Evidence of intra-binary shock emission from the redback pulsar PSR J1048+2339^⋆

¹ Università dell’Insubria, Dipartimento di Scienza e Alta Tecnologia, Via Valleggio 11, 22100 Como, Italy
² INAF, Osservatorio Astronomico di Brera, Via E. Bianchi 46, 23807 Merate, LC, Italy
e-mail: arianna.miraval@inaf.it
³ INAF, Osservatorio Astronomico di Cagliari, Via della Scienza 5, 09047 Selargius, CA, Italy
⁴ Max-Planck-Institut für Radioastronomie, Auf dem Hügel 69, 53121 Bonn, Germany
⁵ Institute of Space Sciences (ICE, CSIC), Campus UAB, Carrer de Can Magrans s/n, 08193 Barcelona, Spain
⁶ Institut d’Estudis Espacials de Catalunya (IEEC), Carrer Gran Capità 2–4, 08034 Barcelona, Spain
⁷ ASTRON, The Netherlands Institute for Radio Astronomy, Oude Hoogeveensedijk 4, 7991 PD Dwingeloo, The Netherlands
⁸ INAF, Osservatorio Astronomico di Capodimonte, Salita Moiariello 16, 80131 Napoli, Italy
⁹ Instituto de Astrofisica de Canarias, Via Lactea, La Laguna, 38200 Santa Cruz de Tenerife, Spain
¹⁰ INAF, Osservatorio Astronomico di Padova, Vicolo dell’Osservatorio 5, 35122 Padova, Italy
¹¹ Università degli Studi di Cagliari, Dipartimento di Fisica, S.P. Monserrato-Sestu km 0,700, 09042 Monserrato, CA, Italy
¹² INAF, Osservatorio Astronomico di Roma, Via Frascati 33, 00078 Monteporzio Catone, Roma, Italy
¹³ INAF, Istituto di Astrofisica e Planetologia Spaziali, Via Fosso del Cavaliere 100, 00133 Roma, Italy
¹⁴ Sapienza Università di Roma, Piazzale Aldo Moro 5, 00185 Roma, Italy
¹⁵ Center for Astro, Particle and Planetary Physics, New York University Abu Dhabi, PO Box 129188, Abu Dhabi, UAE
¹⁶ Center of Studies and Activities for Space (CISAS) ‘G. Colombo’, University of Padova, Via Venezia 15, 35131 Padova, Italy
¹⁷ Anton Pannekoek Institute for Astronomy, University of Amsterdam, Science Park 904, 1098 XH Amsterdam, The Netherlands
¹⁸ Department of Physics, McGill University, 3600 University Street, Montréal, QC H3A 2T8, Canada
¹⁹ McGill Space Institute, McGill University, 3550 University Street, Montréal, QC H3A 2A7, Canada
²⁰ Università degli Studi di Padova, Dipartimento di Fisica e Astronomia, Via F. Marzolo 8, 35131 Padova, Italy

Received: 6 December 2020
Accepted: 7 March 2021

Abstract

We present simultaneous multiwavelength observations of the 4.66 ms redback pulsar PSR J1048+2339. We performed phase-resolved spectroscopy with the Very Large Telescope (VLT) searching for signatures of a residual accretion disk or intra-binary shock emission, constraining the companion radial velocity semi-amplitude (K₂), and estimating the neutron star mass (M_NS). Using the FORS2-VLT intermediate-resolution spectra, we measured a companion velocity of 291 < K₂ < 348 km s⁻¹ and a binary mass ratio of 0.209 < q < 0.250. Combining our results for K₂ and q, we constrained the mass of the neutron star and the companion to (1.0 < M_NS < 1.6) sin⁻³ i M_⊙ and (0.24 < M₂ < 0.33) sin⁻³i M_⊙, respectively, where i is the system inclination. The Doppler map of the Hα emission line exhibits a spot feature at the expected position of the companion star and an extended bright spot close to the inner Lagrangian point. We interpret this extended emission as the effect of an intra-binary shock originating from the interaction between the pulsar relativistic wind and the matter leaving the companion star. The mass loss from the secondary star could be either due to Roche-lobe overflow or to the ablation of its outer layer by the energetic pulsar wind. Contrastingly, we find no evidence for an accretion disk. We report on the results of the Sardinia Radio Telescope (SRT) and the Low-Frequency Array (LOFAR) telescope simultaneous radio observations at three different frequencies (150 MHz, 336 MHz, and 1400 MHz). No pulsed radio signal is found in our search. This is probably due to both scintillation and the presence of material expelled from the system which can cause the absorption of the radio signal at low frequencies. The confirmation of this hypothesis is given by another SRT observation (L-band) taken in 2019, in which a pulsed signal is detected. Finally, we report on an attempt to search for optical pulsations using IFI+Iqueye mounted at the 1.2 m Galileo telescope at the Asiago Observatory.