The Sloan Digital Sky Survey V (SDSS-V) is pioneering panoptic spectroscopy: it is the first all-sky, multiepoch, optical-to-infrared spectroscopic survey. SDSS-V is mapping the sky with multiobject spectroscopy (MOS) at telescopes in both hemispheres (the 2.5 m Sloan Foundation Telescope at Apache Point Observatory and the 100-inch du Pont Telescope at Las Campanas Observatory), where 500 zonal robotic fiber positioners feed light from a wide-field focal plane to an optical ( R ∼ 2000, 500 fibers) and a near-infrared ( R ∼ 22,000, 300 fibers) spectrograph. In addition to these MOS capabilities, the survey is pioneering ultra–wide-field (∼4000 deg ² ) integral field spectroscopy enabled by a new dedicated facility (LVM-I) at Las Campanas Observatory, where an integral field spectrograph (IFS) with 1801 lenslet-coupled fibers arranged in a 0 . ° 5-diameter hexagon feeds multiple R ∼ 4000 optical spectrographs that cover 3600–9800 Å. SDSS-V’s hardware and multiyear survey strategy are designed to decode the chemodynamical history of the Milky Way and tackle fundamental open issues in stellar physics in its Milky Way Mapper program, trace the growth physics of supermassive black holes in its Black Hole Mapper program, and understand the self-regulation mechanisms and the chemical enrichment of galactic ecosystems at the energy injection scale in its Local Volume Mapper program. The survey is well timed to multiply the scientific output from major all-sky space missions. The SDSS-V MOS programs began robotic operations in 2021; IFS observations began in 2023 with the completion of the LVM-I facility. SDSS-V builds on decades of heritage of SDSS’s pioneering advances in data analysis, collaboration spirit, infrastructure, and product deliverables in astronomy.

We present spectral and timing properties of the newly discovered X-ray transient source, MAXI J1535-571, which is believed to be a Galactic X-ray binary containing a black hole candidate (BHC) as the primary object. Since its discovery on 2017 September 2, it has been monitored regularly in multi-wavelength bands by several satellites. We use archival data of the Swift (XRT and BAT) and MAXI (GSC) satellite instruments to study accretion flow dynamics of the source during the outburst. During its outburst, the source became very bright in the sky with a maximum observed flux of 5 Crab in the 2–10 keV GSC band. Similar to other transient BHCs, it also shows signatures of low-frequency quasi-periodic oscillations (QPOs) during the outburst. Spectral data of different instruments are fitted with the transonic flow, solution-based two-component advective flow model fits file to find the direct accretion flow parameters. The evolution of spectral states and their transitions are understood from the model-fitted physical flow parameters and nature of QPOs. We also estimate the probable mass of the black hole from our spectral analysis as 7.9–9.9 M _⊙ or 8.9 ± 1.0 M _⊙.

The Galactic transient X-ray binary MAXI J1836-194 was discovered on 2011 August 29. Here we make a detailed study of the spectral and timing properties of its 2011 outburst using archival data from the RXTE Proportional Counter Array instrument. The evolution of accretion flow dynamics of the source during the outburst through spectral analysis with Chakrabarti–Titarchuk’s two-component advective flow (TCAF) solution as a local table model in XSPEC. We also fitted spectra with combined disk blackbody and power-law models and compared it with the TCAF model fitted results. The source is found to be in hard and hard-intermediate spectral states only during the entire phase of this outburst. No soft or soft-intermediate spectral states are observed. This could be due to the fact that this object belongs to a special class of sources (e.g., MAXI J1659-152, Swift J1753.5-0127, etc.) that have very short orbital periods and that the companion is profusely mass-losing or the disk is immersed inside an excretion disk. In these cases, flows in the accretion disk are primarily dominated by low viscous sub-Keplerian flow and the Keplerian rate is not high enough to initiate softer states. Low-frequency quasi-periodic oscillations (QPOs) are observed sporadically although as in normal outbursts of transient black holes, monotonic evolutions of QPO frequency during both rising and declining phases are observed. From the TCAF fits, we find the mass of the black hole in the range of 7.5–11 M _⊙, and from time differences between peaks of the Keplerian and sub-Keplerian accretion rates we obtain a viscous timescale for this particular outburst, ∼10 days.

The Galactic transient black hole candidate (BHC) MAXI J1659−152 exhibited temporal and spectral evolution during its very first X-ray outburst (2010) after its discovery on 2010 September 25. Our recent studies of a few transient BHCs, including MAXI J1659−152, using the Chakrabarti–Titarchuk two-component advective flow (TCAF) solution as an additive table local model in the xspec software revealed details of the accretion-flow dynamics around the black holes. The TCAF model-fitted normalization (N) comes out to be almost constant throughout the entire outburst, consisting of several spectral states. We introduce two independent methods to determine the mass (M_BH) of the BHC: namely (i) keeping the TCAF fitted normalization parameter in a narrow range and (ii) studying the evolution of the quasi-periodic oscillation frequency (ν_QPO) with time, fitting with the propagating oscillatory shock (POS) model. The predicted mass ranges of the source with these two methods are 4.7–7.8 M_⊙ and 5.1–7.4 M_⊙, respectively. Combining the results of these two methods, we obtain a most probable mass range of the source of 4.7–7.8 M_⊙ or $$6^{+1.8}_{-1.3}\,\mathrm{M}_{{\odot }}$$.

We derive accretion flow properties of the transient black hole candidate (BHC) MAXI J1543–564 using the RXTE data. We use the two-component advective flow (TCAF) solution to fit the data of the initial rising phase of outburst (from 2011 May 10 to 15). The 2.5–25 keV spectra are fitted using the TCAF solution fits file as a local additive table model in XSPEC. We extract physical flow parameters such as the two-component (Keplerian disk and sub-Keplerian halo) accretion rates and size and the property of the Compton cloud (post-shock region close to a black hole). Similar to other classical transient BHCs, monotonic evolution of low-frequency quasi-periodic oscillations (QPOs) is observed during the rising phase of the outburst, which is fitted with the propagating oscillatory shock (POS) model, which describes how the Compton cloud properties change from day to day. From the nature of variations of TCAF model fitted physical flow parameters and QPOs, we only found hard-intermediate and soft-intermediate spectral states during this phase of the outburst under study. We also calculated the frequency of the dominating QPOs from the TCAF model fitted shock parameters and found that they roughly match with the observed and POS model fitted values. From our spectro-temporal study of the source with TCAF and POS models, the most probable mass of the BHC is found to be 12.6–14.0 M _⊙, or .

We present the results obtained from broad-band X-ray timing and spectral analysis of black hole (BH) candidate MAXI J1803–298 using an AstroSat observation on 2021 May 11–12. Four periodic absorption dips with a periodicity of 7.02 ± 0.18 h are detected in the light curve. AstroSat observe the source when it was undergoing a transition from hard-intermediate state to soft-intermediate state. Our timing analysis reveals the presence of a sharp Type-C quasi-periodic oscillation (QPO) in the power-density spectra (PDS) with an evolving QPO frequency ranging from 5.31 ± 0.02 to 7.61 ± 0.09 Hz. We investigate the energy dependence of the QPO and do not find this feature in the PDS above 30 keV. The combined 0.7–80 keV SXT and LAXPC spectra are fitted with a model consisting of thermal multi-colour blackbody emission and Comptonized emission components. We perform time-resolved spectroscopy by extracting spectra during the dip and non-dip phases of the observation. A neutral absorber is detected during the dip and non-dip phases though a signature of an ionized absorber is also present in the dip phases. The spectral and temporal parameters are found to evolve during our observation. We estimate the mass function of the system as f(M) = 2.1–7.2 M_⊙ and the mass of the BH candidate in the range of M_BH ∼ 3.5–12.5 M_⊙.