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Most dynamically confirmed stellar-mass black holes and the candidates were originally selected from X-ray outbursts. In the present work, we search for black hole candidates in the LAMOST survey by using the spectra along with photometry from the ASAS-SN survey, where the orbital period of the binary may be revealed by the periodic light curve, such as the ellipsoidal modulation type. Our sample consists of 9 binaries, where each source contains a giant star with large radial velocity variation ($Delta V_{rm R} > 70~{rm km~s^{-1}}$) and periods known from light curves. We focus on the 9 sources with long periods ($T_{rm ph} > 5$ days) and evaluate the mass $M_2$ of the optically invisible companion. Since the observed $Delta V_{rm R}$ from only a few repeating spectroscopic observations is a lower limit of the real amplitude, the real mass $M_2$ can be significantly higher than the current evaluation. It is likely an efficient method to place constraints on $M_2$ by combining $Delta V_{rm R}$ from LAMOST and $T_{rm ph}$ from ASAS-SN, particularly by the ongoing LAMOST Medium Resolution Survey.
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We propose a method to search for stellar-mass black hole (BH) candidates with giant companions from spectroscopic observations. Based on the stellar spectra of LAMOST Data Release 6, we obtain a sample of seven giants in binaries with large radial velocity variation $Delta V_R > 80~{rm km~s^{-1}}$. With the effective temperature, surface gravity, and metallicity provided by LAMOST, and the parallax given by {it Gaia}, we can estimate the mass and radius of the giant, and therefore evaluate the possible mass of the optically invisible star in the binary. We show that the sources in our sample are potential BH candidates, and are worthy of dynamical measurement by further spectroscopic observations. Our method may be particularly valid for the selection of BH candidates in binaries with unknown orbital periods.
We study the prospects of searching for black hole (BH) binary systems with a stellar-mass BH and a non-compact visible companion, by utilizing the spectroscopic data of Large Sky Area Multi-Object Fiber Spectroscopic Telescope (LAMOST). We simulate the Galactic BH binary population and determine its optical visibility by considering the stellar synthetic population model and the distributions of binary orbital parameters. By convolving the visibility of BH binaries with the LAMOST detection sensitivity, we predict that $gtrsim$ 400 candidate BH binaries can be found by the low-resolution, non-time-domain survey, and $sim$ 50-350 candidates by the LAMOST ongoing medium-resolution, time-domain spectroscopic survey. Most of the candidates are short-period (0.2-2 days) binaries with M-, K-, G-, or F-type companions, in which $sim$ 47% have a mass function (the lower limit of the BH mass) larger than 3 $M_{odot}$. By complementing the LAMOST spectroscopic data with other photometric/spectroscopic surveys or follow-up observations, these candidates could be confirmed. Therefore, by exploring the LAMOST data, we can enlarge the sample of dynamically confirmed BH binaries significantly, which can improve our understanding of the mass distribution of BHs and the stellar evolution model.
We present Citizen ASAS-SN, a citizen science project hosted on the Zooniverse platform which utilizes data from the All-Sky Automated Survey for SuperNovae (ASAS-SN). Volunteers are presented with ASAS-SN $g$-band light curves of variable star candidates. The classification workflow allows volunteers to classify these sources into major variable groups, while also allowing for the identification of unique variable stars for additional follow-up.
Graham et al. (2015a) reported a periodically varying quasar and supermassive black hole binary candidate, PG1302-102 (hereafter PG1302), which was discovered in the Catalina Real-Time Transient Survey (CRTS). Its combined Lincoln Near-Earth Asteroid Research (LINEAR) and CRTS optical light curve is well fitted to a sinusoid of an observed period of $approx 1,884$ days and well modeled by the relativistic Doppler boosting of the secondary mini-disk (DOrazio et al. 2015). However, the LINEAR+CRTS light curve from MJD $approx 52700$ to MJD $approx 56400$ covers only $sim 2$ cycles of periodic variation, which is a short baseline that can be highly susceptible to normal, stochastic quasar variability (Vaughan et al. 2016). In this Letter, we present a re-analysis of PG1302, using the latest light curve from the All-Sky Automated Survey for Supernovae (ASAS-SN), which extends the observational baseline to the present day (MJD $approx 58200$), and adopting a maximum likelihood method which searches for a periodic component in addition to stochastic quasar variability. When the ASAS-SN data are combined with the previous LINEAR+CRTS data, the evidence for periodicity decreases. For genuine periodicity one would expect that additional data would strengthen the evidence, so the decrease in significance may be an indication that the binary model is disfavored.
The ultralight boson is a promising candidate for dark matter. These bosons may form long-lived bosonic clouds surrounding rotating black holes via superradiance, acting as sources of gravity and affecting the propagation of gravitational waves around the host black hole. If the mass ratio of a compact merger is sufficiently small, the bosonic cloud will survive the inspiral phase of a binary merger and can affect the quasinormal-mode frequencies of the perturbed black hole and bosonic cloud system. In this work, we compute the shift of gravitational QNMFs of a rotating black hole due to the presence of a surrounding bosonic cloud. We then perform a mock analysis on simulated LISA observational data containing injected ringdown signals from supermassive black holes with and without a bosonic cloud. We find that with less than an hour of observational data of the ringdown phase of nearby supermassive black holes such as Sagittarius A* and M32, we can rule out or confirm the existence of cloud-forming ultralight bosons of mass $ sim 10^{-17} rm eV$.
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