A Transient Radio Source near the Center of the Milky Way Galaxy

Zhao, Jun‐Hui; Roberts, D. A.; Goss, W. M.; Frail, D. A.; Lo, K. Y.; Subrahmanyan, R.; Kesteven, M. J.; Ekers, R. D.; Allen, D. A.; Burton, M. G.; Spyromilio, J.

doi:10.1126/science.255.5051.1538

Cited by 51 publications

(43 citation statements)

References 27 publications

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“…There are many lines of sight through the interstellar medium for which anisotropic turbulence has been proposed, primarily based upon measurement of very elliptical scattering disks (Spangler & Cordes 1988 ;Wilkinson et al 1994 ;Frail et al 1994 ;YusefZadeh et al 1994 ;Desai et al 1994 ;Molnar et al 1995 ;Rickett, Lyne, & Gupta 1997 ;Trotter et al 1998 ;Spangler & Cordes 1998). There are also many lines of sight where nominally elliptical scattering disks have been seen but not attributed to anisotropic turbulence (Spangler, Fey, & Cordes 1987 ;Gwinn et al 1988 ;Fey et al 1989 ;Zhao et al 1992 ;Fey & Mutel 1993). The interpretation of mildly elliptical scattering disks is especially difficult since both di †rac-tive and refractive e †ects can have comparable contributions.…”

Section: Turbulence and Interstellar Scatteringmentioning

confidence: 99%

Anisotropic Interstellar Scattering toward the Cygnus Region

Desai¹,

Fey²

2001

ASTROPHYS J SUPPL S

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We were unable to reliably determine scattering disk parameters for 2021]317 at frequencies from 8.5 GHz down to 1.67 GHz because of its complex intrinsic source structure. The scattering disks are elliptical with axial ratios of about 0.75 : 1 with little measurable variation between these sources. We interpret our measurements as due to the e †ects of anisotropic interstellar turbulence. The anisotropy parameters, axial ratio and position angle, for those sources for which we have data at multiple frequencies appear to be frequency-independent making refractive distortions of isotropic turbulence an unlikely explanation. Our estimates of b, the power-law index of the power spectrum of electron density Ñuctuations, based upon direct model Ðts to the data on a source-by-source and frequency-by-frequency basis, are consistent with b \ 4 for most of the data but are strongly a †ected by our estimate of the intrinsic structure of the sources. Two of these sources, 2005]403 and 2021]317, exhibit signiÐcant intrinsic source structure at frequencies as low as 1.67 GHz, while the other two, 2008]332 and 2048]312, lack discernible source structure at frequencies lower then 2.3 GHz. The frequency scalings of the scattered angular sizes are also consistent with b \ 4. We discuss the implications of our measurements for the inner and outer scales of the turbulence.

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Section: Turbulence and Interstellar Scatteringmentioning

confidence: 99%

Anisotropic Interstellar Scattering toward the Cygnus Region

Desai¹,

Fey²

2001

ASTROPHYS J SUPPL S

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“…Theoretical estimates also suggest that as many as 2 × 10 4 stellar mass black holes could reside in the inner parsec as a result of similar processes (Miralda-Escudé & Gould 2000). Furthermore, previous detections of radio transients in the Galactic center (Zhao et al 1992;Hyman et al 2005Hyman et al , 2009Bower et al 2005) and a radio-emitting magnetar near Sgr A* (Mori et al 2013;Shannon & Johnston 2013;Eatough et al 2013) suggest that the high density of objects does enable the detection of novel transient activity. Regardless of the exact nature of any transient phenomena, the exploration of radio transients on timescales from seconds to minutes presents a useful bridge between previous archival imaging searches (τ days) and more recent fast imaging searches for millisecond transients (Law et al 2015).…”

Section: Introductionmentioning

confidence: 88%

Transient Events in Archival Very Large Array Observations of the Galactic Center

Chiti

Chatterjee

Wharton

et al. 2016

ApJ

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The Galactic center has some of the highest stellar densities in the Galaxy and a range of interstellar scattering properties that may aid in the detection of new radio-selected transient events. Here we describe a search for radio transients in the Galactic center using over 200 hours of archival data from the Very Large Array (VLA) at 5 and 8.4 GHz. Every observation of Sgr A* from 1985−2005 has been searched using an automated processing and detection pipeline sensitive to transients with timescales between 30 seconds and five minutes with a typical detection threshold of ∼100 mJy. Eight possible candidates pass tests to filter false-positives from radio-frequency interference, calibration errors, and imaging artifacts. Two events are identified as promising candidates based on the smoothness of their light curves. Despite the high quality of their light curves, these detections remain suspect due to evidence of incomplete subtraction of the complex structure in the Galactic center, and apparent contingency of one detection on reduction routines. Events of this intensity (∼100 mJy) and duration (∼100 s) are not obviously associated with known astrophysical sources, and no counterparts are found in data at other wavelengths. We consider potential sources, including Galactic center pulsars, dwarf stars, sources like GCRT J1745−3009, and bursts from X-ray binaries. None can fully explain the observed transients, suggesting either a new astrophysical source or a subtle imaging artifact. More sensitive multiwavelength studies are necessary to characterize these events which, if real, occur with a rate of 14 +32 −12 hr −1 deg −2 in the Galactic center.

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“…Assuming that GCRT J1746À2757 decayed according to a power law (S / [t À t 0 ] ) with the same index as the GCT, = À0.67 (Zhao et al 1992), and that the peak occurred no later than 1 day prior to our detection, we would expect its 1.4 GHz flux density to have been no less than about 1 mJy in 2000 December. Since the noise level of our 2000 December 11 follow-up 1.4 GHz observations was much less (0.08 mJy beam À1 ) than this extrapolated value, we conclude that GCRT J1746À2757 decayed much faster than the GCT, its spectrum was steeper, or both.…”

Section: Gcrt J1746à2757mentioning

confidence: 99%

“…For frequencies between 1.36 and 1.67 GHz, the GCT decreased to approximately 12% of its peak flux density in only a month (Zhao et al 1992). The only detection of the radio counterpart to A1742À28 was made on 1975 March 30 at 0.96 GHz, followed by nondetections on 1975 May 3 and June 20 at 0.408 and 0.96 GHz, respectively.…”

Section: Gcrt J1746à2757mentioning

confidence: 99%

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Low-Frequency Radio Transients in the Galactic Center

Hyman

Lazio

Kassim

et al. 2002

The Astronomical Journal

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We report the detection of a new radio transient source, GCRT J1746À2757, located only 1=1 north of the Galactic center. Consistent with other radio transients toward the Galactic center, this source brightened and faded on a timescale of a few months. No X-ray counterpart was detected. This suggests that either there was only very faint X-ray emission, compared with highly Doppler boosted radio emission, or that GCRT J1746À2757 is a member of a class of radio transients with no associated X-ray emission. We also report new 0.33 GHz measurements of the radio counterpart to the X-ray transient source, XTE J1748À288, previously detected and monitored at higher radio frequencies. We show that the spectrum of XTE J1748À288 steepened considerably during a period of a few months after its peak. We also discuss the need for a more efficient means of finding additional radio transients.

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A Transient Radio Source near the Center of the Milky Way Galaxy

Cited by 51 publications

References 27 publications

Anisotropic Interstellar Scattering toward the Cygnus Region

Anisotropic Interstellar Scattering toward the Cygnus Region

Transient Events in Archival Very Large Array Observations of the Galactic Center

Low-Frequency Radio Transients in the Galactic Center

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