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ATEL # 1305; M.P. Rupen, V. Dhawan, A.J. Mioduszewski (NRAO)
on 26 Nov 2007; 23:33 UT
Password Certification: Michael P. Rupen (firstname.lastname@example.org)
Subjects: Radio, X-ray, Nova, Transients
Observations with the Very Large Array (VLA) in its moderately extended 'B' configuration give strong detections of the nova V598 Pup = XMMSL1 J070542.7-381442) (ATel #1282, #1285, #1301) on Nov. 18 (4.86 GHz: 4.45 +/- 0.07 mJy; 8.46 GHz: 10.85 +/- 0.06 mJy) and Nov. 21 (8.46 GHz: 10.55 +/- 0.07 mJy). The sharply rising spectrum, with flux density going as frequency to the +1.6 power, suggests this is thermal bremsstrahlung emission, as often seen in novae (e.g., Hjellming et al. 1979, AJ 84, 1619).
The source is unresolved in these images, which had a resolution at 8.4 GHz of about 3.2 x 0.8 arcsec, oriented roughly north-south. Gaussian fits yield an upper limit to the source size of 0.5 x 0.18 arcsec at 8.46 GHz, corresponding to a minimum brightness temperature of about 2000 K. If the emission were optically thick, and the physical gas temperature of order 10,000 K, the source diameter required to give the observed flux density would be about 0.14 arcseconds.
The observed position agrees perfectly with that of the proposed progenitor, USNO-A2.0 0450-03360039 (ATel #1282, #1285). The radio position, as measured under good weather conditions via Gaussian fits at 8.46 GHz, is 07 05 42.5067, -38 14 39.48 (J2000). This position is measured with respect to the nearby (4.9 degrees) extragalactic calibrator J0729-3639, and is consistent to the quoted number of significant figures between the two days. The error bar is likely rather larger, due to systematic effects, and may be taken conservatively as perhaps a tenth of the resolution.
Further VLA observations are on-going.
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