J/ApJS/280/49 20yr phot. observations of the SMC with OGLE (Mroz+, 2025)
Microlensing optical depth, event rate, and limits on compact objects in dark
matter based on 20yr of OGLE observations of the Small Magellanic Cloud.
Mroz P., Udalski A., Szymanski M.K., Soszynski I., Pietrukowicz P.,
Kozlowski S., Poleski R., Skowron J., Skowron D., Ulaczyk K.,
Gromadzki M., Rybicki K., Iwanek P., Wrona M., Ratajczak M.
<Astrophys. J. Suppl. Ser., 280, 49 (2025)>
=2025ApJS..280...49M 2025ApJS..280...49M
ADC_Keywords: Gravitational lensing; Photometry, RI
Keywords: Gravitational microlensing ; Dark matter ;
Milky Way dark matter halo ; Small Magellanic Cloud ;
Primordial black holes ; Intermediate-mass black holes
Abstract:
Some previous studies have suggested that massive and
intermediate-mass primordial black holes (PBHs) could comprise a
substantial fraction of dark matter in the Universe. Such black holes,
if they existed in the Milky Way halo, would give rise to
long-duration microlensing events that may potentially last for years.
However, earlier searches were not sufficiently sensitive to detect
such events. Here, we present the results of searches for
long-timescale gravitational microlensing events toward the Small
Magellanic Cloud (SMC) using nearly 20yr of photometric observations
collected by the Optical Gravitational Lensing Experiment (OGLE) from
2001-2020. We found six events, three of which are new discoveries. We
use a sample of five events to measure the microlensing optical depth
toward the SMC τ=(0.32±0.18)x10-7 and the event rate
Γ=(1.18±0.57)x10-7/yr/star. The properties of the detected
events are consistent with lenses originating from known stellar
populations within the SMC or in the Milky Way disk. No events with
timescales longer than 1yr were detected, which provides competitive
limits on the fraction of massive compact objects, including PBHs, in
the Milky Way dark matter halo. Together with the earlier OGLE studies
of microlensing events in the direction of the Large Magellanic Cloud,
these observations rule out PBHs and other compact objects with masses
ranging from 10-8-103M☉ as dominant components of dark
matter.
Description:
The photometric data that are analyzed in this paper were collected
during the fourth phase of the OGLE survey (OGLE-IV;
Udalski+ 2015AcA....65....1U 2015AcA....65....1U) between 2010 June 29 (JD=2,455,377) and
2020 March 15 (JD=2,458,924). The survey uses a dedicated 1.3m Warsaw
Telescope located at Las Campanas Observatory, Chile.
The OGLE-IV project observes an area of approximately 190deg2
surrounding the SMC. This region is divided into 135 fields, whose
locations are shown in Figure 1 (see Table 1).
Most of the data were taken in the I-band filter, whose transmission
curve closely resembles that of the standard Cousins photometric
system. The number of I-band epochs varies from 151 to 1090, with a
median count of 376. In addition, a smaller number of images were
taken through the V-band filter (from 7 to 321 per field with a median
of 22). Fields covering the SMC center were observed at a 2-5 day
cadence, whereas the outer fields were observed less frequently,
typically every 4-6 days. Exposure times varied between 150 and 170s.
Because our main scientific goal was to search for long-duration
microlensing events, we supplemented the OGLE-IV light curves with
data collected during the third phase of the survey (OGLE-III;
Udalski 2003AcA....53..291U 2003AcA....53..291U), following the methodology detailed in
Paper I (Mroz+ 2024ApJS..273....4M 2024ApJS..273....4M). The OGLE-III data were gathered
from 2001 June 24 (JD=2,452,085) to 2009 May 2 (JD=2,454,954). This
approach allowed us to extend the OGLE-IV light curves to nearly 20yr.
File Summary:
--------------------------------------------------------------------------------
FileName Lrecl Records Explanations
--------------------------------------------------------------------------------
ReadMe 80 . This file
table1.dat 66 135 OGLE-IV fields toward the Small Magellanic Cloud
table2.dat 35 4320 Error bar correction coefficients for the I-band
data
table4.dat 108 6 Detected microlensing events
table6.dat 69 4320 *Number of microlensing source stars observed in
OGLE-IV fields
phot/* . 6 Calibrated I-band photometry of individual events
--------------------------------------------------------------------------------
Note on table6.dat: The total values for each column, in the same data format,
but where the number of sources are in the millions:
--------------------------------------------------------------
N21Tot N21Corr N21.5Tot N21.5Corr N22Tot N22Corr
--------------------------------------------------------------
Total 9.606 6.316 13.364 9.689 16.230 12.351
--------------------------------------------------------------
--------------------------------------------------------------------------------
See also:
I/355 : Gaia DR3 Part 1. Main source (Gaia Collaboration, 2022)
J/AcA/50/421 : OGLE-II DIA BUL_SC1 field (Wozniak, 2000)
J/A+A/529/A102 : MOA-2007-BLG-387Lb light curve I band (Batista+, 2011)
J/AJ/144/4 : Dwarf galaxies in the Local Group (McConnachie+, 2012)
J/A+A/616/A12 : Gaia DR2 sources in GC and dSph (Gaia Collaboration+, 2018)
J/ApJS/244/29 : Microlensing events toward the Galactic bulge (Mroz+, 2019)
J/ApJ/904/13 : Radial velocity for 10 giant EBs (Graczyk+, 2020)
J/A+A/649/A7 : MC structure and properties (Gaia Collaboration+, 2021)
J/ApJS/252/23 : Reddening map of MCs from OGLE-IV RC stars (Skowron+, 2021)
https://www.astrouw.edu.pl/ogle/ogle4/SMC_OPTICAL_DEPTH/ : associated data of
this paper (also doi:10.5281/zenodo.16735482)
Byte-by-byte Description of file: table1.dat
--------------------------------------------------------------------------------
Bytes Format Units Label Explanations
--------------------------------------------------------------------------------
1- 6 A6 --- Field OGLE-IV field name (SMCNNN)
8- 9 I2 h RAh Hour of Right ascension (J2000)
11- 12 I2 min RAm Minute of Right ascension (J2000)
14- 15 I2 s RAs Second of Right ascension (J2000)
17 A1 --- DE- Sign of the Declination (J2000)
18- 19 I2 deg DEd Degree of Declination (J2000)
21- 22 I2 arcmin DEm Arcminute of Declination (J2000)
24- 25 I2 arcsec DEs Arcsecond of Declination (J2000)
27- 30 I4 --- Nepoch1 [0/702] Minimal number of OGLE-III epochs in
I band; 2001-2009
32- 35 I4 --- Nepoch2 [0/3318] Maximal number of OGLE-III epochs in
V band; 2001-2009
37- 40 I4 --- Nepoch3 [151/1090] Number of OGLE-IV epochs in I
band; 2010-2020
42- 45 I4 --- Nepoch4 [7/321] Number of OGLE-IV epochs in V band;
2010-2020
47- 52 F6.1 --- Nstars1 [0/1463.1] Number of stars observed during
both OGLE-III and OGLE-IV; in thousands
54- 59 F6.1 --- Nstars2 [0/137.9] Number of stars observed during
OGLE-IV only; in thousands
61- 66 F6.1 --- Nstars3 [21.3/1473] Total number of stars; in thousands
--------------------------------------------------------------------------------
Byte-by-byte Description of file: table2.dat
--------------------------------------------------------------------------------
Bytes Format Units Label Explanations
--------------------------------------------------------------------------------
1- 6 A6 --- Field OGLE-IV field name (SMCNNN)
7 A1 --- --- [.]
8- 9 I02 --- sField OGLE-IV subfield name (NN;
SMCNNN.NN for a complete designation)
11- 15 F5.3 --- gam3 [0.9/1.96]? Gamma coefficient for OGLE-III data
17- 22 F6.4 --- eps3 [0.005/0.021]? Epsilon coefficient for OGLE-III
data
24- 28 F5.3 --- gam4 [0.8/2.21] Gamma coefficient for OGLE-IV data
30- 35 F6.4 --- eps4 [0.002/0.15] Epsilon coefficient for OGLE-IV data
--------------------------------------------------------------------------------
Byte-by-byte Description of file: table4.dat
--------------------------------------------------------------------------------
Bytes Format Units Label Explanations
--------------------------------------------------------------------------------
1- 11 A11 --- Event Microlensing event name
13- 14 I2 h RAh [0/1] Hour of right ascension (J2000)
16- 17 I2 min RAm Minute of right ascension (J2000)
19- 23 F5.2 s RAs Second of right ascension (J2000)
25 A1 --- DE- [-] Sign of declination (J2000)
26- 27 I2 deg DEd [72/73] Degree of declination (J2000)
29- 30 I2 arcmin DEm Arcminute of declination (J2000)
32- 35 F4.1 arcsec DEs Arcsecond of declination (J2000)
37- 65 A29 --- OGLEIV OGLE-IV identifier(s)
67- 72 F6.3 mag Imag [18.2/20.65] I band magnitude
74- 78 F5.3 mag e_Imag [0.01/0.012] Uncertainty on the Imag
80- 84 F5.3 mag V-I [0.001/1.16] V-I color index
86- 90 F5.3 mag e_V-I [0.014/0.017] V-I uncertainty
92- 96 F5.3 --- E(V-I) [0.03/0.12] V-I color excess
98- 102 F5.3 --- e_E(V-I) [0.029/0.071] Lower uncertainty on E(V-I)
104- 108 F5.3 --- E_E(V-I) [0.026/0.065] Upper uncertainty on E(V-I)
--------------------------------------------------------------------------------
Byte-by-byte Description of file: table6.dat
--------------------------------------------------------------------------------
Bytes Format Units Label Explanations
--------------------------------------------------------------------------------
1- 6 A6 --- Field OGLE-IV field name (SMCNNN)
7 A1 --- --- [.]
8- 9 I02 --- sField OGLE-IV subfield name (NN;
SMCNNN.NN for a complete designation)
11- 18 F8.4 deg RAdeg Right ascention (J2000)
20- 27 F8.4 deg DEdeg [-83/-62.7] Declination (J2000)
29- 34 I6 --- N21Tot [398/174447] Total number of sources
brighter than I=21 mag
36- 41 I6 --- N21Corr [0/173678] Corrected number of sources
brighter than I=21 mag
43- 48 I6 --- N21.5Tot [434/244105] Number of sources brighter than
I=21.5 mag
50- 55 I6 --- N21.5Corr [0/243240] Corrected number of sources
brighter than I=21.5 mag
57- 62 I6 --- N22Tot [481/338613] Total number of sources
brighter than I=22 mag
64- 69 I6 --- N22Corr [0/337698] Corrected number of sources
brighter than I=22 mag
--------------------------------------------------------------------------------
Byte-by-byte Description of file: phot/*
--------------------------------------------------------------------------------
Bytes Format Units Label Explanations
--------------------------------------------------------------------------------
1- 13 F13.5 d HJD Heliocentric Julian Date
15- 20 F6.3 mag Imag I magnitude
22- 26 F5.3 mag e_Imag Magnitude error
--------------------------------------------------------------------------------
History:
From electronic version of the journal
Photometry downloaded at:
https://www.astrouw.edu.pl/ogle/ogle4/SMC_OPTICAL_DEPTH/
(also doi:10.5281/zenodo.16735482)
License: CC-BY-4.0
References:
Mroz et al. Paper I. 2024ApJS..273....4M 2024ApJS..273....4M
Mroz et al. Paper II. 2024Natur.632..749M 2024Natur.632..749M
Mroz et al. Paper III. 2024ApJ...976L..19M 2024ApJ...976L..19M
(End) Prepared by [AAS], Emmanuelle Perret [CDS] 04-Jun-2026