J/ApJ/917/69 SOAR opt. phot. & sp. in 4FGLJ0540.0-7552 field (Strader+, 2021)
Multiwavelength evidence for a new flare-mode transitional millisecond pulsar.
Strader J., Swihart S.J., Urquhart R., Chomiuk L., Aydi E., Bahramian A.,
Kawash A., Sokolovsky K.V., Tremou E., Udalski A.
<Astrophys. J., 917, 69 (2021)>
=2021ApJ...917...69S 2021ApJ...917...69S
ADC_Keywords: Pulsars; Gamma rays; Binaries, X-ray; Spectra, optical; Photometry
Keywords: Millisecond pulsars
Abstract:
We report the discovery of a new low-mass X-ray binary near the center
of the unassociated Fermi GeV γ-ray source 4FGL J0540.0-7552.
The source shows the persistent presence of an optical accretion disk
and exhibits extreme X-ray and optical variability. It also has an
X-ray spectrum well-fit by a hard power law with Γ=1.8 and a
high ratio of X-ray to γ-ray flux. Together, these properties
are consistent with the classification of the binary as a transitional
millisecond pulsar (tMSP) in the subluminous disk state. Uniquely
among the candidate tMSPs, 4FGL J0540.0-7552 shows consistent optical,
X-ray, and γ-ray evidence for having undergone a state change,
becoming substantially brighter in the optical and X-rays and fainter
in GeV γ-rays sometime in mid-2013. In its current subluminous
disk state, and like one other candidate tMSP in the Galactic field,
4FGL J0540.0-7552 appears to always be in an X-ray "flare mode",
indicating that this could be common phenomenology for tMSPs.
Description:
After its appearance in the 2FGL catalog, the region containing
4FGLJ0540.0-7552 was imaged with Swift/XRT on three epochs from
2012-January to May, for about 4.5ks of total exposure time, as part
of an ongoing program to image unassociated Fermi sources
(Stroh & Falcone 2013ApJS..207...28S 2013ApJS..207...28S).
Owing to its location near the south ecliptic pole, this region had
relatively deep ROSAT X-ray imaging from 1990 to 1991, totaling 5.1ks
with the Position Sensitive Proportional Counter instrument.
On 2021 January 23, we used XMM-Newton with the European Photon
Imaging Camera (EPIC) to observe the region centered on
4FGLJ0540.0-7552, with an on-source live exposure time of 41.8ks.
The field containing J0540A (Gaia DR3 4648562268335471104) and J0540B
(Gaia DR3 4648562676357022208) was observed in the I filter during a
subset of operations of the OGLE survey of the Magellanic Clouds,
though J0540B is relatively faint. We use the photometry for J0540B,
retaining all 5σ detections from the time range in which the
field was regularly observed (late 2012 to early 2015).
For J0540A, the OGLE data are relatively sparse, so we instead use
data from the ASAS-SN survey. Focusing just on the more abundant g
filter, there are over 4700 clean ASAS-SN detections of the source
from 2017 October to 2021 April.
We obtained additional photometry of J0540B with the Goodman
Spectrograph on the SOAR telescope on 2021 January 13 and 19.
See Section 2.3.1.
We obtained 14 optical spectra of J0540A with the Goodman Spectrograph
on the SOAR telescope on several nights over the date range
2016 September 19 to 2016 December 31.
We obtained 10 optical spectra of J0540B with SOAR/Goodman on
2020 December 20 and 2021 January 9. Each of the spectra had the same
exposure time (25min) and covered the same wavelength range
(∼3950-7850Å) at a resolution of 5.6Å. Subsequently, we obtained
six spectra on the nights of 2021 February 4, 5, and 6 with GMOS-S on
the Gemini South telescope under program code GS-2021A-FT-101. Each of
these Gemini spectra were 20min in length, and covered a wavelength
range ∼4600-9150Å at a resolution of 7.1Å.
See Section 2.4.
While no new radio continuum data are presented in this paper, the
region around 4FGL J0540.0-7552 was imaged by the Australia Telescope
Compact Array in 2013 and 2014. No radio continuum source within the
Fermi-LAT error ellipse of this source was detected, down to a limit
of ≲1.5mJy (Schinzel+ 2017, J/ApJ/838/139).
Objects:
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RA (ICRS) DE Designation(s)
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05 40 01.85 -75 54 19.4 J0540B = Gaia DR3 4648562676357022208
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File Summary:
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FileName Lrecl Records Explanations
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ReadMe 80 . This file
table1.dat 26 1010 SOAR/Goodman photometry of J0540B
(Gaia DR3 4648562676357022208)
sp/* . 1 *25-min SOAR/Goodman spectrum of J0540B from
2020 Dec 20 as shown in Figure 6 in FITS format
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Note on sp/*: The spectrum has a FWHM resolution of 5.6 Angstroms.
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See also:
B/swift : Swift Master Catalog (HEASARC, 2004-)
B/xmm : XMM-Newton Obs. Log (XMM-Newton Science Operation Center, 2012)
I/352 : Distances to 1.47 billion stars in Gaia EDR3 (Bailer-Jones+, 2021)
I/355 : Gaia DR3 Part 1. Main source (Gaia Collaboration, 2022)
J/MNRAS/360/974 : Proper motions of pulsars (Hobbs+, 2005)
J/ApJS/199/31 : Fermi LAT second source catalog (2FGL) (Nolan+, 2012)
J/ApJS/208/17 : 2nd Fermi LAT cat. of gamma-ray pulsars (2PC) (Abdo+, 2013)
J/ApJ/788/48 : X-ray through NIR photometry of NGC 2617 (Shappee+, 2014)
J/A+A/588/A103 : 2nd ROSAT all-sky survey (2RXS) sources (Boller+, 2016)
J/MNRAS/458/3341 : 42 ms pulsars high-precision timing (Desvignes+, 2016)
J/ApJ/831/89 : Eclipsing LMXB in 3FGL J0427.9-6704 (Strader+, 2016)
J/ApJ/838/139 : Radio obs. of 3FGL unassociated sources (Schinzel+, 2017)
J/ApJS/237/28 : WISE catalog of periodic variable stars (Chen+, 2018)
J/ApJ/866/83 : Opt/NIR obs. of 1FGLJ1417.7-4407 (Swihart+, 2018)
J/ApJ/872/42 : Opt. sp. of redback ms pulsar binaries (Strader+, 2019)
J/ApJS/247/33 : Fermi LAT fourth source catalog (4FGL) (Abdollahi+, 2020)
J/ApJ/901/57 : MAVERIC survey: X-ray sources in GCs (Bahramian+, 2020)
J/ApJ/904/49 : 4FGLJ0407.7-5702 opt. sp. & light curve (Miller+, 2020)
J/MNRAS/501/1116 : GAIA pulsars and where to find them (Antoniadis, 2021)
Byte-by-byte Description of file: table1.dat
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Bytes Format Units Label Explanations
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1- 13 F13.7 d BMJD [59227/59233.3] Barycentric Modified Julian Date
(BJD-2400000.5) on the TDB system
(Eastman+ 2010PASP..122..935E 2010PASP..122..935E)
15- 20 F6.3 mag Gmag [19.29/21.11] SOAR/Goodman G band (calibrated to
Gaia G) magnitude
22- 26 F5.3 mag e_Gmag [0.007/0.04] Uncertainty in Gmag
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History:
From electronic version of the journal
(End) Prepared by [AAS], Emmanuelle Perret [CDS] 11-Jan-2023