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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"

4925 results found.

  1. GRB 251011B inspection: MASTER orphan GRB detection
  2. GRB 251011A: AstroSat CZTI detection
  3. GRB 251011A: Fermi GBM Final Real-time Localization
  4. GRB 251003A: Fermi GBM Observation
  5. GRB 251007A: AKO Optical Upper Limit
  6. EP251003a: LCO and VST fading optical counterpart
  7. Fermi GRB 251006B: Global MASTER-Net observations report
  8. GRB 251003A: LAST optical observations
  9. GRB 251002A: Mondy/AZT-33IK optical observations
  10. GRB 251002A: NIR observations with WINTER
  11. Fermi GBM Sub-Threshold Detection of GRB 250910A
  12. GRB 251001B: COLIBRÍ further observations and evidence of a multi-wavelength shallow decay
  13. GRB 251003A: COLIBRÍ photometric redshift
  14. GRB 251003A: GOTO detection of the optical counterpart
  15. GRB 251002A: GOTO detection of optical counterpart
  16. GRB 251003A: GTC/OSIRIS+ spectroscopic redshift z = 4.412
  17. GRB 251002A: AbAO optical observations
  18. GRB 251002A: SVOM/COLIBRÍ (FM-GFT) optical observations
  19. GRB 251002A: VLT/X-shooter spectroscopic redshift z = 2.178
  20. GRB 251003A: LCOGT Optical Detection
  21. GRB 251003A: COLIBRÍ optical detection of the fading afterglow
  22. Swift GRB251003A: Global MASTER-Net observations report
  23. GRB 251001B: SVOM/VT optical observation
  24. GRB 250910A / EP250910a: VLT/X-shooter host galaxy redshift z = 0.592
  25. GRB 250925A/EP250925a: EP-WXT detection
  26. GRB 250919A / EP250919a: Global MASTER Net before, during and after trigger optical observations
  27. GRB 250924A: Swift/UVOT Detection
  28. GRB 250924A: COLIBRÍ optical observations
  29. GRB 250924A: Swift detection of a burst with an optical counterpart
  30. Fermi GRB 250922B: Global MASTER-Net observations report
  31. Fermi trigger No 780156732: Global MASTER-Net observations report
  32. GRB 250922A: Fermi GBM Final Localization
  33. GRB 250920B: Enhanced Swift-XRT position
  34. GRB 250920C: GOTO optical counterpart candidate
  35. GRB 250919A / EP250919a: MASTER bright afterglow detection 24h after GRB time
  36. EP250919a: Global MASTER-Net observations report
  37. EP250916a: EP-FXT follow-up observation
  38. GRB 250916A: GOTO optical counterpart candidate
  39. GRB250912A: VLT/HAWK-I follow-up observations
  40. EP250911a: refined analysis of the EP-WXT and EP-FXT observations
  41. EP250910a: Global MASTER-Net observations report
  42. GRB 250910A: LCO optical upper limit
  43. EP250908c: Global MASTER-Net observations report
  44. SVOM/sb25090605: detection of an X-ray transient from the LMXB 4U 0513-40
  45. EP250905a: Liverpool Telescope i-band upper limits
  46. LIGO/Virgo/KAGRA S250830bp: DECam/SOAR GW-MMADS updates
  47. LIGO/Virgo/KAGRA S250830bp: DECam DESGW Epoch 2 Candidates
  48. IceCube Alert 250905.84: Global MASTER-Net observations report
  49. GRB 250905A: KAIT optical upper limit
  50. IceCube-Cascade 250903A: Upper limits from a search for additional neutrino events in IceCube
  51. GRB 250904A: Prompt enhanced Swift-XRT position
  52. GRB 250904A: Swift detection of a burst
  53. LIGO/Virgo/KAGRA S250904ae: Identification of a GW compact binary merger candidate
  54. GRB 250903A: LCO optical observation
  55. GRB 250903A: LCO optical afterglow detection
  56. EP250903a: LCO candidate counterpart discovery
  57. GRB 250903A: TRT optical counterpart detection
  58. EP250903a: Global MASTER-Net observations report
  59. EP250903a: TRT optical observations
  60. EP250903a: Einstein Probe detection of an X-ray transient
  61. EP 250827B: Detection of supernova counterpart by LCO.
  62. EP250827b: NOT spectroscopic observations and AT 2025wkm classification as a broad-lined type-Ic supernova
  63. EP250827b: continued Liverpool Telescope observations
  64. Fermi GRB 250902B: Global MASTER-Net observations report
  65. LIGO/Virgo/KAGRA S250902av: 1 counterpart neutrino candidate event from an IceCube neutrino search
  66. GRB 250901A: EP-FXT follow-up observation
  67. EP250901a: Swift-XRT observations
  68. LIGO/Virgo/KAGRA S250830bp: DECam GW-MMADS candidates
  69. LIGO/Virgo/KAGRA S250830bp: DECam DESGW Epoch 1 Candidates
  70. EP250901a: Mephisto optical upper limits
  71. EP250901a: Einstein Probe detection of an X-ray transient
  72. GRB 250831A: Swift-XRT counterpart detection
  73. GRB 250830B: MAXI/GSC detection
  74. LIGO/Virgo/KAGRA S250830m: Identification of a GW compact binary merger candidate
  75. LIGO/Virgo/KAGRA S250725j: Observations with the NSF-DOE Vera C. Rubin Observatory
  76. Fermi GRB 250827A: Global MASTER-Net observations report
  77. EP250827a: Global MASTER-Net observations report
  78. Fermi GRB 250824B: Global MASTER-Net observations report
  79. LIGO/Virgo/KAGRA S250818k: ENGRAVE observations of SN 2025ulz as a type II supernova
  80. LIGO/Virgo/KAGRA S250818k: COLIBRÍ confirmation of rebrightening of AT2025ulz
  81. GRB 250812A: SVOM/ECLAIRs refined analysis
  82. EP250821a: VLT X-shooter spectroscopic redshift z = 0.577
  83. LIGO/Virgo/KAGRA S250818k: WFST pre-discovery limits and follow-up observations of AT 2025ulz
  84. LIGO/Virgo/KAGRA S250818k: WINTER J-band observations of AT 2025ulz
  85. IPN triangulation of GRB 250814C (short)
  86. GRB 250818B: Liverpool Telescope optical detections
  87. GRB 250818B: Swift/UVOT Detection
  88. GRB 250818B: NOT optical observations
  89. Fermi trigger No 776849714: Global MASTER-Net observations report
  90. GRB 250818B: GOTO optical counterpart candidate
  91. sb25081602: Swift-XRT observations
  92. SVOM/sb25081602: detection of a likely X-ray transient
  93. GRB 250813B: Liverpool Telescope optical upper limits
  94. GRB 250814A: Further COLIBRÍ optical upper limit
  95. GRB 250814A: P200/WIRC observations of the afterglow candidate
  96. Fermi trigger No 776818276: Global MASTER-Net observations report
  97. IceCube-250813A: Upper limits from a search for additional neutrino events in IceCube
  98. Fermi-LAT Gamma-ray Observations of IceCube-250813A
  99. EP250812a: Liverpool Telescope upper limits
  100. EP250812a: SVOM/VT optical counterpart

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