A broadband look of the Accreting Millisecond X-ray Pulsar SAX J1748.9-2021 using AstroSat and XMM-Newton

Abstract

SAX J1748.9-2021 is a transient accretion powered millisecond X-ray pulsar located in the Globular cluster NGC 6440. We report on the spectral and timing analysis of SAX J1748.9-2021 performed on AstroSat data taken during its faint and short outburst of 2017. We derived the best-fitting orbital solution for the 2017 outburst and obtained an average local spin frequency of 442.361098(3) Hz. The pulse profile obtained from 3-7 keV and 7-20 keV energy bands suggest constant fractional amplitude ~0.5% for fundamental component, contrary to previously observed energy pulse profile dependence. Our AstroSat observations revealed the source to be in a hard spectral state. The 1-50 keV spectrum from SXT and LAXPC on-board AstroSat can be well described with a single temperature blackbody and thermal Comptonization. Moreover, we found that the combined spectra from XMM-Newton (EPIC-PN) and AstroSat (SXT+LAXPC) indicated the presence of reflection features in the form of iron (Fe K$\alpha$) line that we modeled with the reflection model xillvercp. One of the two X-ray burst observed during the AstroSat/LAXPC observation showed hard X-ray emission (>30 keV) due to Compton up-scattering of thermal photons by the hot corona. Time resolved analysis performed on the bursts revealed complex evolution in emission radius of blackbody for second burst suggestive of mild photospheric radius expansion.

9 pages, 8 figures. Accepted for publication in MNRAS

References in corpus (15)

• An online repository of Swift/XRT light curves of GRBs
• Thermonuclear (type-I) X-ray bursts observed by the Rossi X-ray Timing Explorer
• Near-IR properties of 24 Globular Clusters in the Galactic Bulge
• Broad relativistic iron emission line observed in SAX J1808.4-3658
• Intermittent millisecond X-ray pulsations from the neutron-star X-ray transient SAX J1748.9-2021 in the globular cluster NGC 6440
• XMM-Newton detects a relativistically broadened iron line in the spectrum of the ms X-ray pulsar SAX J1808.4-3658
• The mass and the radius of the neutron star in the transient low mass X-ray binary SAX J1748.9-2021
• AstroSat view of MAXI J1535-571: broadband spectro-temporal features
• Timing an Accreting Millisecond Pulsar: Measuring the Accretion Torque in IGR J00291+5934
• Phase-coherent timing of the accreting millisecond pulsar SAX J1748.9-2021
• Discovery of 442-Hz Pulsations from an X-ray Source in the Globular Cluster NGC 6440
• Truncation of the Accretion Disk at One Third of the Eddington Limit in the Neutron Star Low-Mass X-ray Binary Aquila X-1
• Testing Rate Dependent corrections on timing mode EPIC-pn spectra of the accreting Neutron Star GX 13+1
• Indications of non-conservative mass-transfer in AMXPs
• The Optical Counterpart to the Accreting Millisecond X-ray Pulsar SAX J1748.9-2021 in the Globular Cluster NGC 6440

Cited by in corpus (15)

• Search for continuous gravitational waves from 20 accreting millisecond X-ray pulsars in O3 LIGO data
• Large Area X-ray Proportional Counter (LAXPC) in Orbit Performance : Calibration, background, analysis software
• AstroSat Observations of the first Galactic ULX Pulsar Swift J0243.6+6124
• Thermonuclear X-ray bursts from LMXB 4U 1636$-$536 observed with AstroSat
• Broadband mHz QPOs and spectral study of LMC X$-$4 with AstroSat
• The AstroSat observation of accreting millisecond X-ray pulsar SAX J1808.4-3658 during its 2019 outburst
• Broad-band spectral analysis of LMXB XTE J1710-281 with Suzaku
• AstroSat and NuSTAR observations of XTE J1739-285 during the 2019-2020 outburst
• Eclipse Timings of the LMXB XTE J1710-281 : Discovery of a third orbital period glitch
• Science with the $AstroSat$ Soft X-ray Telescope: an overview
• Sidebands to mHz QPOs in 4U 1626$-$67 in the second spin-down state
• X-ray spectral properties of the accreting millisecond pulsar IGR J17498-2921 during its 2023 outburst
• LAXPC instrument onboard AstroSat: Five exciting years of new scientific results specially on X-ray Binaries
• Change in spin-down rate and detection of emission line in HMXB 4U 2206+54 with AstroSat observation
• AstroSat observation of the magnetar SGR J1830$-$0645 during its first detected X-ray outburst