A late-time radio survey of short gamma-ray bursts at z < 0.5: New constraints on the remnants of neutron-star mergers

Genevieve Schroeder; Ben Margalit; Wen Fai Fong; Brian D. Metzger; Peter K.G. Williams; Kerry Paterson; Kate D. Alexander; Tanmoy Laskar; Armaan V. Goyal; Edo Berger

doi:10.3847/1538-4357/abb407

A late-time radio survey of short gamma-ray bursts at z < 0.5: New constraints on the remnants of neutron-star mergers

Genevieve Schroeder, Ben Margalit, Wen Fai Fong, Brian D. Metzger, Peter K.G. Williams, Kerry Paterson, Kate D. Alexander, Tanmoy Laskar, Armaan V. Goyal, Edo Berger

Department of Physics

Research output: Contribution to journal › Review article › peer-review

32 Citations (SciVal)

Abstract

Massive, rapidly spinning magnetar remnants produced as a result of binary neutron-star (BNS) mergers may deposit a fraction of their energy into the surrounding kilonova ejecta, powering a synchrotron radio signal from the interaction of the ejecta with the circumburst medium. Here, we present 6.0 GHz Very Large Array (VLA) observations of nine, low-redshift short gamma-ray bursts (GRBs; z < 0.5) on rest-frame timescales of ≈2.4-13.9 yr following the bursts. We place 3σ limits on radio continuum emission of F_ν ≾ 6-20 μJy at the burst positions, or L_ν ≾ (0.6-8.3) × 10²⁸ erg s⁻¹ Hz⁻¹. Comparing these limits with new light-curve modeling that properly incorporates relativistic effects, we obtain limits on the energy deposited into the ejecta of E_ej ≾ (0.6-6.7) × 10⁵² erg (E_ej ≾ (1.8-17.6) ´ 10⁵² erg) for an ejecta mass of 0.03 M_e (0.1 M_e). We present a uniform reanalysis of 27 short GRBs with 5.5-6.0 GHz observations, and find that ≳50% of short GRBs did not form stable magnetar remnants in their mergers. Assuming short GRBs are produced by BNS mergers drawn from the Galactic BNS population plus an additional component of high-mass GW194025-like mergers in a fraction f_GW190425 of cases, we place constraints on the maximum mass of a nonrotating neutron star (NS; Tolman-Oppenheimer-Volkoff mass; M_TOV), finding M_TOV ≾ 2.23 M for f_GW190425 = 0.4; this limit increases for larger values of f_GW190425. The detection (or lack thereof) of radio remnants in untargeted surveys such as the VLA Sky Survey (VLASS) could provide more stringent constraints on the fraction of mergers that produce stable remnants. If ≳ 30-300 radio remnants are discovered in VLASS, this suggests that short GRBs are a biased population of BNS mergers in terms of the stability of the remnants they produce.

Original language	English
Article number	82
Journal	Astrophysical Journal
Volume	902
Issue number	1
DOIs	https://doi.org/10.3847/1538-4357/abb407
Publication status	Published - 10 Oct 2020

Funding

Support for G.S. in this work was provided by the NSF through Student Observing Support award SOSP19B-001 from the NRAO. The Fong Group at Northwestern acknowledges support by the National Science Foundation under grant Nos. AST-1814782 and AST-1909358. B.M. is supported by NASA through the NASA Hubble Fellowship grant #HST-HF2-51412.001-A awarded by the Space Telescope Science Institute, which is operated by the Association of Universities for Research in Astronomy, Inc., for NASA, under contract NAS5-26555. B.D.M. is supported in part by the Simons Foundation through the Simons Fellows Program (grant # 606260). K.D.A. is supported by NASA through the NASA Hubble Fellowship grant #HST-HF2-51403.001-A awarded by the Space Telescope Science Institute, which is operated by the Association of Universities for Research in Astronomy, Inc., for NASA, under contract NAS5-26555.

Keywords

Gamma-ray bursts (629)
Magnetars (992)
Neutron stars (1108)

ASJC Scopus subject areas

Astronomy and Astrophysics
Space and Planetary Science

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10.3847/1538-4357/abb407

https://arxiv.org/pdf/2006.07434.pdf

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title = "A late-time radio survey of short gamma-ray bursts at z < 0.5: New constraints on the remnants of neutron-star mergers",

abstract = "Massive, rapidly spinning magnetar remnants produced as a result of binary neutron-star (BNS) mergers may deposit a fraction of their energy into the surrounding kilonova ejecta, powering a synchrotron radio signal from the interaction of the ejecta with the circumburst medium. Here, we present 6.0 GHz Very Large Array (VLA) observations of nine, low-redshift short gamma-ray bursts (GRBs; z < 0.5) on rest-frame timescales of ≈2.4-13.9 yr following the bursts. We place 3σ limits on radio continuum emission of Fν ≾ 6-20 μJy at the burst positions, or Lν ≾ (0.6-8.3) × 1028 erg s−1 Hz−1. Comparing these limits with new light-curve modeling that properly incorporates relativistic effects, we obtain limits on the energy deposited into the ejecta of Eej ≾ (0.6-6.7) × 1052 erg (Eej ≾ (1.8-17.6) ´ 1052 erg) for an ejecta mass of 0.03 Me (0.1 Me). We present a uniform reanalysis of 27 short GRBs with 5.5-6.0 GHz observations, and find that ≳50% of short GRBs did not form stable magnetar remnants in their mergers. Assuming short GRBs are produced by BNS mergers drawn from the Galactic BNS population plus an additional component of high-mass GW194025-like mergers in a fraction fGW190425 of cases, we place constraints on the maximum mass of a nonrotating neutron star (NS; Tolman-Oppenheimer-Volkoff mass; MTOV), finding MTOV ≾ 2.23 M for fGW190425 = 0.4; this limit increases for larger values of fGW190425. The detection (or lack thereof) of radio remnants in untargeted surveys such as the VLA Sky Survey (VLASS) could provide more stringent constraints on the fraction of mergers that produce stable remnants. If ≳ 30-300 radio remnants are discovered in VLASS, this suggests that short GRBs are a biased population of BNS mergers in terms of the stability of the remnants they produce.",

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author = "Genevieve Schroeder and Ben Margalit and Fong, {Wen Fai} and Metzger, {Brian D.} and Williams, {Peter K.G.} and Kerry Paterson and Alexander, {Kate D.} and Tanmoy Laskar and Goyal, {Armaan V.} and Edo Berger",

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doi = "10.3847/1538-4357/abb407",

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AU - Schroeder, Genevieve

AU - Margalit, Ben

AU - Fong, Wen Fai

AU - Metzger, Brian D.

AU - Williams, Peter K.G.

AU - Paterson, Kerry

AU - Alexander, Kate D.

AU - Laskar, Tanmoy

AU - Goyal, Armaan V.

AU - Berger, Edo

PY - 2020/10/10

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N2 - Massive, rapidly spinning magnetar remnants produced as a result of binary neutron-star (BNS) mergers may deposit a fraction of their energy into the surrounding kilonova ejecta, powering a synchrotron radio signal from the interaction of the ejecta with the circumburst medium. Here, we present 6.0 GHz Very Large Array (VLA) observations of nine, low-redshift short gamma-ray bursts (GRBs; z < 0.5) on rest-frame timescales of ≈2.4-13.9 yr following the bursts. We place 3σ limits on radio continuum emission of Fν ≾ 6-20 μJy at the burst positions, or Lν ≾ (0.6-8.3) × 1028 erg s−1 Hz−1. Comparing these limits with new light-curve modeling that properly incorporates relativistic effects, we obtain limits on the energy deposited into the ejecta of Eej ≾ (0.6-6.7) × 1052 erg (Eej ≾ (1.8-17.6) ´ 1052 erg) for an ejecta mass of 0.03 Me (0.1 Me). We present a uniform reanalysis of 27 short GRBs with 5.5-6.0 GHz observations, and find that ≳50% of short GRBs did not form stable magnetar remnants in their mergers. Assuming short GRBs are produced by BNS mergers drawn from the Galactic BNS population plus an additional component of high-mass GW194025-like mergers in a fraction fGW190425 of cases, we place constraints on the maximum mass of a nonrotating neutron star (NS; Tolman-Oppenheimer-Volkoff mass; MTOV), finding MTOV ≾ 2.23 M for fGW190425 = 0.4; this limit increases for larger values of fGW190425. The detection (or lack thereof) of radio remnants in untargeted surveys such as the VLA Sky Survey (VLASS) could provide more stringent constraints on the fraction of mergers that produce stable remnants. If ≳ 30-300 radio remnants are discovered in VLASS, this suggests that short GRBs are a biased population of BNS mergers in terms of the stability of the remnants they produce.

AB - Massive, rapidly spinning magnetar remnants produced as a result of binary neutron-star (BNS) mergers may deposit a fraction of their energy into the surrounding kilonova ejecta, powering a synchrotron radio signal from the interaction of the ejecta with the circumburst medium. Here, we present 6.0 GHz Very Large Array (VLA) observations of nine, low-redshift short gamma-ray bursts (GRBs; z < 0.5) on rest-frame timescales of ≈2.4-13.9 yr following the bursts. We place 3σ limits on radio continuum emission of Fν ≾ 6-20 μJy at the burst positions, or Lν ≾ (0.6-8.3) × 1028 erg s−1 Hz−1. Comparing these limits with new light-curve modeling that properly incorporates relativistic effects, we obtain limits on the energy deposited into the ejecta of Eej ≾ (0.6-6.7) × 1052 erg (Eej ≾ (1.8-17.6) ´ 1052 erg) for an ejecta mass of 0.03 Me (0.1 Me). We present a uniform reanalysis of 27 short GRBs with 5.5-6.0 GHz observations, and find that ≳50% of short GRBs did not form stable magnetar remnants in their mergers. Assuming short GRBs are produced by BNS mergers drawn from the Galactic BNS population plus an additional component of high-mass GW194025-like mergers in a fraction fGW190425 of cases, we place constraints on the maximum mass of a nonrotating neutron star (NS; Tolman-Oppenheimer-Volkoff mass; MTOV), finding MTOV ≾ 2.23 M for fGW190425 = 0.4; this limit increases for larger values of fGW190425. The detection (or lack thereof) of radio remnants in untargeted surveys such as the VLA Sky Survey (VLASS) could provide more stringent constraints on the fraction of mergers that produce stable remnants. If ≳ 30-300 radio remnants are discovered in VLASS, this suggests that short GRBs are a biased population of BNS mergers in terms of the stability of the remnants they produce.

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A late-time radio survey of short gamma-ray bursts at z < 0.5: New constraints on the remnants of neutron-star mergers

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