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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 250818B: SVOM/VT optical observation
  2. GRB 250814A: Further GRAWITA TNG NIR observations
  3. GRB 250818B: Swift-XRT afterglow detection
  4. GRB 250818B: GOTO optical counterpart candidate
  5. GRB 250818B: SVOM detection of a short burst
  6. LIGO/Virgo/KAGRA S250818t: Identification of a GW compact binary merger candidate
  7. GRB 250818A: Swift detection of a burst
  8. GRB 250818A: Fermi GBM Final Real-time Localization
  9. sb25081602: Swift-XRT observations
  10. GRB 250816A: SVOM/GRM observation of a short burst
  11. SVOM/sb25081602: detection of a likely X-ray transient
  12. Fermi GRB 250814B: Global MASTER-Net observations report
  13. GRB 250816A: Fermi GBM Final Real-time Localization
  14. GRB 250814A: Swift-BAT refined analysis
  15. GRB 250815A: Fermi GBM Final Localization
  16. GRB 250813B: Liverpool Telescope optical upper limits
  17. GRB 250814A: Further COLIBRÍ optical upper limit
  18. GRB 250814A: detection of the afterglow candidate with Liverpool Telescope
  19. GRB 250814A: GRAWITA TNG NIR observations
  20. GRB 250812A: SVOM/VT optical continued observation
  21. GRB 250814A: Mondy optical observations of the candidate counterpart to LVK S250814bg
  22. GRB 250813B: Calapai Observatory, Massa S. Giorgio (Messina), upper limit
  23. GRB250814A: TRT optical upper limits
  24. GRB 250814B: SVOM/GRM observation
  25. GRB 250814C: SVOM/GRM observation of a short burst
  26. LIGO/Virgo/KAGRA S250813k: Swift XRT observations, 2 X-ray sources
  27. GRB 250813B: SVOM/GRM observation
  28. GRB 250814A: P200/WIRC observations of the afterglow candidate
  29. GRB 250814A: possible optical afterglow candidate at Spanish observatories
  30. GRB 250814A: KAIT optical upper limit
  31. GRB 250814A: Swift-XRT refined Analysis
  32. GRB 240814A: Fermi GBM Observation
  33. GRB 250814A: Possible afterglow candidate from P200/WIRC
  34. GRB 250813B: Fermi GBM Observation
  35. GRB 250814A: Optical observations with MDM Hiltner 2.4m telescope
  36. Fermi trigger No 776818276: Global MASTER-Net observations report
  37. Swift GRB250814.32: Global MASTER-Net observations report
  38. GRB 250814A: J-band upper limit from WINTER
  39. IceCube-250813A: Upper limits from a search for additional neutrino events in IceCube
  40. GRB 250813B: NOT observations of the optical afterglow
  41. GRB 250813B: SVOM/VT optical observations
  42. Subject GRB 250813B: SVOM/MXT refined analysis
  43. GRB 250814A: COLIBRÍ optical upper limit
  44. GRB 250814B: Fermi GBM Final Real-time Localization
  45. GRB 250813A: AstroSat CZTI detection
  46. LIGO/Virgo/KAGRA S250814bg: Identification of a GW compact binary merger candidate possibly associated with GRB 250814A detected by Fermi GBM and Swift BAT
  47. GRB 250813B: VLT X-shooter spectroscopic redshift z = 1.752
  48. GRB 250814A: DDOTI Optical Upper Limit
  49. GRB 250813B: EP-FXT counterpart detection
  50. Fermi-LAT Gamma-ray Observations of IceCube-250813A
  51. GRB 250813B: Swift-XRT afterglow detection
  52. GRB 250814A: Swift detection of a burst coincident with a subthreshold GW trigger
  53. GRB 250814A: Fermi GBM Final Real-time Localization
  54. GRB 250813B: SVOM/COLIBRÍ (FM-GFT) optical observations
  55. GRB 250813B: Ondrejov D50 fast decay
  56. GRB 250813B: SVOM detection of a bright long burst (Correction for GCN 41352).
  57. GRB 250813B: Ondrejov D50 optical afterglow detection
  58. GRB 250813B: SVOM detection of a bright long burst
  59. LIGO/Virgo/KAGRA S250813k: NED Galaxies in the 4-Update Localization Volume
  60. LIGO/Virgo/KAGRA S250813k: Updated Sky localization
  61. EP250812a: Nickel optical upper limit
  62. GRB 250812A: VLT X-shooter spectroscopic redshift confirmation z = 2.571
  63. GRB 250812A: NTT spectroscopic redshift z = 2.57
  64. GRB250812a: STEP/T80S Indication of slow decay of afterglow
  65. EP250812a: NOT, NTT, and GS observations
  66. GRB 250812A: Swift/UVOT Detection
  67. GRB 250813A: Fermi GBM Final Localization
  68. EP250812a: COLIBRÍ detection of the VT candidate and evidence of flattening
  69. EP250812a: Liverpool Telescope upper limits
  70. EP250812a: SVOM/VT optical counterpart
  71. EP250812a: refined analysis of the EP-WXT and EP-FXT observations
  72. IceCube-250813A - IceCube observation of a high-energy neutrino candidate track-like event
  73. IceCube Alert 250813.14: Global MASTER-Net observations report
  74. LIGO/Virgo/KAGRA S250813k: Identification of a GW compact binary merger candidate
  75. GRB 250812A: EP-FXT counterpart detection
  76. GRB 250812A: Swift ToO observations
  77. GRB 250807B: Swift-BAT refined analysis
  78. EP 250812a: GOTO optical upper limit
  79. GRB 250812A: Kilonova-Catcher optical afterglow detection
  80. EP250812a: Swift-XRT counterpart detection
  81. Fermi Gamma-ray Burst Monitor trigger 776705265/250812644 is not a GRB
  82. GRB 250812A: SVOM/COLIBRÍ (FM-GFT) optical observations
  83. EP250812a: Einstein Probe detection of an X-ray transient
  84. GRB 250812A: SVOM/VT optical afterglow confirmation
  85. GRB 250812A: Swift-XRT afterglow detection
  86. GRB 250812A: TRT likely optical counterpart detection
  87. IceCube-Cascade 250809A: Upper limits from a search for additional neutrino events in IceCube
  88. GRB 250812A: SVOM detection of a faint long burst
  89. GRB 250809A: Swift-BAT refined analysis
  90. Fermi Gamma-ray Burst Monitor trigger 776620220/250811660 is not a GRB
  91. Fermi-LAT Gamma-ray Observations of IceCube-250804A
  92. GRB 250807A: Swift-BAT refined analysis
  93. LIGO/Virgo/KAGRA S250810ck: Updated Sky localization and EM Bright Classification
  94. GRB 250809A: Swift/UVOT Detection
  95. LIGO/Virgo/KAGRA S250810ck: Identification of a GW compact binary merger candidate
  96. Corrected Swift-XRT Refined Analysis of GRB 250809A
  97. GRB 250809A: Swift-XRT refined Analysis
  98. GRB 250807B: SVOM/VT optical observation
  99. EP250807a: EP-FXT follow-up observation upper limit
  100. GRB 250809A: LCOGT Optical Upper Limits

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