Near-infrared observations of GRS 1915+105 in an unusual state with 1.2m Mount Abu telescope

ATel #12806; Joshi, Vishal; Banerjee, Dipankar P. K. (Physical Research Laboratory, Ahmedabad, India)
on 25 May 2019; 09:05 UT
Credential Certification: Vishal Joshi (vjoshi@prl.res.in)

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There has been a sudden dimming in X-rays of the microquasar GRS 1915+105 in recent times accompanied by reports of occasional X-ray flaring (ATel: #11828, #12742, #12743, #12755, #12761, #12793, #12805 and other follow-up telegrams). The source is being monitored across several EM regimes. Near-infrared observations show a Ks band brightening from Ks = 15.59+/-0.03 mag on 6th April 2019 to Ks = 14.77+/-0.02 mag on 12th May 2019 (ATel #12765). Further, there has been a report of a potential dust scattering Halo/Ring, with a radius of ~1 arc minute, in Swift Images of GRS 1915+105 (Atel #12270). We hereby report attempts to detect this ring/halo or possible light-echo in the NIR. Ks band photometry was done with the 1.2m Mount Abu telescope coupled with the Near-infrared Camera/Spectrograph NICS (Banerjee and Ashok, 2012, BASI, 40, 243) which employs a 1024x1024 HgCdTe Hawaii-1 array with an unvignetted 8x8 square arc-minute field-of-view. A series of 400 exposures of 15 seconds each spanning in 3.4 hours were taken on 19 May 2019 (centered around mid-JD of 2458623.36), interspersed with the necessary dithering of the object on the array as required, to yield a total exposure of ~1.8 hours. No evidence of dust emission from a ring or light-echo in seen in the final image down to a limiting magnitude of 16.5 magnitudes in the Ks filter (MKO specification). GRS1915+105 is, however, seen to have brightened significantly to Ks = 12.33+-0.03 in our observations compared to Ks = 14.77 reported on 12 May 2019 in ATel #12765. A light-curve covering the course of our observations is under preparation.