A large misalignment between continuous jet and discrete ejecta in microquasar GRS 1915+105 during its obscured phase

Abstract

We report a large misalignment between the continuous jet and the discrete ejecta in GRS 1915+105, detected in April 2023 with the East Asian VLBI network (EAVN). Two-sided ejecta are shown at 6.7 GHz images and central continuous jets are resolved at 43 GHz by EAVN quasi-simultaneously. While the continuous jet was aligned with the long-standing jet position angle (PA) of about 147 degree, the discrete ejecta appeared at a markedly different PA about 188 degree, with the lowest intrinsic velocity about 0.35 c ever reported. A similar misalignment of PA between discrete ejecta and continuous jet was independently detected in late September of 2023 during a consecutive flare event. The pronounced and recurrent angular deviations suggest a time-variable jet launching geometry, which, in conjunction with the observed X-ray obscuration, can be attributable to a warped accretion disk. Our result could offer new insight into the fundamental differences between continuous jet and discrete ejecta, and broadly provides a clue to understand the phenomena for transient black hole X-Ray binaries and changing-look active galactic nuclei during the X-ray obscured phase.

Figures (3)

• Figure 1: Large misalignment of position angles between continuous jets and discrete ejecta in GRS 1915+105. Radio images are obtained by the East Asian VLBI Network (EAVN) in the left and the Karl G. Jansky Very Large Array (VLA) in the right, with the image parameters summarized in \ref{['table:GRS1915_modelfit_EAVN_data']}. At the distance of GRS 1915+105 ($\sim9.4$ kpc), 1 mas corresponds to 9.4 AU here. The two-sided blobs at both 6.7 GHz of EAVN and 10 GHz of VLA are recognized as discrete ejecta. The extended structure at 43 GHz of EAVN and the center of VLA are continuous jets. The FWHM of synthesized beams are around $6\,\text{mas}\times3\,\text{mas}$ and $0.9\,\text{mas}\times0.5\,\text{mas}$ for the EAVN at 6.7 GHz (blue) and 43 GHz (red), respectively. It is about $160\,\text{mas}\times150\,\text{mas}$ for the VLA at 10 GHz (grey). Contours in the three frequencies start at four times the image rms noise levels of 0.8, 5.0, and 0.3 mJy beam$^{-1}$, respectively, and increase by factors of two. The PA directions of main two-sided ejecta (S1 and N1) from EAVN images at 6.7 GHz: PA $\sim 192^\circ$, $\sim 186^\circ$, and $\sim 186^\circ$ on April 15, 2023, April 17, 2023, and April 23, 2023, respectively. The dashed lines are linear fitting to radial distances of the S1 and N1 components as a function of time (see \ref{['table:GRS1915_modelfit_EAVN_data']}). The apparent speeds are $6.50 \pm 0.18$ mas d$^{-1}$ for S1 and $6.53 \pm 0.19$ mas d$^{-1}$ for N1, respectively. Extrapolation further indicates that both components were ejected around MJD 60045. The PA of continuous jets from EAVN 43 GHz data: PA $\sim 158^\circ$, and $\sim 146^\circ$ on April 16, 2023 and April 19, 2023, respectively; PA $\sim 174^\circ$ and $\sim 148^\circ$ for the discrete ejecta (S2 and N2) and center continuous jet are indicated by dotted lines from VLA 10 GHz data on September 30, 2023, respectively.
• Figure 2: Top: schematic plots of warped disk and continuous jet or ejecta in GRS 1915+105 generated with Nano Banana Pro. The long-standing jet axis is represented by the left of the second panel, the warped disk producing ejecta at a different direction is in the middle, and the inner disk aligned to BH spin producing the continuous jet is on the right. As the inner disk is aligned quickly, both the early launched discrete ejecta and the continuous jet could be seen in the same image. Bottom: the snapshots for the disk around the BH (centered at the origin) perturbed by a flyby object in a parabolic orbit. Three panels show the density contour at the $x-y$, $y-z$, and $x-y$ plane right after the object passes pericenter.
• Figure 3: Phase-referenced images of GRS 1915+105 observed with EAVN at 6.7 GHz on April 15 (left), 17 (middle), and 23 (right), 2023. Contours start at 0.5 mJy beam$^{-1}$, increasing by factors of 2. The synthesized beam is indicated in the bottom-left corner of each panel. The J2000 coordinates of the map center (0,0) are ($19^{\rm h}15^{\rm m}11\hbox{.}^{\rm s}5473$, $+10^{\circ}56^{'}44\hbox{.}^{"}7040$), corresponding to the source positions at an epoch within 2007--2008. The red cross marks the expected source position in 2023, ($19^{\rm h}15^{\rm m}11\hbox{.}^{\rm s}54409$ mas, $+10^{\circ}56^{'}44\hbox{.}^{"}6044$ mas), extrapolated from proper motion estimates. These results suggest the detection of a bright, compact core of GRS 1915+105 in our phase-referenced images.