattering feature produced by transitions of electrons between Landau levels in magnetic field. This implies that the accretor in NGC5474 X-1must be a neutron star with a magnetic field of about 1012 G. The Hubble Space Telescope data shows that the X-ray outburst of the object was accompanied by more than 13 times increase of its U band flux. Optical observations of NGC5474 X-1 carried out in its faint state have allowed us to impose restrictions on the donor star mass (< 7 solar masses), as well as to reveal a star cluster of about 1 billion years old, the center of which is located at a projected distance of about 2 pc from the source. This cluster may be the parent cluster for NGC5474 X-1, but the presence of stars with an age of ~10 Myr within 300 pc around X-1 does not exclude an accidental projection of the ULX onto the old cluster.
Authors:
Vinokurov A.S., Sarkisyan A.N., Solovyeva Yu.N., Kostenkov A.E., Medvedev A.S., Fabrika S.N. in cooperation with Atapin K.E. (SAO RAS, SAI MSU)
Published:
K. Atapin, A. Vinokurov, A. Sarkisyan, Yu. Solovyeva, A. Kostenkov, A. Medvedev, S. Fabrika. NGC 5474 X-1: a neutron star ULX in an old stellar cluster?, Monthly Notices of the Royal Astronomical Society, 2023,Volume 527, Issue 4, pp.10185-10200, DOI: 10.1093/mnras/stad3719
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