THE X-RAY FLARING PROPERTIES OF Sgr A* DURING SIX YEARS OF MONITORING WITH<i>SWIFT</i>

Degenaar, N.; Miller, J. M.; Kennea, J. A.; Gehrels, N.; Reynolds, M. T.; Wijnands, Rudy

doi:10.1088/0004-637x/769/2/155

Cited by 65 publications

(138 citation statements)

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“…Using the data, Neilsen et al (2013, hereafter N13) detect 39 flares. Flares have also been detected in observations made with other X-ray observatories such as XMM-Newton (Porquet et al 2003;Bélanger et al 2005;Porquet et al 2008), Swift (Degenaar et al 2013), and NuS-TAR (Barrière et al 2014). The suggested radiation mechanisms of X-ray flares include synchrotron (Yuan, Quataert & Narayan 2003, 2004Dodds-Eden et al 2009), inverse Compton scattering (Markoff et al 2001;Yuan, Quataert & Narayan 2003;Eckart et al 2004Eckart et al , 2006aLiu, Melia & Petrosian 2006), and bremsstrahlung (Liu & Melia 2002).…”

Section: Introductionmentioning

confidence: 94%

A systematicChandrastudy of Sgr A^⋆– I. X-ray flare detection

Yuan¹,

Wang²

2015

Mon. Not. R. Astron. Soc.

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Daily X-ray flaring represents an enigmatic phenomenon of Sgr A ⋆ -the supermassive black hole at the center of our Galaxy. We report initial results from a systematic X-ray study of this phenomenon, based on extensive Chandra observations obtained from 1999 to 2012, totaling about 4.5 Ms. We detect flares, using a combination of the maximum likelihood and Markov Chain Monte Carlo methods, which allow for a direct accounting for the pile-up effect in the modeling of the flare lightcurves and an optimal use of the data, as well as the measurements of flare parameters, including their uncertainties. A total of 82 flares are detected. About one third of them are relatively faint, which were not detected previously. The observation-toobservation variation of the quiescent emission has an average root-mean-square of 6% − 14%, including the Poisson statistical fluctuation of faint flares below our detection limits. We find no significant long-term variation in the quiescent emission and the flare rate over the 14 years. In particular, we see no evidence of changing quiescent emission and flare rate around the pericenter passage of the S2 star around 2002. We show clear evidence of a shortterm clustering for the ACIS-S/HETG 0th-order flares on time scale of 20 − 70 ks. We further conduct detailed simulations to characterize the detection incompleteness and bias, which is critical to a comprehensive follow-up statistical analysis of flare properties. These studies together will help to establish Sgr A ⋆ as a unique laboratory to understand the astrophysics of prevailing low-luminosity black holes in the Universe.

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Section: Introductionmentioning

confidence: 94%

A systematicChandrastudy of Sgr A^⋆– I. X-ray flare detection

Yuan¹,

Wang²

2015

Mon. Not. R. Astron. Soc.

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“…Our choice to monitor the central square degree of our Galaxy was motivated by the fact that this region is populated by nearly 20 known X-ray transients, several of which undergo sub-luminous accretion episodes (Muno et al 2005a;Wijnands et al 2006a;Kennea et al 2006;Degenaar & Wijnands 2009;Degenaar et al 2011b). The relatively wide field of view (FOV; ∼30 × 30 ) and large collecting area (∼1100 cm 2 at 1 keV) of XMM-Newton make it an excellent facility for surveying sky regions down to relatively faint flux levels.…”

Section: Observationsmentioning

confidence: 99%

A four-yearXMM-Newton/Chandramonitoring campaign of the Galactic centre: analysing the X-ray transients

Degenaar

Wijnands

Cackett

et al. 2012

A&A

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We report on the results of a four-year long X-ray monitoring campaign of the central 1.2 square degrees of our Galaxy, performed with Chandra and XMM-Newton between 2005 and 2008. Our study focuses on the properties of transient X-ray sources that reach 2-10 keV luminosities of L X 10 34 erg s −1 for an assumed distance of 8 kpc. There are 17 known X-ray transients within the field of view of our campaign, eight of which were detected in outburst during our observations: the transient neutron star low-mass X-ray binaries GRS 1741-2853, AX J1745.6-2901, SAX J1747.0-2853, KS 1741-293 (all four are also known X-ray bursters), and GRO J1744-28 (a 2.1 Hz X-ray pulsar), and the unclassified X-ray transients XMM J174457-2850.3, CXOGC J174535.5-290124 and CXOGC J174541.0-290014. We present their X-ray spectra and flux evolution during our campaign, and discuss our results in light of their historic activity. Our main results include the detection of two thermonuclear X-ray bursts from SAX J1747.0-2853 that were separated by an unusually short time interval of 3.8 min. Investigation of the lightcurves of AX J1745.6-2901 revealed one thermonuclear X-ray burst and a ∼1600-s long X-ray eclipse. We found that both XMM J174457-2850.3 and GRO J1744-28 displayed weak X-ray activity above their quiescent levels at L X ∼ 10 33−34 erg s −1 , which is indicative of low-level accretion. We compare this kind of activity with the behaviour of low-luminosity X-ray transients that display 2-10 keV peak luminosities of L X ∼ 10 34 erg s −1 and have never been seen to become brighter. In addition to the eight known X-ray transients, we discovered a previously unknown X-ray source that we designate XMMU J174654.1-291542. This object emits most of its photons above 2 keV and appears to be persistent at a luminosity of L X ∼ 10 34 erg s −1 , although it exhibits strong spectral variability on a time scale of months. Based on its X-ray properties and the possible association with an infrared source, we tentatively classify this object as a cataclysmic variable. No new transients were found during our campaign, reinforcing the conclusion of previous authors that most X-ray transients recurring on a time scale of less than a decade have now been identified near the Galactic centre.

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“…However, the energetics of the magnetosphere could limit any emission to a much shorter interval. For comparison, X-ray flares at the Galactic Center are observed with durations of order an hour and X-ray luminosities of ∼ 10 35 erg/s in the energy range 2 − 10 keV [25].…”

Section: B Ns Plummet Into a Smbhmentioning

confidence: 99%

Big black hole, little neutron star: Magnetic dipole fields in the Rindler spacetime

D’Orazio

Levin

2013

Phys. Rev. D

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As a black hole and neutron star approach during inspiral, the field lines of a magnetized neutron star eventually thread the black hole event horizon and a short-lived electromagnetic circuit is established. The black hole acts as a battery that provides power to the circuit, thereby lighting up the pair just before merger. Although originally suggested as an electromagnetic counterpart to gravitational-wave detection, a black hole battery is of more general interest as a novel luminous astrophysical source. To aid in the theoretical understanding, we present analytic solutions for the electromagnetic fields of a magnetic dipole in the presence of an event horizon. In the limit that the neutron star is very close to a Schwarzschild horizon, the Rindler limit, we can solve Maxwell's equations exactly for a magnetic dipole on an arbitrary worldline. We present these solutions here and investigate a proxy for a small segment of the neutron star orbit around a big black hole. We find that the voltage the black hole battery can provide is in the range ∼ 10 16 statvolts with a projected luminosity of 10 42 ergs/s for an M = 10M black hole, a neutron star with a B-field of 10 12 G, and an orbital velocity ∼ 0.5c at a distance of 3M from the horizon. Larger black holes provide less power for binary separations at a fixed number of gravitational radii. The black hole/neutron star system therefore has a significant power supply to light up various elements in the circuit possibly powering bursts, jets, beamed radiation, or even a hot spot on the neutron star crust.

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THE X-RAY FLARING PROPERTIES OF Sgr A* DURING SIX YEARS OF MONITORING WITHSWIFT

Cited by 65 publications

References 59 publications

A systematicChandrastudy of Sgr A^⋆– I. X-ray flare detection

A systematicChandrastudy of Sgr A^⋆– I. X-ray flare detection

A four-yearXMM-Newton/Chandramonitoring campaign of the Galactic centre: analysing the X-ray transients

Big black hole, little neutron star: Magnetic dipole fields in the Rindler spacetime

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THE X-RAY FLARING PROPERTIES OF Sgr A* DURING SIX YEARS OF MONITORING WITHSWIFT

Cited by 65 publications

References 59 publications

A systematicChandrastudy of Sgr A⋆– I. X-ray flare detection

A systematicChandrastudy of Sgr A⋆– I. X-ray flare detection

A four-yearXMM-Newton/Chandramonitoring campaign of the Galactic centre: analysing the X-ray transients

Big black hole, little neutron star: Magnetic dipole fields in the Rindler spacetime

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A systematicChandrastudy of Sgr A^⋆– I. X-ray flare detection

A systematicChandrastudy of Sgr A^⋆– I. X-ray flare detection