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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"

5515 results found.

  1. EP250806a: Liverpool telescope optical upper limit
  2. GRB 250807A: Swift detection of a burst with an optical counterpart
  3. EP250802a: additional Liverpool Telescope upper limits
  4. Fermi Gamma-ray Burst Monitor trigger 775945985/250803856 is not a GRB
  5. EP250802a: Liverpool Telescope optical upper limits
  6. EP250802a: Global MASTER-Net observations report
  7. EP250802a: GROWTH-India Telescope optical upper limit
  8. EP250730a: Global MASTER-Net observations report
  9. GRB 250728A: COLIBRÍ optical upper limit
  10. GRB 250727A: Swift-XRT observations
  11. LIGO/Virgo/KAGRA S250727cl: Identification of a GW compact binary merger candidate
  12. GRB 250725A: Swift detection of a burst
  13. The SVOM alert sb25072103 is not due to a GRB, but to a new galactic transient SVOM J195836+32283.
  14. Swift Trigger 1334535 / GRB 250718A: COLIBRÍ optical upper limits
  15. GRB 250716A: Lesedi Detection of Fading Optical Transient GOTO25eyp
  16. GRB 250717A: Fermi GBM Final Real-time Localization
  17. GRB 250716A: GOTO tentative optical counterpart candidate
  18. Fermi GRB 250716A: Global MASTER-Net observations report
  19. Fermi GRB 250715A: Global MASTER-Net observations report
  20. GRB 250702B,D,E / EP250702a: H.E.S.S. very-high-energy gamma-ray observations
  21. Fermi GRB 250714A: Global MASTER-Net observations report
  22. GRB 250706B/C: 7DT Follow-up Observations
  23. EP250711a: COLIBRÍ refined photometry and optical confirmation of the candidate
  24. EP250711a: NOT optical counterpart candidate
  25. EP candidate (ID=08500000365): COLIBRÍ optical Upper limit
  26. Fermi GRB 250711A: Global MASTER-Net observations report
  27. LIGO/Virgo/KAGRA S250711q: Identification of a GW compact binary merger candidate
  28. GRB 250702B,D,E / EP250702a: ALMA detection
  29. GRB 250702B,D,E/EP250702A: MeerKAT radio observations at 1.28GHz
  30. GRB 250702B,D,E / EP250702a: 10 GHz detection with the VLA
  31. IPN triangulation of GRB 250704B (short/hard, consistent with EP 250704a)
  32. IceCube-250706A: No Candidates from the Zwicky Transient Facility
  33. GRB 250704B / EP250704a: VLA radio detection
  34. GRB 250704B / EP250704a: Mondy and AbAO optical observations
  35. GRB 250704A: SVOM/COLIBRÍ (FM-GFT) optical observations
  36. GRB 250706B: Swift/UVOT Detection
  37. EP250702a/ GRB 250702B: NuSTAR X-ray Observations
  38. IceCube-250706A: COLIBRÍ optical upper limits
  39. GRB250706B: Swift-XRT counterpart detection
  40. GRB 250706B: iTelescope optical observations
  41. GRB 250706B: TRT bright optical counterpart detection
  42. GRB 250703A: EIRSAT-1 GMOD Detection
  43. GRB 250702F: Calapai Observatory, Massa S. Giorgio (Messina), optical observation.
  44. EP250704a / GRB 250704B: NOT observations of the optical afterglow
  45. EP250704a / GRB 250704B: VLT/X-shooter spectroscopic redshift z = 0.661
  46. GRBs 250702B,D,E / EP250702a: fast fading, extremely red counterpart
  47. GRB 250702F: GROWTH-India Telescope optical observations
  48. EP250704a: COLIBRÍ optical counterpart candidate
  49. GRB 250702F: optical photometry from Konkoly
  50. Fermi GRB 250703A: Global MASTER-Net observations report
  51. GRB 250702F: AKO Optical Afterglow Detection
  52. GRBs 250702B,C,D,E / EP250702a: VLT/HAWK-I NIR candidate
  53. GRBs 250702B,C,D,E / EP250702a: SVOM/GRM observation
  54. GRB 250702B,C,D,E/EP250702a: COLIBRÍ optical upper limit
  55. GRB 250702F: TRT Optical Observation
  56. GRB 250703A: DDOTI Optical Upper Limit
  57. EP250702a: Global MASTER-Net observations report
  58. GRB 250702F: DDOTI Optical Observation
  59. EP250702a/GRB 250702B,C,D,E: GOTO optical upper limits
  60. GRB 250702F: COLIBRÍ Observations of the Afterglow
  61. Fermi GRB 250702E: Global MASTER-Net observations report
  62. Fermi GRB 250702B: Global MASTER-Net observations report
  63. GRB 250628B: Swift-XRT observations
  64. GRB 250625A: SAO RAS possible optical afterglow
  65. GRB 250617B: Mondy and SAO RAS optical observations on 2025-06-23, 2025-06-24
  66. Fermi GRB 250623A: Global MASTER-Net observations report
  67. GRB 250617B: NUTTelA-TAO early time optical observations
  68. GRB 250617B: GOTO optical upper limit
  69. Fermi trigger No 771752663: Global MASTER-Net observations report
  70. Fermi trigger No 771718064: Global MASTER-Net observations report
  71. sb25061207: SVOM/COLIBRÍ (FM-GFT) optical upper limit
  72. GRB 250612B (250612519/771424081): Fermi GBM Final Localization
  73. Swift GRB250612.04: Global MASTER-Net observations report
  74. EP250610a: Global MASTER-Net observations report
  75. EP250610a: Swift-XRT counterpart detection
  76. Fermi trigger No 771072240: Global MASTER-Net observations report
  77. GRB 250529A: GOTO optical counterpart candidate (GOTO25dea/AT 2025ndt)
  78. Fermi GRB 250606A: Global MASTER-Net observations report
  79. Fermi trigger No 770867684: Global MASTER-Net observations report
  80. IPN triangulation of GRB 250404B
  81. IPN triangulation of GRB 250529A
  82. Fermi Gamma-ray Burst Monitor trigger 770675211/250603852 is not a GRB
  83. GRB 250602A: DDOTI Optical Follow-Up of the Fermi/LAT Localization
  84. Fermi trigger No 770638414: Global MASTER-Net observations report
  85. Swift GRB250603.05: Global MASTER-Net observations report
  86. GRB 250602A: Fermi GBM Observation
  87. GRB 250602A: Fermi-LAT detection
  88. Fermi GRB 250601A: Global MASTER-Net observations report
  89. GRB 250602A: Fermi GBM Final Real-time Localization
  90. Fermi GRB 250531A: Global MASTER-Net observations report
  91. EP#01709177494: Swift-XRT counterpart detection of known source
  92. GRB 250521C/ZTF25aarhkyn/AT2025mgj: COLIBRÍ optical observations
  93. Swift GRB 250530C: Global MASTER-Net observations report
  94. GRB 250529A: Fermi GBM Final Real-time Localization
  95. GRB 250521C (short): Zwicky Transient Facility identification of a possible fast optical transient counterpart
  96. Fermi trigger No 770058372: Global MASTER-Net observations report
  97. EP250526a: COLIBRÍ optical upper limits
  98. EP-WXT trigger 01709176712: SVOM/C-GFT observations of blue-to-red color variation
  99. GRB 250520A: 3 GHz MeerKAT Detection
  100. Fermi GRB 250521D: Global MASTER-Net observations report

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