Subscribe to the gold package and get unlimited access to Shamra Academy
Register a new userEXTraS discovery of a peculiar flaring X-ray source in the Galactic globular cluster NGC 6540
143
0
0.0
(
0
)
Ask ChatGPT about the research
No Arabic abstract
We report the discovery of a flaring X-ray source in the globular cluster NGC 6540, obtained during the EXTraS project devoted to a systematic search for variability in archival data of the XMM-Newton satellite. The source had a quiescent X-ray luminosity of the order of ~10^32 erg/s in the 0.5-10 keV range (for a distance of NGC 6540 of 4 kpc) and showed a flare lasting about 300 s. During the flare, the X-ray luminosity increased by more than a factor 40, with a total emitted energy of ~10^36 erg. These properties, as well as Hubble Space Telescope photometry of the possible optical counterparts, suggest the identification with a chromospherically active binary. However, the flare luminosity is significantly higher than what commonly observed in stellar flares of such a short duration, leaving open the possibility of other interpretations.
rate research
Read More
We report the discovery of a new ultraluminous X-ray source (ULX) associated with a globular cluster in the elliptical galaxy NGC 4649. The X-ray source was initially detected with a luminosity below 5 x 10^38 erg/s, but in subsequent observations 7 and 11 years later it had brightened substantially to 2 - 3 x 10^39 erg/s. Over the course of six separate observations it displayed significant spectral variability, in both continuum slope and absorption column. Short-term variability in the X-ray flux was also present in at least one observation. The properties of this object appear consistent with a stellar-mass black hole accreting at super-Eddington rates (i.e. in the ultraluminous accretion state), although a highly super-Eddington neutron star cannot be excluded. The coincidence of an increase in absorption column with a possible enhancement in short-term variability in at least one observation is suggestive of a clumpy radiatively-driven wind crossing our line-of-sight to the object
We report on the discovery of coherent pulsations at a period of 2.9 ms from the X-ray transient MAXI J0911-655 in the globular cluster NGC 2808. We observed X-ray pulsations at a frequency of $sim339.97$ Hz in three different observations of the source performed with XMM-Newton and NuSTAR during the source outburst. This newly discovered accreting millisecond pulsar is part of an ultra-compact binary system characterised by an orbital period of $44.3$ minutes and a projected semi-major axis of $sim17.6$ lt-ms. Based on the mass function we estimate a minimum companion mass of 0.024 M$_{odot}$, which assumes a neutron star mass of 1.4 M$_{odot}$ and a maximum inclination angle of $75^{circ}$ (derived from the lack of eclipses and dips in the light-curve of the source). We find that the companion stars Roche-Lobe could either be filled by a hot ($5times 10^{6}$ K) pure helium white dwarf with a 0.028 M$_{odot}$ mass (implying $isimeq58^{circ}$) or an old (>5 Gyr) brown dwarf with metallicity abundances between solar/sub-solar and mass ranging in the interval 0.065$-$0.085 M$_{odot}$ (16 < $i$ < 21). During the outburst the broad-band energy spectra are well described by a superposition of a weak black-body component (kT$sim$ 0.5 keV) and a hard cutoff power-law with photon index $Gamma sim$ 1.7 and cut-off at a temperature kT$_esim$ 130 keV. Up to the latest Swift-XRT observation performed on 2016 July 19 the source has been observed in outburst for almost 150 days, which makes MAXI J0911-655 the second accreting millisecond X-ray pulsar with outburst duration longer than 100 days.
We performed a search for eclipsing and dipping sources in the archive of the EXTraS project - a systematic characterization of the temporal behaviour of XMM-Newton point sources. We discovered dips in the X-ray light curve of 3XMM J004232.1+411314, which has been recently associated with the hard X-ray source dominating the emission of M31. A systematic analysis of XMM-Newton observations revealed 13 dips in 40 observations (total exposure time $sim$0.8 Ms). Among them, four observations show two dips, separated by $sim$4.01 hr. Dip depths and durations are variable. The dips occur only during low-luminosity states (L$_{0.2-12}<1times10^{38}$ erg s$^{-1}$), while the source reaches L$_{0.2-12}sim2.8times10^{38}$ erg s$^{-1}$. We propose this system to be a new dipping Low-Mass X-ray Binary in M31 seen at high inclination (60$^{circ}$-80$^{circ}$), the observed dipping periodicity is the orbital period of the system. A blue HST source within the Chandra error circle is the most likely optical counterpart of the accretion disk. The high luminosity of the system makes it the most luminous dipper known to date.
We report the discovery of the second accreting millisecond X-ray pulsar (AMXP) in the globular cluster NGC 6440. Pulsations with a frequency of 205.89 Hz were detected with the Rossi X-Ray Timing Explorer on August 30th, October 1st and October 28th, 2009, during the decays of ~4 day outbursts of a newly X-ray transient source in NGC 6440. By studying the Doppler shift of the pulsation frequency, we find that the system is an ultra-compact binary with an orbital period of 57.3 minutes and a projected semi-major axis of 6.22 light-milliseconds. Based on the mass function, we estimate a lower limit to the mass of the companion to be 0.0067 M_sun (assuming a 1.4 M_sun neutron star). This new pulsar shows the shortest outburst recurrence time among AMXPs (~1 month). If this behavior does not cease, this AMXP has the potential to be one of the best sources in which to study how the binary system and the neutron star spin evolve. Furthermore, the characteristics of this new source indicate that there might exist a population of AMXPs undergoing weak outbursts which are undetected by current all-sky X-ray monitors. NGC 6440 is the only globular cluster to host two known AMXPs, while no AMXPs have been detected in any other globular cluster.
We report and study the outburst of a new transient X-ray binary (XRB) in Terzan 5, the third detected in this globular cluster, Swift J174805.3-244637 or Terzan 5 X-3. We find clear spectral hardening in Swift/XRT data during the outburst rise to the hard state, thanks to our early coverage (starting at L_X ~ 4x10^{34} ergs/s) of the outburst. This hardening appears to be due to the decline in relative strength of a soft thermal component from the surface of the neutron star (NS) during the rise. We identify a {Type I X-ray burst} in Swift/XRT data with a long (16 s) decay time, indicative of {hydrogen burning on the surface of the} NS. We use Swift/BAT, Maxi/GSC, Chandra/ACIS, and Swift/XRT data to study the spectral changes during the outburst, identifying a clear hard-to-soft state transition. We use a Chandra/ACIS observation during outburst to identify the transients position. Seven archival Chandra/ACIS observations show evidence for variations in Terzan 5 X-3s non-thermal component, but not the thermal component, during quiescence. The inferred long-term time-averaged mass accretion rate, from the quiescent thermal luminosity, suggests that if this outburst is typical and only slow cooling processes are active in the neutron star core, such outbursts should recur every ~10 years.
Log in to be able to interact and post comments
comments
Fetching comments
Sign in to be able to follow your search criteria
