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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. LIGO/Virgo/KAGRA S250319bu: Updated Sky localization
  2. GRB 250314A: ATCA radio upper limits
  3. EP250302a: VLA observations
  4. GRB 250317B: OHP/T193 continued follow-up
  5. LIGO/Virgo/KAGRA S250319bu: Identification of a GW compact binary merger candidate
  6. GRB 250317C: SVOM/GRM observation of a long burst
  7. GRB 250317B: Leavitt Observatory optical upper limit
  8. GRB 250309B/AT2025dws: further ATCA observations
  9. GRB 250317B: Mondy AZT-33IK Optical Observations
  10. GRB 250317C: AstroSat CZTI detection
  11. GRB 250317B: NOT optical observations suggest an optical plateau phase
  12. GRB 250317B: GTC/OSIRIS+ spectroscopic redshift z=3.44
  13. GRB 250317C: GECAM-B detection
  14. GRB 250317B: OHP/T193 optical observations
  15. Fermi trigger No 763933627: Global MASTER-Net observations report
  16. GRB250312A: Swift/UVOT Upper Limits
  17. GRB 250317B: REM optical/NIR observations
  18. GRB 250317B: Swift-XRT observations
  19. GRB 250316A: Swift/UVOT Upper Limits
  20. GRB 250314A: REM optical/NIR upper limits
  21. GRB 250316A: AbAO AS-32 Optical Upper Limit
  22. EP 250317B: Fading optical counterpart detection by LCO
  23. GRB 250316A: Swift-XRT afterglow detection
  24. GRB 250317B: LCO detection of the fading optical afterglow
  25. GRB 250317B: refined SVOM/MXT analysis
  26. GRB250317B: SVOM/VT detection of an optical candidate from VHF data
  27. GRB 250317B: SVOM/F-GFT (COLIBRÍ) Detection of a Fading Optical Counterpart
  28. GRB 250317B: SVOM detection of a burst / correction to GRB name of GCN 39752
  29. GRB 250317B: SVOM detection of a burst
  30. GRB 250316A: Fermi GBM Observation
  31. GRB 250316A: Swift-XRT observations
  32. Fermi trigger No 763862734: Global MASTER-Net observations report
  33. GRB 250317A: Fermi GBM Final Real-time Localization
  34. Fermi GRB 250316A: Global MASTER-Net observations report
  35. GRB 250314A: SVOM/GRM analysis
  36. GRB 250316A: Swift ToO observations
  37. GRB 250316A: Swift/BAT-GUANO arcminute localization of a burst
  38. GRB 250314A: GTC z-band upper limit and updated photo-z ~ 7.27
  39. The EP-WXT trigger 01709132801 is likely a flaring star
  40. GRB 250316A: Fermi GBM Final Real-time Localization
  41. GRB 250315A/EP250315A: Fermi-GBM Sub-Threshold Detection
  42. GRB 250314A: EP-FXT afterglow detection
  43. EP250315a: refined analysis of the EP-WXT and EP-FXT observations
  44. GRB 250314A: Swift/UVOT Upper Limits
  45. GRB 250312B: GRBAlpha detection
  46. GRB 250313.89 / Fermi trigger 763594063: bright OT AT 2025ehi detection
  47. GRB 250314A: Swift XRT Detection
  48. EP250315a: optical counterpart candidate detected by Gemini North
  49. GRB 250314A: VLT/X-shooter dropout, redshift z ~ 7.3
  50. EP250315a: Einstein Probe detection of an X-ray transient
  51. GRB 250226A: Mondy AZT-33IK and Koshka Zeiss-1000 Optical Upper Limits
  52. SVOM/MXT upper limit on GRB 250314A
  53. GRB 250314A: SVOM/VT upper limit
  54. GRB 250314A: NOT near-infrared candidate counterpart
  55. GRB 250313A: Fermi GBM Detection
  56. GRB 250313A: CALET Gamma-Ray Burst Monitor detection
  57. GRB 250312B: Fermi GBM Observation
  58. GRB 250313A: Swift-XRT observations
  59. GRB250314A: SVOM/VT lack of bright optical candidate from VHF data
  60. Konus-Wind detection of GRB 250313A
  61. Konus-Wind detection of GRB 250308A
  62. GRB 250314A: SVOM detection of a burst
  63. EP250311a/GRB 250311A: Correction to EP-WXT detection time
  64. GRB 250313B: SVOM/GRM observation of a soft bright short burst
  65. GRB 250313A: SVOM/GRM observation of a bright long burst
  66. FRB 20250206A: Nondetection of Repeating Bursts from FRB 20250206A with FAST
  67. GRB 250313A: AstroSat CZTI detection of a bright long burst
  68. IceCube-250309A: MASTER detection of J140105.33-091631.6 blazar flare with Zhirkov effect
  69. Fermi trigger No 763581136: Global MASTER-Net observations report
  70. GRB 250313A: Fermi-LAT detection
  71. GRB 250313A: Swift ToO observations
  72. EP250304a: Pan-STARRS r and i-band imaging and photometry
  73. GRB 250312B: Swift/BAT-GUANO localization skymap of a burst
  74. EP trigger ID 01709061302: Lick/Kast spectroscopy with the 3 m Shane telescope
  75. Fermi GRB 250313A: Global MASTER-Net observations report
  76. GRB 250309B: PRIME near-infrared upper limits in 2nd epoch
  77. GRB 250313A???: BALROG localization (Fermi Trigger / GRB 250313607)
  78. GRB 250313A: Fermi GBM Final Real-time Localization
  79. The EP-WXT trigger 01709132551 is not a real source
  80. EP250304a: SVOM/VT optical observation
  81. EP250311a/GRB 250311A: EP-FXT follow-up observation
  82. ATCA detection of the radio counterpart of GRB 250309B-AT2025dws
  83. EP250302a: Chandra X-ray Detection
  84. GRB 250312A: Swift-XRT refined Analysis
  85. Fermi Gamma-ray Burst Monitor trigger 763509110/250312911 is not a GRB
  86. Fermi trigger No 763509110: Global MASTER-Net observations report
  87. Fermi GRB 250312B: Global MASTER-Net observations report
  88. GRB 250312A: Enhanced Swift-XRT position
  89. GRB 250312B: Fermi GBM Final Localization
  90. LIGO/Virgo/KAGRA S250304cb: Upper limits from Swift/BAT-GUANO
  91. GRB 250226B: Fermi GBM Observation
  92. Swift GRB 250312A: Global MASTER-Net observations report
  93. GRB 250302A: Fermi GBM Observation
  94. GRB 250309B/AT2025dws: Daochen/RC-10 optical counterpart observation
  95. GRB 250312A: Swift detection of a burst
  96. GRB 241213A: VIRT Optical Upper Limit
  97. GRB 241228A: VIRT Optical Upper Limit
  98. GRB 250311A/EP250311a: Optical upper limits with Kinder observations
  99. GRB 250223B: Fermi GBM Observation
  100. GRB 250311A: Swift-XRT observations

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