Nova Sgr 2010b (V5586 Sgr) caught during eruption by VVV observations

ATel #4353; R. K. Saito (Pontificia Universidad Catolica de Chile, Universidad de Valparaiso, The Milky Way Millennium Nucleus) and D. Minniti (Pontificia Universidad Catolica de Chile)
on 5 Sep 2012; 14:22 UT
Credential Certification: Roberto Saito (rsaito@astro.puc.cl)

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Nova Sgr 2010b (V5586 Sgr) was discovered in eruption by K. Nishiyama and F. Kabashima (CBET 2261; IAUC 9140 ), with 11.2 mag in unfiltered light on Apr 23.782 2010 UT. The nova was reported with coordinates RA 17:53:02.99 DEC -28:12:19.4 (J2000). The VISTA Variables in Via Lactea Survey (VVV) is mapping the Galactic Bulge and Southern plane in the near-infrared with the VISTA telescope at ESO's Cerro Paranal Observatory since March 2010 (vvvsurvey.org; Minniti et al. 2010, New Astronomy, 15, 433). VVV observations taken on April 23 2010 caught Nova Sgr 2010b during eruption, about half day before the first observation reported by Nishiyama and Kabashima. A Ks-band observation taken on Apr 23.2479 2010 UT shows Nova Sgr 2010b as a stellar source with Ks=10.609+/-0.010, while in a J-band observation on Apr 23.2501 2010 UT the object appeared as a saturated source with J=7.764+/-0.010. Taking into consideration novae usually have (J-Ks)>0, one can conclude that the VVV observations caught Nova Sgr 2010b rising during eruption. A complementary observation taken on Sep 12 2010 shows the object with Ks=12.581+/-0.015. Nova Sgr 2010b faded beyond detection in several Ks-band observations taken from Sep 2011 to Apr 2012, allowing us to infer that the object dropped to Ks>16.3, the VVV limiting magnitude in this field. Nova Sgr 2010b is the innermost nova in the Galaxy. The VVV coordinates for the target are RA 17:53:02.98 DEC -28:12:18.84 (J2000), corresponding to (l,b)=(1.466, -1.023).