The nucleus of M81 - Simultaneous 2.3 and 8.3 GHz Mark III VLBI observations

Bartel, N.; Shapiro, I. I.; Corey, B. E.; Marcaide, J. M.; Rogers, A. E. E.; Whitney, A. R.; Cappallo, R. J.; Graham, D. A.; Romney, J. D.; Preston, R. A.

doi:10.1086/160447

Cited by 51 publications

(32 citation statements)

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“…Figure 2 displays the time variation of the spectral index, a, deÐned such that where is the Ñux S l P la, S l density at frequency l. As has been well established (de Bruyn et al 1976 ;Bartel et al 1982 ;Reuter & Lesch 1996), the M81 radio core during quiescence has a Ñat to slightly inverted spectrum ; we measure a B 0 to ]0.3 from 2 to 20 cm, consistent with previous determinations.…”

Section: The Light Curvessupporting

confidence: 84%

“…These inconsistencies no doubt reÑect the oversimpliÐcation of the standard model. Realistic modeling of the M81 source, which is beyond the scope of this work, most likely will need to incorporate more complex forms of the particle injection rate (see, e.g., Peterson & Dent 1973), as well as departures from spherical symmetry, since the radio source is known to have an elongated geometry, plausibly interpreted as a core-jet structure (Bartel et al 1982 ;Bartel, Bietenholz, & Rupen 1995 ;Bietenholz et al 1996 ;Ebbers et al 1998). The nuclear jet model of Falcke (1996), for instance, can serve as a useful starting point.…”

Section: The Radio Variability and Its Implicationsmentioning

confidence: 99%

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Discovery of Radio Outbursts in the Active Nucleus of M81

Dyk

Pooley³

et al. 1999

The Astronomical Journal

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The low-luminosity active galactic nucleus of M81 has been monitored at centimeter wavelengths since early 1993 as a by-product of radio programs to study the radio emission from supernova 1993J. The extensive data sets reveal that the nucleus experienced several radio outbursts during the monitoring period. At 2 and 3.6 cm, the main outburst occurred roughly in the beginning of 1993 September and lasted for approximately 3 months ; at longer wavelengths, the maximum Ñux density decreases and the onset of the burst is delayed. These characteristics qualitatively resemble the standard model for adiabatically expanding radio sources, although certain discrepancies between the observations and the theoretical predictions suggest that the model is too simplistic. In addition to the large-amplitude, prolonged variations, we also detected milder changes in the Ñux density at 3.6 cm and possibly at 6 cm on short day) timescales. We discuss a possible association between the radio activity and an optical Ñare ([1 observed during the period that the nucleus was monitored at radio wavelengths.

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Section: The Light Curvessupporting

confidence: 84%

Section: The Radio Variability and Its Implicationsmentioning

confidence: 99%

Discovery of Radio Outbursts in the Active Nucleus of M81

Dyk

Pooley³

et al. 1999

The Astronomical Journal

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“…Its central region has Seyfert and LINER (2) characteristics (3)(4)(5) and an inferred size at optical wavelengths smaller than 10 milliarsec (mas) (6). It harbors a variable x-ray source (7,8) and a radio core with a flat or slightly inverted radio spectrum (9,10), which is variable on time scales of days (6), extremely compact (10)(11)(12), and elongated with a frequency-dependent size along its major axis of 0.4 mas at 8.3 GHz (10). At a distance of -4 megaparsec (Mpc; 1 pc = 3.09 x 1016 m) (13,14) the linear size of the radio core is as small as 1500 astronomical units (AU) (at 8.3 GHz), which makes it the most compact extragalactic nucleus of which the size has yet been measured.…”

Section: Introductionmentioning

confidence: 99%

The nuclear region of the spiral galaxy M81.

Bartel¹,

Bietenholz²,

Rupen³

1995

Proc. Natl. Acad. Sci. U.S.A.

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“…The nucleus is exceptionally compact: 700 AU x 300 AU at 22 GHz, with the size being proportional to v~0-8 (Bietenholz et al 1996;Bartel et al 1995;Bartel et al 1982; see also Kellermann et al 1976). Here we present further results from new VLA and VLBI observations of the nucleus of M81.…”

Section: Introductionmentioning

confidence: 99%