A four-year baseline<i>Swift</i>study of enigmatic X-ray transients located near the Galactic center

Degenaar, N.; Wijnands, Rudy

doi:10.1051/0004-6361/201015322

Cited by 71 publications

(113 citation statements)

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“…On the other hand, (Degenaar & Wijnands 2010;Degenaar et al 2012) detected 17 transients within the central 1.2 deg 2 of the GC based on long term monitoring programs of the GC region using Chandra and Swift. These programs cover more or less the complete sample of the BH or NS XBs with recurring bursts on a timescale of less than a decade.…”

Section: ) (A-mentioning

confidence: 99%

NuSTAR HARD X-RAY SURVEY OF THE GALACTIC CENTER REGION. II. X-RAY POINT SOURCES

Hong

Mori

Hailey

et al. 2016

ApJ

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We present the first survey results of hard X-ray point sources in the Galactic Center (GC) region by NuSTAR. We have discovered 70 hard (3-79 keV) X-ray point sources in a 0.6 deg 2 region around SgrA * with a total exposure of 1.7 Ms, and 7 sources in the SgrB2 field with 300 ks. We identify clear Chandra counterparts for 58 NuSTAR sources and assign candidate counterparts for the remaining 19. The NuSTAR survey reaches X-ray luminosities of ∼4× and ∼8×10 32 erg s -1 at the GC (8 kpc) in the 3-10 and 10-40 keV bands, respectively. The source list includes three persistent luminous X-ray binaries (XBs) and the likely run-away pulsar called the Cannonball. New source-detection significance maps reveal a cluster of hard (>10 keV) X-ray sources near the SgrA diffuse complex with no clear soft X-ray counterparts. The severe extinction observed in the Chandra spectra indicates that all the NuSTAR sources are in the central bulge or are of extragalactic origin. Spectral analysis of relatively bright NuSTAR sources suggests that magnetic cataclysmic variables constitute a large fraction (>40%-60%). Both spectral analysis and logN-logS distributions of the NuSTAR sources indicate that the X-ray spectra of the NuSTAR sources should have kT>20 keV on average for a single temperature thermal plasma model or an average photon index of Γ=1.5-2 for a power-law model. These findings suggest that the GC X-ray source population may contain a larger fraction of XBs with high plasma temperatures than the field population.

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Section: ) (A-mentioning

confidence: 99%

NuSTAR HARD X-RAY SURVEY OF THE GALACTIC CENTER REGION. II. X-RAY POINT SOURCES

Hong

Mori

Hailey

et al. 2016

ApJ

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“…Here, Z is the metallicity assumed for the MC, R the radius of the cloud as seen from Sgr A* (pc), F 6.4 the flux measured in the Fe-K α line (photons/cm 2 /s), Ω the solid angle (scaled to the whole sky, in units of 10 binary source close to or even within the AC. Then the requirement is for the bright state to have lasted for more than 8 years at or above L x ∼ 10 37 erg/s; this is much longer than the typical flaring timescales of X-ray transient sources (e.g., Degenaar & Wijnands 2010).…”

Section: The Xrn Hypothesismentioning

confidence: 99%

Fe Kαline emission from the Arches cluster region – evidence for ongoing particle bombardment?

Capelli¹,

Warwick²,

Porquet³

et al. 2011

A&A

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Context. Bright Fe-K α line emission at 6.4 keV is a unique characteristic of some of the dense molecular complexes present in the Galactic center region. Whether this X-ray fluorescence is due largely to the irradiation of the clouds by X-ray photons or is, at least in part, the result of cosmic-ray particle bombardment, remains an interesting open question. Aims. We present the results of XMM-Newton observations performed over the last eight years of the region surrounding the Arches cluster in the Galactic center. We study the spatial distribution and temporal behaviour of the Fe-K α emission with the objective of identifying the likely source of the excitation. Methods. We have constructed an Fe-K α fluence map in a narrow energy band of width 128 eV centered on 6.4 keV. We use this to localize the brightest fluorescence features in the vicinity of the Arches cluster. We have investigated the variability of the 6.4-keV line emission of several clouds through spectral fitting of the EPIC MOS data with the use of a modelled background, which avoids many of the systematics inherent in local background subtraction. We also employ spectral stacking of both EPIC PN and MOS data to search for evidence of an Fe-K edge feature imprinted on the underlying X-ray continuum.Results. The lightcurves of the Fe-K α line emission from three bright molecular knots close to the Arches cluster were found to be constant over the 8-year observation window. However, West of the cluster, we found a bright cloud which shows the fastest Fe-K α variability yet seen in a molecular cloud in the Galactic center region. The time averaged spectra of the molecular clouds revealed no convincing evidence of the 7.1-keV edge feature, albeit with only weak constraints. The EW of the 6.4-keV line emitted by the clouds near to the cluster was found to be ∼1.0 keV. Conclusions. The observed Fe-K α line flux and the high value of the EW suggest an origin of the fluorescence in the photoionization of the MCs by X-ray photons, although excitation by cosmic-ray particles is not specifically excluded. For the three clouds nearest to the Arches cluster, the identification of the source of these X-rays as an earlier outburst on Sgr A* is at best tentative, although not entirely ruled out by the observations. On the other hand, the hardness of the nonthermal component associated with the 6.4-keV line emission might be best explained in terms of the bombardment of the clouds by cosmic-ray particles emanating from the Arches cluster itself. The relatively short-timescale variability seen in the 6.4-keV line emission from the cloud to the west of the cluster is most likely the result of its X-ray illumination by a nearby transient X-ray source.

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“…X-ray binaries with peak LX in the range 10 34 -10 36 ergs/s are known as very-faint X-ray binaries (VFXBs). The low time-averaged accretion luminosity of VFXBs is hard to explain in binary evolution models, since it is difficult to reach masstransfer rates this low via standard LMXB binary evolution within the age of the universe (King & Wijnands 2006;Degenaar & Wijnands 2010;Maccarone & Patruno 2013).…”

Section: Introductionmentioning

confidence: 99%

“…Degenaar & Wijnands 2010). Furthermore, VFXB outbursts can be produced by a range of objects, including high-mass X-ray binaries (Torii et al 1998), symbiotic X-ray binaries (Masetti et al 2007), and cataclysmic variables (Mukai et al 2008;Stacey et al 2011).…”

Section: Introductionmentioning

confidence: 99%

The 2013 outburst of a transient very faint X-ray binary, 23 arcsec from Sgr A*

Koch¹,

Bahramian²,

Heinke³

et al. 2014

Monthly Notices of the Royal Astronomical Society

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We report observations using the Swift/XRT, NuSTAR, and Chandra X-ray telescopes of the transient X-ray source CXOGC J174540.0-290005, during its 2013 outburst. Due to its location in the field of multiple observing campaigns targeting Sgr A*, this is one of the best-studied outbursts of a very faint X-ray binary (VFXB; peak L X < 10 36 erg/s) yet recorded, with detections in 173 ks of X-ray observations over 50 days. VFXBs are of particular interest, due to their unusually low outburst luminosities and time-averaged mass transfer rates, which are hard to explain within standard accretion physics and binary evolution. The 2013 outburst of CXOGC J174540.0-290005 peaked at L X (2-10 keV)=5.0 × 10 35 erg/s, and all data above 10 34 ergs/s were well-fit by an absorbed power-law of photon index ∼ 1.7, extending from 2 keV out to > ∼ 70 keV. We discuss the implications of these observations for the accretion state of CXOGC J174540.0-290005.

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A four-year baselineSwiftstudy of enigmatic X-ray transients located near the Galactic center

Cited by 71 publications

References 45 publications

NuSTAR HARD X-RAY SURVEY OF THE GALACTIC CENTER REGION. II. X-RAY POINT SOURCES

NuSTAR HARD X-RAY SURVEY OF THE GALACTIC CENTER REGION. II. X-RAY POINT SOURCES

Fe Kαline emission from the Arches cluster region – evidence for ongoing particle bombardment?

The 2013 outburst of a transient very faint X-ray binary, 23 arcsec from Sgr A*

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