ALMA/NICER observations of GRS 1915+105 indicate a return to a hard state

Abstract

Context. GRS 1915+105 is a transient black hole X-ray binary consistently emitting 10–100% of the Eddington luminosity in the X-ray band over the last three decades until mid-2018 when the source luminosity suddenly decreased by an order of magnitude. This phase was followed by a change to a state with even lower average X-ray fluxes never seen before during the outburst but presenting renewed flaring activity at different wavelengths, albeit with mean fluxes still in decline. Aims. GRS 1915+105 has the longest orbital period known among low-mass X-ray binaries, the largest accretion disk size, and therefore the largest mass supply for accretion. The high inclination of the disk allows the study of geometrical effects of the accretion flow such as changes in the height-to-radius ratio or the effect of accretion disk winds on the intrinsic emission that is expected during the outburst decay. In addition, the transient jet is expected to change to a compact, self-absorbed, steady jet. Methods. We conducted two full polarization Atacama Large Millimeter Array observations to study the jet properties during the outburst decay by analyzing the spectral, polarization, and intra-epoch variability for both observation epochs. In addition, we analyzed almost daily Neutron Star Interior Composition Explorer pointing observations, modeling X-ray power spectral densities, spectral energy distributions, and light curves with a physically motivated model to follow the changing accretion disk properties throughout the outburst decay and relating them to the jet emission. Results. We show that the X-ray and millimeter (mm) spectral, timing, and polarization properties are consistent with those of a typical decaying X-ray binary outburst and that GRS 1915+105 has descended into the low-luminosity hard X-ray state. The jet emission in the mm is consistent with a compact, steady jet with ∼1% linear polarization, and the magnetic field is likely aligned with the jet position angle. Relating the mm emission to the X-ray emission reveals that the source has changed from a higher radio/X-ray correlation index to a lower one; Lradio ∝ LX0.6.

On Its Way to the Neutron Star–White Dwarf Binary Graveyard, IGR J16194−2810, A First Ascent M Giant X-Ray Binary

“…One possible explanation is absorption of the X-ray flux by the circum-NS accretion disk. Koljonen & Hovatta (2021) note that longer orbital periods in LMXBs translate into larger Roche lobes and larger accretion disk sizes. Koljonen & Tomsick (2020) discuss several systems with large accretion disks at high orbital inclination that have intrinsic X-ray luminosities much lower than the Eddington luminosity as a result of heavy obscuration.…”

QPOML: a machine learning approach to detect and characterize quasi-periodic oscillations in X-ray binaries

“…On one hand, GRS 1915 + 105 has long been known as a markedly unusual source in terms of its outb urst beha viours and states (e.g. its very abnormal, three-decade long transient outburst, re gular/irre gular bursts, dips, etc., behaviors influenced by GRS 1915 + 105's orbital period and accretion disc size, the longest and largest respectively known among LMXRBs), wheres on the other hand, MAXI J1535 −571 is, in comparison to GRS 1915 + 105, a far more typical source in terms of outburst states, QPO-spectral parameter associations, and tracks through the hardness-intensity diagram (Taam, Chen & Swank 1996 ;Truss & Done 2006 ;Nakahira et al 2018 ;Bhargava et al 2019 ;C úneo et al 2020 ;Koljonen & Hovatta 2021 ;Garc ía et al 2022a ). Hence, between these two sources we aim to e v aluate our methods across a spectrum of typical to challenging spectral-timing relationships.…”

Matter ejections behind the highs and lows of the transitional millisecond pulsar PSR J1023+0038

“…The millimetre emission is unresolved, implying a size for the emission region smaller than ≈6 × 10 15 cm (this corresponds to ≈7 × 10 4 times the orbital separation of the system; Archibald et al 2013). Millimetre/sub-millimetre continuum emission has been firmly detected from a number of transiently accreting stellarmass black holes (Paredes et al 2000;Ogley et al 2000;Fender et al 2000Fender et al , 2001Ueda et al 2002;Russell et al 2013aRussell et al , 2020van der Horst et al 2013;Tetarenko et al 2015Tetarenko et al , 2017Tetarenko et al , 2019Tetarenko et al , 2021de Haas et al 2021;Koljonen & Hovatta 2021;Díaz Trigo et al 2021) and in three accreting NSs so far: the persistent systems 4U 1728−34 and 4U 1820−30 (Díaz Trigo et al 2017) and the transient accreting millisecond pulsar Aql X-1 (Díaz Trigo et al 2018). In these cases, however, such emission has been detected during accretion states that are seemingly different from the X-ray sub-luminous disc state attained by J1023 at the epoch of our ALMA observations, as detailed below.…”