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GCN Circulars

GCN Circulars are rapid astronomical bulletins submitted by and distributed to community members worldwide. They are used to share discoveries, observations, quantitative near-term predictions, requests for follow-up observations, or future observing plans related to high-energy, multi-messenger, and variable or transient astrophysical events. See the documentation for help with subscribing to or submitting Circulars.

Search for Circulars by submitter, subject, or body text (e.g. 'Fermi GRB').
To navigate to a specific circular, enter the associated Circular ID (e.g. 'gcn123', 'Circular 123', or '123').
Advanced Search

To narrow the search results, use advanced search syntax. This allows for specifying which circular field to search (submitter, subject, and/or body). For additional information, refer to the advanced search documentation.

Advanced Search Examples (click to copy):

subject:"Swift"
body:"GRB"
submitter:"Judith Racusin"
  1. GRB 250317C: GECAM-B detection
  2. GRB 250317B: OHP/T193 optical observations
  3. Fermi trigger No 763933627: Global MASTER-Net observations report
  4. GRB250312A: Swift/UVOT Upper Limits
  5. GRB 250317B: REM optical/NIR observations
  6. GRB 250317B: Swift-XRT observations
  7. GRB 250316A: Swift/UVOT Upper Limits
  8. GRB 250314A: REM optical/NIR upper limits
  9. GRB 250316A: AbAO AS-32 Optical Upper Limit
  10. EP 250317B: Fading optical counterpart detection by LCO
  11. GRB 250316A: Swift-XRT afterglow detection
  12. GRB 250317B: LCO detection of the fading optical afterglow
  13. GRB 250317B: refined SVOM/MXT analysis
  14. GRB250317B: SVOM/VT detection of an optical candidate from VHF data
  15. GRB 250317B: SVOM/F-GFT (COLIBRÍ) Detection of a Fading Optical Counterpart
  16. GRB 250317B: SVOM detection of a burst / correction to GRB name of GCN 39752
  17. GRB 250317B: SVOM detection of a burst
  18. GRB 250316A: Fermi GBM Observation
  19. GRB 250316A: Swift-XRT observations
  20. Fermi trigger No 763862734: Global MASTER-Net observations report
  21. GRB 250317A: Fermi GBM Final Real-time Localization
  22. Fermi GRB 250316A: Global MASTER-Net observations report
  23. GRB 250314A: SVOM/GRM analysis
  24. GRB 250316A: Swift ToO observations
  25. GRB 250316A: Swift/BAT-GUANO arcminute localization of a burst
  26. GRB 250314A: GTC z-band upper limit and updated photo-z ~ 7.27
  27. The EP-WXT trigger 01709132801 is likely a flaring star
  28. GRB 250316A: Fermi GBM Final Real-time Localization
  29. GRB 250315A/EP250315A: Fermi-GBM Sub-Threshold Detection
  30. GRB 250314A: EP-FXT afterglow detection
  31. EP250315a: refined analysis of the EP-WXT and EP-FXT observations
  32. GRB 250314A: Swift/UVOT Upper Limits
  33. GRB 250312B: GRBAlpha detection
  34. GRB 250313.89 / Fermi trigger 763594063: bright OT AT 2025ehi detection
  35. GRB 250314A: Swift XRT Detection
  36. EP250315a: optical counterpart candidate detected by Gemini North
  37. GRB 250314A: VLT/X-shooter dropout, redshift z ~ 7.3
  38. EP250315a: Einstein Probe detection of an X-ray transient
  39. GRB 250226A: Mondy AZT-33IK and Koshka Zeiss-1000 Optical Upper Limits
  40. SVOM/MXT upper limit on GRB 250314A
  41. GRB 250314A: SVOM/VT upper limit
  42. GRB 250314A: NOT near-infrared candidate counterpart
  43. GRB 250313A: Fermi GBM Detection
  44. GRB 250313A: CALET Gamma-Ray Burst Monitor detection
  45. GRB 250312B: Fermi GBM Observation
  46. GRB 250313A: Swift-XRT observations
  47. GRB250314A: SVOM/VT lack of bright optical candidate from VHF data
  48. Konus-Wind detection of GRB 250313A
  49. Konus-Wind detection of GRB 250308A
  50. GRB 250314A: SVOM detection of a burst
  51. EP250311a/GRB 250311A: Correction to EP-WXT detection time
  52. GRB 250313B: SVOM/GRM observation of a soft bright short burst
  53. GRB 250313A: SVOM/GRM observation of a bright long burst
  54. FRB 20250206A: Nondetection of Repeating Bursts from FRB 20250206A with FAST
  55. GRB 250313A: AstroSat CZTI detection of a bright long burst
  56. IceCube-250309A: MASTER detection of J140105.33-091631.6 blazar flare with Zhirkov effect
  57. Fermi trigger No 763581136: Global MASTER-Net observations report
  58. GRB 250313A: Fermi-LAT detection
  59. GRB 250313A: Swift ToO observations
  60. EP250304a: Pan-STARRS r and i-band imaging and photometry
  61. GRB 250312B: Swift/BAT-GUANO localization skymap of a burst
  62. EP trigger ID 01709061302: Lick/Kast spectroscopy with the 3 m Shane telescope
  63. Fermi GRB 250313A: Global MASTER-Net observations report
  64. GRB 250309B: PRIME near-infrared upper limits in 2nd epoch
  65. GRB 250313A???: BALROG localization (Fermi Trigger / GRB 250313607)
  66. GRB 250313A: Fermi GBM Final Real-time Localization
  67. The EP-WXT trigger 01709132551 is not a real source
  68. EP250304a: SVOM/VT optical observation
  69. EP250311a/GRB 250311A: EP-FXT follow-up observation
  70. ATCA detection of the radio counterpart of GRB 250309B-AT2025dws
  71. EP250302a: Chandra X-ray Detection
  72. GRB 250312A: Swift-XRT refined Analysis
  73. Fermi Gamma-ray Burst Monitor trigger 763509110/250312911 is not a GRB
  74. Fermi trigger No 763509110: Global MASTER-Net observations report
  75. Fermi GRB 250312B: Global MASTER-Net observations report
  76. GRB 250312A: Enhanced Swift-XRT position
  77. GRB 250312B: Fermi GBM Final Localization
  78. LIGO/Virgo/KAGRA S250304cb: Upper limits from Swift/BAT-GUANO
  79. GRB 250226B: Fermi GBM Observation
  80. Swift GRB 250312A: Global MASTER-Net observations report
  81. GRB 250302A: Fermi GBM Observation
  82. GRB 250309B/AT2025dws: Daochen/RC-10 optical counterpart observation
  83. GRB 250312A: Swift detection of a burst
  84. GRB 241213A: VIRT Optical Upper Limit
  85. GRB 241228A: VIRT Optical Upper Limit
  86. GRB 250311A/EP250311a: Optical upper limits with Kinder observations
  87. GRB 250223B: Fermi GBM Observation
  88. GRB 250311A: Swift-XRT observations
  89. GRB 250228A: Fermi GBM Observation
  90. GRB 250309B: 1.3m DFOT Optical observations
  91. IceCube-250309A: Upper limits from a search for additional neutrino events in IceCube
  92. EP250311a: Global MASTER-Net observations report
  93. GRB 250308A: Swift/BAT-GUANO localization skymap of a short burst
  94. GRB 250302A: Swift/BAT-GUANO localization skymap of a burst
  95. GRB 250228A: Swift/BAT-GUANO localization skymap of a likely short burst
  96. GRB 250226B: Swift/BAT-GUANO localization skymap of a likely long GRB
  97. GRB 250226A: Swift/BAT-GUANO localization skymap of a long GRB
  98. GRB 250223B: Swift/BAT-GUANO localization skymap of a short burst
  99. GRB 250309B: PRIME near-infrared detection
  100. EP250304a: Chandra detection

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