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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"

20949 results found.

  1. GRB 250321B: Swift-XRT observations
  2. FRB 250316A: DDOTI Continued Optical Observations (Third Epoch)
  3. GRB 250322A: Gemini-North redshift of candidate host galaxy
  4. EP250304a: VLT/MUSE spectroscopic observation of its associated supernova SN 2025fhm
  5. GRB250322A: STEP/T80S optical limits
  6. GRB 250322A: Gemini-South optical observations
  7. GRB 250322A: VLT optical observations
  8. GRB 250322A: VLT near-infrared observations
  9. FRB 250316A: DDOTI Continued Optical Observations
  10. GRB 250321B: SVOM/COLIBRÍ (F-GFT) follow-up observations
  11. FRB 20250316A: Kinder optical upper limits of the Einstein Probe candidate X-ray source EP J120944.2+585060
  12. GRB 250322A: MASTER optical observation
  13. EP250321a: Liverpool Telescope optical follow-up
  14. EP250321a: Mondy AZT-33IK Optical Observations
  15. FRB 20250316A: detection of a candidate associated X-ray source EP J120944.2+585060 by Einstein Probe
  16. EP250321a: refined analysis of the EP-WXT and EP-FXT observations
  17. EP250321a: KAIT optical observations
  18. EP250321A: COLIBRÍ Continuing Optical Observations
  19. GRB 250321B: Swift ToO observations
  20. EP250321a: WFST optical observations
  21. EP250321a: Xinglong 216 decaying optical observations
  22. EP250321a: SVOM/VT optical observation
  23. EP 250321A: Optical counterpart detection by LCO.
  24. EP250321a: Kinder optical follow-up observations
  25. GRB 250321A: Swift/UVOT Upper Limits
  26. EP250321a: LCO optical counterpart detection
  27. EP250321A: COLIBRÍ Optical Observations
  28. EP250321a: VLT/X-shooter redshift z = 4.368
  29. EP250321a: REM optical/NIR afterglow detection
  30. Fermi GRB 250320B: Global MASTER-Net observations report
  31. EP250321a: Global MASTER-Net observations report
  32. Swift GRB 250321A: Global MASTER-Net observations report
  33. Fermi GRB 250321A: Global MASTER-Net observations report
  34. GRB 250321A: GOTO optical upper limits
  35. GRB 250314A: Keck/NIRC2 J-band upper limit
  36. EP250226a/GRB 250226A: KAIT optical observations
  37. GRB 250309B: Proof-of-concept for Joint ZTF+EP Experiment
  38. GRB 250317B: Mondy AZT-33IK Continued Optical Observations
  39. Fermi GRB 250319B: Global MASTER-Net observations report
  40. FRB 20250316A: Upper limits for gamma-ray transient from Insight-HXMT/HE observations
  41. LIGO/Virgo/KAGRA S250206dm: LIGHETR followup observations of AT2025azn
  42. GRB 250317B: SVOM/COLIBRI (F-GFT) follow-up observations
  43. GRB 250314A: ATCA radio upper limits
  44. EP250302a: VLA observations
  45. GRB 250317B: OHP/T193 continued follow-up
  46. GRB 250317B: Leavitt Observatory optical upper limit
  47. GRB 250309B/AT2025dws: further ATCA observations
  48. GRB 250317B: Mondy AZT-33IK Optical Observations
  49. GRB 250317B: NOT optical observations suggest an optical plateau phase
  50. GRB 250317B: GTC/OSIRIS+ spectroscopic redshift z=3.44
  51. GRB 250317B: OHP/T193 optical observations
  52. Fermi trigger No 763933627: Global MASTER-Net observations report
  53. GRB250312A: Swift/UVOT Upper Limits
  54. GRB 250317B: REM optical/NIR observations
  55. GRB 250317B: Swift-XRT observations
  56. GRB 250314A: REM optical/NIR upper limits
  57. GRB 250316A: AbAO AS-32 Optical Upper Limit
  58. EP 250317B: Fading optical counterpart detection by LCO
  59. GRB 250316A: Swift-XRT afterglow detection
  60. GRB 250317B: LCO detection of the fading optical afterglow
  61. GRB 250317B: SVOM/F-GFT (COLIBRÍ) Detection of a Fading Optical Counterpart
  62. GRB 250316A: Swift-XRT observations
  63. Fermi trigger No 763862734: Global MASTER-Net observations report
  64. Fermi GRB 250316A: Global MASTER-Net observations report
  65. GRB 250316A: Swift ToO observations
  66. GRB 250316A: Swift/BAT-GUANO arcminute localization of a burst
  67. GRB 250314A: EP-FXT afterglow detection
  68. EP250315a: refined analysis of the EP-WXT and EP-FXT observations
  69. GRB 250313.89 / Fermi trigger 763594063: bright OT AT 2025ehi detection
  70. GRB 250314A: Swift XRT Detection
  71. GRB 250314A: VLT/X-shooter dropout, redshift z ~ 7.3
  72. GRB 250226A: Mondy AZT-33IK and Koshka Zeiss-1000 Optical Upper Limits
  73. GRB 250314A: NOT near-infrared candidate counterpart
  74. GRB 250313A: Swift-XRT observations
  75. Fermi trigger No 763581136: Global MASTER-Net observations report
  76. GRB 250313A: Swift ToO observations
  77. EP trigger ID 01709061302: Lick/Kast spectroscopy with the 3 m Shane telescope
  78. Fermi GRB 250313A: Global MASTER-Net observations report
  79. GRB 250309B: PRIME near-infrared upper limits in 2nd epoch
  80. EP250304a: SVOM/VT optical observation
  81. ATCA detection of the radio counterpart of GRB 250309B-AT2025dws
  82. EP250302a: Chandra X-ray Detection
  83. Fermi trigger No 763509110: Global MASTER-Net observations report
  84. Fermi GRB 250312B: Global MASTER-Net observations report
  85. Swift GRB 250312A: Global MASTER-Net observations report
  86. GRB 250309B/AT2025dws: Daochen/RC-10 optical counterpart observation
  87. GRB 250311A/EP250311a: Optical upper limits with Kinder observations
  88. GRB 250311A: Swift-XRT observations
  89. GRB 250309B: 1.3m DFOT Optical observations
  90. EP250311a: Global MASTER-Net observations report
  91. GRB 250309B: PRIME near-infrared detection
  92. EP250304a: Chandra detection
  93. GRB 250311A/EP250311a: TRT optical upper limit
  94. IceCube-250309A: MITSuME Akeno and Seimei/TriCCS optical observations
  95. GRB 250311A: Tiled Swift observations
  96. EP250311a/GRB 250311A: EP-WXT detection
  97. GRB 250311A/MAXI J1457-026: MAXI/GSC detection
  98. GRB 250309B / AT2025dws: further SAO RAS optical observations
  99. IceCube-250309A: Upper limits from Fermi-GBM Observations
  100. GRB 250309B / AT2025dws: KMTNet-CTIO optical observations

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