High-frequency Fast Radio Burst Search of Nearby Star-forming Galaxies M77 and M82

Abstract The astrophysical origins of fast radio bursts (FRBs) are still unknown, but magnetars are a strong candidate for producing at least some FRBs. To investigate the magnetar progenitor model, we conducted a deep search of M77 and M82, two nearby galaxies with high star formation rates that could potentially harbor large magnetar populations. Using one of the 34 m dishes in the Deep Space Network, we observed the two galaxies at 8.4 GHz for about 100 hr each. At this observing frequency, we are unaffected by the potentially extreme temporal broadening caused by multipath scattering in the turbulent inner regions of the galaxies. We do not detect any FRBs from either galaxy above a fluence detection threshold of <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" overflow="scroll"> <mml:msub> <mml:mrow> <mml:mi>F</mml:mi> </mml:mrow> <mml:mrow> <mml:mi mathvariant="normal">min</mml:mi> </mml:mrow> </mml:msub> <mml:mo>=</mml:mo> <mml:mn>1.3</mml:mn> <mml:mspace width="0.25em"/> <mml:mi mathvariant="normal">Jy</mml:mi> <mml:mspace width="0.25em"/> <mml:mi mathvariant="normal">ms</mml:mi> </mml:math> , which corresponds to an isotropic energy equivalent of <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" overflow="scroll"> <mml:msub> <mml:mrow> <mml:mi>E</mml:mi> </mml:mrow> <mml:mrow> <mml:mi mathvariant="normal">iso,min</mml:mi> </mml:mrow> </mml:msub> <mml:mo>=</mml:mo> <mml:mn>2.7</mml:mn> <mml:mo>×</mml:mo> <mml:mn>1</mml:mn> <mml:msup> <mml:mrow> <mml:mn>0</mml:mn> </mml:mrow> <mml:mrow> <mml:mn>36</mml:mn> </mml:mrow> </mml:msup> <mml:mspace width="0.25em"/> <mml:mi mathvariant="normal">erg</mml:mi> </mml:math> for M77 and <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" overflow="scroll"> <mml:msub> <mml:mrow> <mml:mi>E</mml:mi> </mml:mrow> <mml:mrow> <mml:mi mathvariant="normal">iso,min</mml:mi> </mml:mrow> </mml:msub> <mml:mo>=</mml:mo> <mml:mn>1.7</mml:mn> <mml:mo>×</mml:mo> <mml:mn>1</mml:mn> <mml:msup> <mml:mrow> <mml:mn>0</mml:mn> </mml:mrow> <mml:mrow> <mml:mn>35</mml:mn> </mml:mrow> </mml:msup> <mml:mspace width="0.25em"/> <mml:mi mathvariant="normal">erg</mml:mi> </mml:math> for M82. Based on the nondetections, we set a 95% upper limit to the 8.4 GHz burst rate of R 95 = 273 yr −1 and R 95 = 233 yr −1 for M77 and M82, respectively. By estimating the magnetar population in each galaxy, we set an upper limit to the burst rate per magnetar of <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" overflow="scroll"> <mml:msub> <mml:mrow> <mml:mi>r</mml:mi> </mml:mrow> <mml:mrow> <mml:mi mathvariant="normal">max</mml:mi> </mml:mrow> </mml:msub> <mml:mo>≈</mml:mo> <mml:mn>1</mml:mn> <mml:mspace width="0.25em"/> <mml:msup> <mml:mrow> <mml:mi mathvariant="normal">magnetar</mml:mi> </mml:mrow> <mml:mrow> <mml:mo>−</mml:mo> <mml:mn>1</mml:mn> </mml:mrow> </mml:msup> <mml:mspace width="0.25em"/> <mml:msup> <mml:mrow> <mml:mi mathvariant="normal">yr</mml:mi> </mml:mrow> <mml:mrow> <mml:mo>−</mml:mo> <mml:mn>1</mml:mn> </mml:mrow> </mml:msup> </mml:math> . Unlike previous searches of these galaxies at frequencies of ν ≲ 1.5 GHz, our results give a scattering-independent limit to the burst rate.