FRB 121102: Detection at 4 - 8 GHz band with Breakthrough Listen backend at Green Bank

ATel #10675; Gajjar, Vishal (University of California, Berkeley, USA), Andrew P. V. Siemion (University of California, Berkeley, USA), David H. E. MacMahon (University of California, Berkeley, USA), Steve Croft (University of California, Berkeley, USA), Gregory Hellbourg (University of California, Berkeley, USA), Howard Isaacson (University of California, Berkeley, USA), J. Emilio Enriquez (University of California, Berkeley, USA), Danny C. Price (University of California, Berkeley, USA), Matthew Lebofsky (University of California, Berkeley, USA), David DeBoer (University of California, Berkeley, USA), Dan Werthimer (University of California, Berkeley, USA), Jack Hickish (University of California, Berkeley, USA), Casey Brinkman (University of Vermont, Burlington, USA), Shami Chatterjee (University of Cornell, Ithaca, USA), Scott Ransom (University of Virginia, Charlottesville, USA)
on 29 Aug 2017; 03:11 UT
Distributed as an Instant Email Notice Transients
Credential Certification: Steve Croft (scroft@astro.berkeley.edu)

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On Saturday, August 26 at 13:51:44 UTC we initiated observations of the well-known repeating fast radio burst FRB 121102 [Spitler et al., Nature, 531, 7593 202-205, 2016] using the Breakthrough Listen Digital Backend with the C-band receiver at the Green Bank Telescope. We recorded baseband voltage data across 5.4375 GHz of bandwidth, completely covering the C-band receiver's nominal 4-8 GHz band [MacMahon et al. arXiv:1707.06024v2]. Observations were conducted over ten 30-minute scans, as detailed in Table 1. Immediately after observations, the baseband data were reduced to form high time resolution (300 us integration) Stokes-I products using a GPU-accelerated spectroscopy suite. These reduced products were searched for dispersed pulses consistent with the known dispersion measure of FRB 121102 (557 pc cm^-3); baseband voltage data were preserved. We detected 15 bursts above our detection threshold of 10 sigma in the first two 30-minute scans, denoted 11A-L and 12A-B in Table 2. In Table 2, we include the detection signal-to-noise ratio (SNR) of each burst, along with a very rough estimate of pulse energy density assuming a 12 Jy system equivalent flux density, 300 us pulse width, and uniform 3800 MHz bandwidth. We note the following phenomenological properties of the detected bursts: 1. Bursts show marked changes in spectral extent, with characteristic spectral structure in the 100 MHz - 1 GHz range. 2. Several bursts appear to peak in brightness at frequencies above 6 GHz.

 
Table 1:  
 
Scan No. |    MJD        |    Duration (min)  | No. Bursts detected  
----------------------------------------------------------------------- 
11       |  57991.5776   |        30          |       12      
12       |  57991.5986   |        30          |       3  
13       |  57991.6196   |        30          |       0 
14       |  57991.6406   |        30          |       0 
15       |  57991.6616   |        30          |       0  
16       |  57991.6825   |        30          |       0 
17       |  57991.7035   |        30          |       0 
18       |  57991.7245   |        30          |       0 
19       |  57991.7454   |        30          |       0 
20       |  57991.7664   |        20          |       0 
 

 
Table 2: 
 
 
Burst   | SNR* | Energy Density   |    Time*       | Sample  
        |      |    (Jy us)       |     (s)        |        
------------------------------------------------------------- 
11G     | 60.6 |     144.5        |    597.612     | 1709782  
11A     | 47.9 |     114.2        |    16.2505     | 46493    
11C     | 47.2 |     112.5        |    323.352     | 925118   
11D     | 25.6 |     61.0         |    344.768     | 986388   
11E     | 24.6 |     58.7         |    356.033     | 1018619  
11F     | 21.2 |     50.5         |    356.034     | 1018620  
11L     | 20.8 |     49.6         |    1454.55     | 4161497  
12B     | 20.7 |     49.4         |    743.071     | 2125942  
12A     | 13.6 |     32.4         |    104.922     | 300184   
11J     | 12.3 |     29.3         |    1036.42     | 2965234  
11I     | 11.6 |     27.7         |    769.864     | 2202599  
11K     | 11.1 |     26.5         |    1142.41     | 3268458  
12C     | 10.8 |     25.7         |    1526.39     | 4367026  
11H     | 10.6 |     25.3         |    691.83      | 1979341  
11B     | 10.4 |     24.8         |    285.436     | 816640   
 
* seconds from tstart = MJD 57991.5776 
 

These are the highest frequency and widest bandwidth detections of bursts from FRB 121102 obtained to-date. Additional fully calibrated full-Stokes analysis employing coherent dedispersion on raw voltage data is ongoing. These observations may indicate FRB 121102 is currently in a heightened activity state [Law et al. arXiv:1705.07553], and follow-on observations are encouraged, particularly at higher radio frequencies.

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