J/ApJ/956/21 X-ray & opt. light curves of XTE J1859+226 (Bellm+, 2023)
An optically discovered outburst from XTE J1859+226.
Bellm E.C., Wang Y., van Roestel J., Phillipson R.A., Coughlin M.W.,
Tomsick J.A., Groom S.L., Healy B., Purdum J., Rusholme B., Sollerman J.,
Bealo P., Lora S., Muyllaert E., Peretto I., Schwendeman E.J.
<Astrophys. J., 956, 21 (2023)>
=2023ApJ...956...21B 2023ApJ...956...21B
ADC_Keywords: Binaries, X-ray; Photometry, ultraviolet; Optical; Transient
Keywords: Low-mass x-ray binary stars ; X-ray binary stars
Abstract:
Using the Zwicky Transient Facility, in 2021 February we identified
the first known outburst of the black hole X-ray transient
XTE_J1859+226 since its discovery in 1999. The outburst was visible at
X-ray, UV, and optical wavelengths for less than 20 days,
substantially shorter than its full outburst of 320 days in 1999, and
the observed peak luminosity was 2 orders of magnitude lower. Its peak
bolometric luminosity was only 2x1035erg/s, implying an Eddington
fraction of about 3x10-4. The source remained in the hard spectral
state throughout the outburst. From optical spectroscopy measurements
we estimate an outer disk radius of 1011cm. The low observed X-ray
luminosity is not sufficient to irradiate the entire disk, but we
observe a surprising exponential decline in the X-ray light curve.
These observations highlight the potential of optical and infrared
synoptic surveys to discover low-luminosity activity from X-ray
transients.
Description:
The Zwicky Transient Facility (ZTF) uses a large mosaic camera to
survey the Northern Hemisphere sky (δ>-30°) in three optical
bands (g, r, and i) to typical depths of 20.5 mag with a cadence of
two nights or faster.
On 2021 February 4 ZTF observed a field containing XTE J1859+226 five
times in the r band as part of its public twilight survey. We received
a notification from the ANTARES system of a new source, internally
designated ZTF21aagyzqr, coincident with XTE J1859+226.
We triggered Swift target-of-opportunity observations and confirmed
that the X-ray flux had increased by three orders of magnitude
relative to the quiescent level (Bellm 2021ATel14375....1B 2021ATel14375....1B).
We obtained point-spread function forced photometry measurements on
ZTF difference images.
We also obtained difference-image forced photometry from the Asteroid
Terrestrial-impact Last Alert System (ATLAS) forced photometry service.
We imaged XTE J1859+226 in Sloan Digital Sky Survey g, r, and i bands
with the Rainbow Camera of the Spectral Energy Distribution Machine
(SEDM) on the Palomar 60 inch telescope (P60) on 2021 February 8.
We also retrieved the American Association of Variable Star Observers
(AAVSO) photometry from the online download portal.
Along with three-color photometry, on 2021 February 8 we obtained a
low-resolution spectrum of XTE J1859+226 using the P60 SEDM.
We obtained a long-slit spectrum of XTE J1859+226 using the
Low-Resolution Imaging Spectrometer (LRIS) on Keck I on 2021 Feb 15.
We obtained a series of Swift/XRT observations between 2021-Feb-6 and 28.
NuSTAR observed XTE J1859+226 for 40.4ks on 2021 Feb 13. We obtained
publicly available NuSTAR observations (obsid 90701305002, P.I. Harrison)
from the HEASARC.
We also retrieved publicly available daily count rates for XTE_J1859+226
from the Monitor of All-sky X-ray Image (MAXI) and Swift's Burst Alert
Telescope (BAT).
See Section 2.3.
Objects:
----------------------------------------------------------
RA (ICRS) DE Designation(s)
----------------------------------------------------------
18 58 41.49 +22 39 29.7 XTE J1859+226 = ZTF21aagyzqr
----------------------------------------------------------
File Summary:
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FileName Lrecl Records Explanations
--------------------------------------------------------------------------------
ReadMe 80 . This file
fig1a.dat 46 78 UV/Optical outburst lightcurve for XTE J1859+226
fig1b.dat 54 11 X-ray outburst lightcurve for XTE J1859+226
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See also:
B/vsx : AAVSO International Variable Star Index VSX (Watson+, 2006-)
J/A+A/469/807 : Catalogue of Galactic low-mass X-ray binaries (Liu+, 2007)
J/MNRAS/397/1177 : Swift-XRT observations of GRBs (Evans+, 2009)
J/ApJ/699/453 : Determination of black hole masses (Shaposhnikov+, 2009)
J/MNRAS/426/1701 : High-frequency QPO in black hole binaries (Belloni+, 2012)
J/ApJS/209/14 : The Swift/BAT hard X-ray transient monitor (Krimm+, 2013)
J/ApJ/788/48 : X-ray through NIR photometry of NGC 2617 (Shappee+, 2014)
J/BaltA/24/395 : X-ray and radio sources in binaries (Malkov+, 2015)
J/ApJ/800/17 : Mass-transfer sequences in 16 Galactic LMXBs (Fragos+, 2015)
J/other/NewA/47.81 : Distances of X-ray binaries (Islam+, 2016)
J/A+A/593/A68 : PTF12os & iPTF13bvn spectra & light curves (Fremling+, 2016)
J/ApJS/222/15 : WATCHDOG: all-sky database of Gal. BHXBs (Tetarenko+, 2016)
J/A+A/587/A61 : BlackCAT, BH mass in X-ray transient (Corral-Santana+, 2016)
J/A+A/645/A18 : SVOM-ECLAIRs known X-ray sources catalogue (Dagoneau+, 2021)
J/MNRAS/501/2790 : Swift Bulge Survey. first X-ray results (Bahramian+, 2021)
J/ApJ/920/120 : g/r-band observation of AT 2019wey (Yao+, 2021)
J/ApJ/930/20 : Neutron star XRB Centaurus X-4 monitoring (Baglio+, 2022)
J/A+A/675/A199 : XRBcats. Galactic LMXB Catalogue (Avakyan+, 2023)
J/A+A/684/A124 : Galactic LMXBs catalog (Fortin+, 2024)
Byte-by-byte Description of file: fig1a.dat
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Bytes Format Units Label Explanations
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1- 18 F18.12 d MJD [59249.5/59274.6] Time; TDB Modified Julian Date
20- 24 F5.2 mag mag [18.36/21.32]? Apparent AB magnitude in Filt
26- 29 F4.2 mag e_mag [0.03/1.1]? Uncertainty in mag
31- 35 F5.2 mag magLim [18.1/21.4]? The 5-sigma limiting AB magnitude
in Filt
37- 40 A4 --- Filt Bandpass filter name
42- 46 A5 --- Survey Source of data (1)
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Note (1): Survey as follows:
ZTF = the Zwicky Transient Facility (51 occurrences)
AAVSO = the American Association of Variable Star Observers online
download portal (12 occurrences)
UVOT = Swift/UVOT (11 occurrences)
P60 = the Spectral Energy Distribution Machine (SEDM) on the
Palomar 60 inch telescope (4 occurrences)
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Byte-by-byte Description of file: fig1b.dat
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Bytes Format Units Label Explanations
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1- 18 F18.12 d MJD [59252/59273.3] Time; Modified Julian Date
20- 27 E8.2 ct/s Rate [0.006/0.21]? The 0.3-10keV count rate
29- 36 E8.2 ct/s E_Rate [0.003/0.02]? Upper 1-sigma uncertainty in rate
38- 45 E8.2 ct/s e_Rate [0.002/0.02]? Lower 1-sigma uncertainty in rate
47- 54 E8.2 ct/s RateLim [0.013/0.052]? Upper 5-sigma count rate
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History:
From electronic version of the journal
(End) Prepared by [AAS], Emmanuelle Perret [CDS] 05-Dec-2025