ABSTRACT
We present the first sample of tidal disruption events (TDEs) discovered during the SRG all-sky survey. These 13 events were selected among X-ray transients detected in the 0° < l < 180° ...hemisphere by eROSITA during its second sky survey (2020 June 10 to December 14) and confirmed by optical follow-up observations. The most distant event occurred at z = 0.581. One TDE continued to brighten at least 6 months. The X-ray spectra are consistent with nearly critical accretion on to black holes of a few ×103 to $10^8\, \mathrm{ M}_\odot$, although supercritical accretion is possibly taking place. In two TDEs, a spectral hardening is observed 6 months after the discovery. Four TDEs showed an optical brightening apart from the X-ray outburst. The other nine TDEs demonstrate no optical activity. All 13 TDEs are optically faint, with Lg/LX < 0.3 (Lg and LX being the g band and 0.2–6 keV luminosity, respectively). We have constructed a TDE X-ray luminosity function, which can be fit by a power law with a slope of −0.6 ± 0.2, similar to the trend observed for optically selected TDEs. The total rate is estimated at (1.1 ± 0.5) × 10−5 TDEs per galaxy per year, an order of magnitude lower than inferred from optical studies. This suggests that X-ray bright events constitute a minority of TDEs, consistent with models predicting that X-rays can only be observed from directions close to the axis of a thick accretion disc formed from the stellar debris. Our TDE detection threshold can be lowered by a factor of ∼2, which should allow a detection of ∼700 TDEs by the end of the SRG survey.
Abstract
We report on observations of the Be/X-ray binary system Swift J1626.6–5156 performed with the Nuclear Spectroscopic Telescope ARray (NuSTAR) during a short outburst in 2021 March, following ...its detection by the MAXI monitor and Spektrum–Roentgen–Gamma (SRG) observatory. Our analysis of the broadband X-ray spectrum of the source confirms the presence of two absorption-like features at energies
E
∼ 9 and
E
∼ 17 keV. These had been previously reported in the literature and interpreted as the fundamental cyclotron resonance scattering feature (CRSF) and its first harmonic (based on Rossi X-ray Timing Explorer (RXTE) data). The better sensitivity and energy resolution of NuSTAR, combined with the low-energy coverage of Neutron star Interior Composition Explorer (NICER), allowed us to detect two additional absorption-like features at
E
∼ 4.9 keV and
E
∼ 13 keV. Therefore, we conclude that, in total, four cyclotron lines are observed in the spectrum of Swift J1626.6–5156: the fundamental CRSF at
E
∼ 4.9 keV and three higher spaced harmonics. This discovery makes Swift J1626.6–5156 the second accreting pulsar, after 4U 0115+63, whose spectrum is characterized by more than three lines of a cyclotronic origin, and implies that the source has the weakest confirmed magnetic field among all X-ray pulsars,
B
∼ 4 × 10
11
G. This discovery makes Swift J1626.6–5156 one of the prime targets for the upcoming X-ray polarimetry missions covering the soft X-ray band, such as Imaging X-ray Polarimetry Explorer (IXPE) and enhanced X-ray Timing and Polarimetry mission (eXTP).
ABSTRACT
We present a catalogue of point sources detected with the Mikhail Pavlinsky ART-XC telescope onboard the SRG observatory during a wide-field survey of the Galactic Bulge that was conducted ...as part of the mission’s calibration and performance verification phase in 2019. The survey consisted of nearly 18 d of consecutive scanning observations of the sky region |l| < 6 deg, |b| < 2.5 deg with the median sensitivity of 4 × 10−13 erg s−1 cm−2 in the 4–12 keV energy band, which allows the detection of sources down to a luminosity of 3 × 1033 erg s−1 near the Galactic Centre. Using a maximum-likelihood-based algorithm, 172 sources were detected. Of these, 153 are registered on the average 4–12 keV map and 18 sources are either extremely hard (detected only at energies above 7 keV) or highly variable (detected only in individual scans shorter than a day). For 121 sources, there are plausible counterparts in other X-ray source catalogues, including 43 with known classification. The remaining 51 sources are previously unknown objects, discovered by ART-XC during the Galactic Bulge survey.
ABSTRACT We report on the detection of type-C quasi-periodic oscillations during the initial stages of the outburst of Swift J1727.8–1613 in 2023. Using data of the INTEGRAL observatory along with ...the data of the Mikhail PavlinskyART-XC telescope on board Spektr-RG and X-ray Telescope (XRT) of the Neil Gehrels Swift observatory the fast growth of the quasi-periodic oscillations (QPO) frequency was traced. We present a hard X-ray light curve that covers the initial stages of the 2023 outburst – the fast rise and plateau – and demonstrate that the QPO frequency was stable during the plateau. The switching from type-C to type-B QPO was detected with the beginning of the source flaring activity. We have constructed a broad-band spectrum of Swift J1727.8−1613 and found an additional hard cutoff power-law spectral component extending at least up to 250 keV. Finally, we have obtained an upper limit on the hard X-ray flux at the beginning of the optical outburst and estimated the delay of the hard X-ray outburst with respect to the optical one.
We present an updated catalog of sources detected by the Mikhail Pavlinsky ART-XC telescope aboard the Spektrum-Roentgen-Gamma (SRG) observatory during its all-sky survey. It is based on the data of ...the first four and the partially completed fifth scans of the sky (ARTSS1-5). The catalog comprises 1545 sources detected in the 4–12 keV energy band. The achieved sensitivity ranges between ~4 × 10 −12 erg s −1 cm −2 near the ecliptic plane and ~7 × 10 −13 erg s −1 cm −2 near the ecliptic poles, which is a ~30–50% improvement over the previous version of the catalog based on the first two all-sky scans (ARTSS12). There are ~130 objects, excluding the expected contribution of spurious detections, that were not known as X-ray sources before the SRG/ART-XC all-sky survey. We provide information, partly based on our ongoing follow-up optical spectroscopy program, on the identification and classification of the majority of the ARTSS1-5 sources (1463), of which 173 are tentative at the moment. The majority of the classified objects (964) are extragalactic, a small fraction (30) are located in the Local Group of galaxies, and 469 are Galactic. The dominant classes of objects in the catalog are active galactic nuclei (911) and cataclysmic variables (192).
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ABSTRACT
We present the results of current observations of the young compact cluster of massive stars Westerlund 2 (Wd2) with the Mikhail Pavlinsky ART-XC telescope aboard the Spectrum-Roentgen-Gamma ...(SRG) observatory which we analysed together with the archival Chandra data. In general, Wd2 was detected over the whole electromagnetic spectrum including high-energy gamma rays, which revealed a cosmic ray acceleration in this object to the energies up to tens of TeV. The detection of Wd2 with ART-XC allowed us to perform a joint spectral analysis together with the high resolution Chandra observations of the diffuse emission from a few selected regions in the vicinity of the Wd2 core in the 0.4–20 keV range. To fit the Wd2 X-ray spectrum above a few keV one needs either a non-thermal power-law emission component, or a hot plasma with temperatures ∼ 5 keV. Our magnetohydrodynamic modelling of the plasma flows in Wd2 shows substantially lower electron temperatures in the system and thus the presence of the non-thermal component is certainly preferable. A kinetic model of the particle acceleration demonstrated that the non-thermal component may originate from the synchrotron radiation of multi-TeV electrons and positrons produced in Wd2 in accordance with the TeV photons detection from the source.
ABSTRACT
The Spectrum-Roentgen-Gamma (SRG) observatory is currently conducting its 4-yr all-sky X-ray survey, started on 2019 December 12. The survey is periodically interrupted for technological ...operations with the spacecraft. These time intervals are usually used by the Mikhail Pavlinsky ART-XC telescope to perform calibrations. In this context, SRG carried out scanning observations of the Puppis A supernova remnant (SNR) with the aim to check the imaging performance of ART-XC and to optimize the technique of image reconstruction for extended objects. Using the unique imaging capabilities of ART-XC and its uniform coverage of the entire Puppis A region, we attempted to investigate the morphology of this SNR at energies ≳ 4 keV, and to search for previously unknown X-ray sources. Puppis A was observed in 2019–2020, conducting 1.5° × 1.5° shallow surveys with an exposure of 36 h. Additional deep pointed observations of the central part of Puppis A were carried out in 2021 lasted 31 h to highlight the morphology of the extended emission. The X-ray emission of the Puppis A was significantly detected as an extended structure in the 4–6 keV energy band. The morphology of the emission is in general agreement with that observed in soft X-rays previously. The deep sky image of Puppis A obtained with the ART-XC telescope is characterized by a typical SNR shell rim morphology, an extended emission and a bright emission knot in the north-eastern part of the supernova shell. Also, four point X-ray sources have been detected, including three objects identified in catalogues, and one newly discovered X-ray emitter.
We present the results of our study of the X-ray pulsar IGR J21343+4738 based on NuSTAR, Swift, and SRG observations in the wide energy range 0.3–79 keV. The absence of absorption features in the ...energy spectra of the source, both averaged and phase-resolved ones, has allowed us to estimate the upper and lower limits on the magnetic field of the neutron star in the binary system,
and
G, respectively. Our spectral and timing analyses have shown that IGR J21343+4738 has all properties of a quasi-persistent X-ray pulsar with a pulsation period of
s and a luminosity
erg s
. Our analysis of the long-term variability of the object in X-rays has confirmed the possible orbital period of the binary system
days previously detected in the optical range.
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DOBA, EMUNI, FIS, FZAB, GEOZS, GIS, IJS, IMTLJ, IZUM, KILJ, KISLJ, MFDPS, NLZOH, NUK, OILJ, PILJ, PNG, SAZU, SBCE, SBJE, SBMB, SBNM, SIK, UILJ, UKNU, UL, UM, UPUK, VKSCE, ZAGLJ
Aims.
Fast radio bursts are bright radio transients whose origins are not yet understood. The search for a multi-wavelength counterpart of those events can set a tight constraint on the emission ...mechanism and the progenitor source.
Methods.
We conducted a multi-wavelength observational campaign on FRB 20180916B between October 2020 and August 2021 over eight activity cycles of the source. Observations were carried out in the radio band by the SRT both at 336 and 1547 MHz and the uGMRT at 400 MHz. Simultaneous observations were conducted by the optical telescopes Asiago (
Galileo
and
Copernico
), CMO SAI MSU, CAHA 2.2 m, RTT-150 and TNG, and X/
γ
-ray detectors on board the AGILE,
Insight–
HXMT, INTEGRAL, and
Swift
satellites.
Results.
We present the detection of 14 new radio bursts detected with the SRT at 336 MHz and seven new bursts with the uGMRT from this source. We provide the deepest prompt upper limits in the optical band for FRB 20180916B to date. In fact, the TNG/SiFAP2 observation simultaneous to a burst detection by uGMRT gives an upper limit
E
optical
/
E
radio
< 1.3 × 10
2
. Another burst detected by the SRT at 336 MHz was also co-observed by
Insight–
HXMT. The non-detection in the X-rays yields an upper limit (1 − 30 keV band) of
E
X − ray
/
E
radio
in the range of (0.9 − 1.3) × 10
7
, depending on the model that is considered for the X-ray emission.
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The magnetar SGR J1745–2900 located in the vicinity of the supermassive black hole Sgr A
was detected during its X-ray outburst with the Swift/XRT telescope in April 2013. For several months after ...its detection the source was observed with the NuSTAR observatory, which allowed pulsations with a period
s to be recorded. Using these observations, we have studied in detail the dependence of the pulse profile and the pulsed fraction on the energy and intensity of the magnetar. The pulsed fraction in the 3–5 and 5–10 keV energy bands is shown to be 40–50
, slightly increasing with decreasing flux. We have performed phase-resolved spectroscopy for the source in the energy range from 3 to
keV and show that the temperature of the emitting regions remains fairly stable during the pulse, while their apparent size changes significantly with phase.
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DOBA, EMUNI, FIS, FZAB, GEOZS, GIS, IJS, IMTLJ, IZUM, KILJ, KISLJ, MFDPS, NLZOH, NUK, OILJ, PILJ, PNG, SAZU, SBCE, SBJE, SBMB, SBNM, SIK, UILJ, UKNU, UL, UM, UPUK, VKSCE, ZAGLJ
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