J/MNRAS/453/1562 CRTS close supermassive black hole binaries (Graham+, 2015)
A systematic search for close supermassive black hole binaries in the
Catalina Real-time Transient Survey.
Graham M.J., Djorgovski S.G., Stern D., Drake A.J., Mahabal A.A.,
Donalek C., Glikman E., Larson S., Christensen E.
<Mon. Not. R. Astron. Soc., 453, 1562-1576 (2015)>
=2015MNRAS.453.1562G 2015MNRAS.453.1562G (SIMBAD/NED BibCode)
ADC_Keywords: QSOs ; Stars, masses
Keywords: methods: data analysis - techniques: photometric - surveys -
quasars: general - quasars: supermassive black holes
Abstract:
Hierarchical assembly models predict a population of supermassive
black hole (SMBH) binaries. These are not resolvable by direct imaging
but may be detectable via periodic variability (or nanohertz frequency
gravitational waves). Following our detection of a 5.2-year periodic
signal in the quasar PG 1302-102, we present a novel analysis of the
optical variability of 243 500 known spectroscopically confirmed
quasars using data from the Catalina Real-time Transient Survey (CRTS)
to look for close (<0.1pc) SMBH systems. Looking for a strong
Keplerian periodic signal with at least 1.5 cycles over a baseline of
nine years, we find a sample of 111 candidate objects. This is in
conservative agreement with theoretical predictions from models of
binary SMBH populations. Simulated data sets, assuming stochastic
variability, also produce no equivalent candidates implying a low
likelihood of spurious detections. The periodicity seen is likely
attributable to either jet precession, warped accretion discs or
periodic accretion associated with a close SMBH binary system. We also
consider how other SMBH binary candidates in the literature appear in
CRTS data and show that none of these are equivalent to the identified
objects. Finally, the distribution of objects found is consistent with
that expected from a gravitational-wave-driven population. This
implies that circumbinary gas is present at small orbital radii and is
being perturbed by the black holes. None of the sources is expected to
merge within at least the next century. This study opens a new unique
window to study a population of close SMBH binaries that must exist
according to our current understanding of galaxy and SMBH evolution.
Description:
CRTS leverages the Catalina Sky Survey data streams from three
telescopes - the 0.7m Catalina Sky Survey Schmidt and 1.5m Mount
Lemmon Survey telescopes in Arizona, and the 0.5m Siding Springs
Survey Schmidt in Australia - used in a search for Near-Earth
Objects, operated by Lunar and Planetary Laboratory at University of
Arizona. CRTS covers up to ∼2500deg2 per night, with four exposures
per visit, separated by 10-min, over 21 nights per lunation. All data
are automatically processed in real-time, and optical transients are
immediately distributed using a variety of electronic mechanisms. The
data are broadly calibrated to Johnson V (see Drake et al., 2013,
Cat. J/ApJ/763/32 for details) and the full CRTS data set contains
time series for approximately 500 million sources.
The Million Quasars (MQ) catalogue v3.7 contains all spectroscopically
confirmed type 1 QSOs (309525), AGN (21728) and BL Lacs (1573) in the
literature up to 2013 November 26 and formed the basis for the results
of Graham et al. (2015Natur.518...74G 2015Natur.518...74G). We have extended this with
297301 spectroscopically identified quasars in the SDSS Data Release
12 (Paris et al., in preparation). We cross-matched this combined
quasar list against the CRTS data set with a 3-arcsec matching radius
and find that 334446 confirmed quasars are covered by the full CRTS.
Our final sample consists of 111 quasars.
File Summary:
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FileName Lrecl Records Explanations
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ReadMe 80 . This file
table2.dat 110 111 The 111 periodic quasar candidates meeting the
selection criteria
images/* . 12 PNG files with light curves
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Byte-by-byte Description of file: table2.dat
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Bytes Format Units Label Explanations
--------------------------------------------------------------------------------
1- 24 A24 --- Name Name
27- 28 I2 h RAh Rigth ascension (J2000)
30- 31 I2 min RAm Rigth ascension (J2000)
33- 37 F5.2 s RAs Rigth ascension (J2000)
38 A1 --- DE- Declination sign (J2000)
39- 40 I2 deg DEd Declination (J2000)
42- 43 I2 arcmin DEm Declination (J2000)
45- 48 F4.1 arcsec DEs Declination (J2000)
50- 54 F5.3 --- z Redshift
56- 60 F5.2 mag Vmed Median V magnitude
62- 65 I4 d Per Period
67- 71 F5.2 [Msun] logMBH ?=0 Black hole mass (1)
73- 77 F5.3 pc r ?=0 Separation (2)
79- 85 E7.2 yr tinsp ?=0 Rest-frame merger time (2)
87- 91 F5.2 ns DtGW ?=0 Maximum induced timing residual amplitude (2)
92-110 A19 --- LC Name of the file with light curve in
subdirectory images
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Note (1): From Shen et al. (2008, Cat. J/ApJ/680/169) and updates or directly
from spectra where a value is not available.
Note (2): Binary system parameters. All assume q=0.5.
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History:
From electronic version of the journal
(End) Patricia Vannier [CDS] 16-Feb-2016