Evidence of a Dust Scattering Halo/Ring in Swift Images of GRS 1915+105

ATel #12770; L. Corrales, M. Balakrishnan, M. Reynolds, J. M. Miller (Univ. of Michigan)
on 17 May 2019; 01:02 UT
Credential Certification: Jon Miller (jonmm@umich.edu)

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We have been monitoring the recent low flux state of the iconic stellar-mass black hole GRS 1915+105 with a number of telescopes, including the Neil Gehrels Swift Observatory. Other recent reports on this low flux state include ATEL #12742, #12743, #12755, #12761, #12765, #12769.

The most recent observation, 00034292138, was obtained on 2019 May 16 starting at 10:10:44 UT. The flux of the source appears to have dropped below 1 E-10 erg/cm2/s to (3.5 +- 0.2) E-11 erg/cm2/s, providing a fairly clean image in the Swift/XRT in photon counting mode.

The raw image in the full band shows some evidence of extension that becomes more prominent when the data are smoothed. Filtering to create a 1-4 keV image, and smoothing by 3-5 pixels, there is evidence of a dust-scattering ring at a radius of approximately 65 arc seconds. This ring could be the result of the strong flaring seen in the prior few days (see ATEL #12761). If caused by the abrupt flares on 2019 May 14, the ring arises from dusty material at an approximate distance of (5.7 +/- 1.3) kpc, using the distance of (8.6 +/- 2) kpc to GRS 1915+105 (Reid et al. 2014).

An image of the potential scattering ring can be found here:

https://sites.lsa.umich.edu/jonmm/2019/05/16/a-dust-scattering-ring-in-grs-1915105

We thank the Neil Gehrels Swift Observatory for executing high-cadence monitoring of GRS 1915+105 in this unusual flux state.

References:
Reid, M., et al., 2014, ApJ, 796, 2