J/ApJS/269/28 Microlensing event rate in the GC. I. UKIRT obs. (Wen+, 2023)
Toward measuring the microlensing event rate in the Galactic center.
I. Event detection from the UKIRT microlensing survey data.
Wen Y., Zang W., Ma Bo
<Astrophys. J. Suppl. Ser., 269, 28 (2023)>
=2023ApJS..269...28W 2023ApJS..269...28W
ADC_Keywords: Gravitational lensing; Infrared sources; Surveys;
Cross identifications; Galactic center
Keywords: Gravitational microlensing exoplanet detection ;
Exoplanet astronomy ; Near infrared astronomy ; Surveys ; Catalogs
Abstract:
To overcome the high optical extinction, near-infrared (NIR)
observations are needed for probing the microlensing events toward the
Galactic center. The 2015-2019 UKIRT microlensing survey toward the
Galactic center is the first dedicated precursor NIR survey for the
Nancy Grace Roman Space Telescope. Here, we analyze the online data
from the UKIRT microlensing survey, reaching l=b=0°. Using the
event-finder algorithm of KMTNet with the Δχ2 threshold of
250, we find 522 clear events, 436 possible events, and 27 possible
anomalous events. We fit a point-source point-lens (PSPL) model to all
the clear events and derive the PSPL parameters with uncertainties
using a Markov Chain Monte Carlo method. Assuming perfect detection
efficiency, we compute the uncorrected event rates, which should serve
as the lower limits on the true event rate. We find that the
uncorrected NIR event rates are likely rising toward the Galactic
center and are higher than the optical event rates.
Description:
The UKIRT microlensing survey data were taken using the Wide Field
Camera with a pixel scale of 0.4" and a field of view of about
0.8deg2. The UKIRT microlensing survey fields from 2015-2019 are
summarized in Figure 1.
In total, the five-year-long survey produced 100.5 million light
curves for ∼66 million targets (UKIRT Microlensing Team 2019,
doi: 10.26133/NEA7), with each target yielding one light curve during
annual observations. We download all the light-curve products from the
UKIRT Microlensing Survey website. The majority of the survey targets
have magnitudes brighter than 18 in both the H and K band, with the
photometric precision of 0.01-0.1mag.
See Section 2.
During 2015-2019, the OGLE-IV and MOA-II surveys conducted the bulge
surveys, and since 2016 the KMTNet survey has been conducting its
regular bulge survey. To double check our microlensing event search,
we crossmatch our UKIRT events with the OGLE, MOA-II, and KMTNet
events. Here we only check 2017-2019 events.
See Section 4.
File Summary:
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FileName Lrecl Records Explanations
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ReadMe 80 . This file
table5.dat 75 1663 Summary of microlensing events with observations
from UKIRT and at least one other microlensing
survey (OGLE, MOA, or KMTNet)
tablea1.dat 111 522 Parameters of the clear point source point lens
microlensing events from the UKIRT survey
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See also:
J/other/Nat/481.167 : 2002-2007 PLANET microlensing events (Assan+, 2012)
J/ApJ/778/150 : Microlensing events toward the Bulge (Sumi+, 2013)
J/MNRAS/457/4089 : Frequency of snowline-region planets (Shvartzvald+, 2016)
J/ApJ/827/139 : Microlensing opt. depths from MOA-II (Sumi+, 2016)
J/AJ/154/210 : 2015 high-cadence Spitzer microlensing events (Zhu+, 2017)
J/AJ/155/186 : The KMTNet/K2-C9 (Kepler) Data Release (Kim+, 2018)
J/ApJS/244/29 : Microlensing events toward the Galactic bulge (Mroz+, 2019)
J/ApJ/889/56 : VVV survey microlensing events (Navarro+, 2020)
J/AJ/161/126 : I-band LC of KMT-2017-BLG-2820 (Ryu+, 2021)
J/AJ/162/163 : Systematic KMTNet Planetary Anomaly Search. I. (Zang+, 2021)
http://kmtnet.kasi.re.kr/~ulens/ : KMTNet microlensing events archive
http://ogle.astrouw.edu.pl/ogle4/ews/ews.html : OGLE-IV EWS archive
http://www.massey.ac.nz/~iabond/moa/alerts/ : MOA Transient alerts archive
http://exoplanetarchive.ipac.caltech.edu/docs/UKIRTMission.html : UKIRT home
Byte-by-byte Description of file: table5.dat
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Bytes Format Units Label Explanations
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1- 27 A27 --- ID Source ID in the UKIRT database
(ukirtc2015aNNNNNNNNNN) (1)
29- 38 F10.6 deg RAdeg [263/272] Right Ascension (J2000)
40- 49 F10.6 deg DEdeg [-31/-26] Declination (J2000)
51- 52 A2 --- --- [KB]
53- 58 I06 --- KB ? Events names of KMTNet if available
(KMT-20YY-BLG-NNNN;
see also Kim+ 2018, J/AJ/155/186)
60- 61 A2 --- --- [MB]
62- 66 I05 --- MB ? Events names of MOA if available
(MOA-20YY-BLG-NNN)
68- 69 A2 --- --- [OB]
70- 75 I06 --- OB ? Events names of OGLE if available
(<OGLE-20YY-BLG-NNNN> in Simbad)
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Note (1): Each UKIRT light curve source ID follows the same format:
"ukirt_" + "c" (Photometry Method) + "YYYY" (survey year) +
"a" (Galactic Bulge Region) + "FF" (field ID) + "N_" (CCD ID) +
NNNNNNN (Index)
Photometry Method: the "c" identifies that this specific photometry product
was produced by the CASU pipeline
Galactic Bulge Region with a letter as:
"c" = the central Galactic bulge fields from the 2017-2019 UKIRT
microlensing surveys;
"n" = the northern Galactic bulge fields
"s" = the southern Galactic bulge fields
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Byte-by-byte Description of file: tablea1.dat
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Bytes Format Units Label Explanations
--------------------------------------------------------------------------------
1- 5 A5 --- --- [UKIRT]
6- 8 I03 --- Seq [1/522] UKIRT running sequence number identifier
10- 19 F10.6 deg RAdeg [263/272] Right Ascension (J2000)
21- 30 F10.6 deg DEdeg [-31/-26] Declination (J2000)
32- 36 F5.3 --- u0 [0/1.5] Impact parameter
38- 42 F5.3 --- E_u0 [0/1] Upper uncertainty in u0
44- 48 F5.3 --- e_u0 [0/0.6] Lower uncertainty in u0
50- 57 F8.3 d t0 [7182/8731] Julian Date peak magnification;
JD-24540000.0
59- 63 F5.3 d E_t0 [0.003/7] Upper uncertainty in t0
65- 69 F5.3 d e_t0 [0.003/9] Lower uncertainty in t0
71- 77 F7.3 d tE [1.6/348] Einstein radius crossing time
79- 85 F7.3 d E_tE [0.07/153] Upper uncertainty in tE
87- 93 F7.3 d e_tE [0.05/259] Lower uncertainty in tE
95- 99 F5.3 --- fbl [0.001/1] Blending parameter (1=no blending;
∼0=extreme blending) (1)
101-105 F5.3 --- E_fbl [0/0.8] Upper uncertainty in fbl
107-111 F5.3 --- e_fbl [0/0.3] Lower uncertainty in fbl
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Note (1): We introduce the blending parameter, fbl, for the strength of
the blending, and:
fbl=FS/(FS+FB)
Where FS and FB represent the source flux and any blended flux,
respectively. See Section 3.1; Equation 7.
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History:
From electronic version of the journal
(End) Prepared by [AAS], Emmanuelle Perret [CDS] 02-Feb-2024