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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"

20978 results found.

  1. GRB 250819A: SVOM/GRM observation of a possible “long” duration type I burst
  2. LIGO/Virgo/KAGRA S250818k: WINTER J-band observations of AT 2025ulz
  3. GRB 250818B: 10 GHz VLA detection
  4. LIGO/Virgo/KAGRA S250818k: Pan-STARRS grizy-band imaging and photometry of AT2025ulz
  5. LIGO/Virgo/KAGRA S250818k: Swift observations of AT 2025ulz
  6. LIGO/Virgo/KAGRA S250818k: Multi-band Gemini GMOS Detections
  7. LIGO/Virgo/KAGRA S250818k: ATLAS pre-discovery limits for AT2025ulz
  8. GRB 250814A: Swift/UVOT Upper Limits
  9. GRB 250813B: Swift/UVOT Upper Limit
  10. GRB 250818B: FTW optical and NIR observations show reddening of the counterpart
  11. GRB 250818B: Kilonova-Catcher optical afterglow detection
  12. GRB 250818B: Liverpool Telescope optical detections
  13. LIGO/Virgo/KAGRA S250818k: Upper limits from Fermi-GBM Observations
  14. LIGO/Virgo/KAGRA S250818k: Pan-STARRS pre-detection limits for AT2025ulz
  15. LIGO/Virgo/KAGRA S250818k: Keck I LRIS spectroscopy of ZTF25abjmnps (AT2025ulz)
  16. GRB 250818B: Swift/UVOT Detection
  17. LIGO/Virgo/KAGRA S250818k: FTW Fast reddening of AT 2025ulz
  18. GRB 250818B: optical afterglow detection with Lesedi (GOTO25fzq)
  19. GRB 250818B: TRT Optical Observation
  20. Fermi GRB 250816A: Global MASTER-Net observations report
  21. GRB 250818B: SAO RAS optical observations
  22. Swift GRB 250818A: Global MASTER-Net observations report
  23. GRB 250818B: NOT optical observations
  24. LIGO/Virgo/KAGRA S250818k: FTW optical and NIR observations of AT 2025ulz
  25. Fermi trigger No 776849714: Global MASTER-Net observations report
  26. GRB 250818B: KAIT optical observations
  27. GRB 250818A: Swift/UVOT Upper Limits
  28. LIGO/Virgo/KAGRA S250818k: Candidates from the Zwicky Transient Facility
  29. GRB 250813B: SVOM/ECLAIRs refined analysis
  30. LIGO/Virgo/KAGRA S250818k: Coverage and upper limits from MAXI/GSC observations
  31. GRB 250818B: SVOM/VT optical observation
  32. GRB 250814A: Further GRAWITA TNG NIR observations
  33. GRB 250818B: Swift-XRT afterglow detection
  34. GRB 250818B: GOTO optical counterpart candidate
  35. sb25081602: Swift-XRT observations
  36. Fermi GRB 250814B: Global MASTER-Net observations report
  37. GRB 250813B: Liverpool Telescope optical upper limits
  38. GRB 250814A: detection of the afterglow candidate with Liverpool Telescope
  39. GRB 250814A: GRAWITA TNG NIR observations
  40. GRB 250812A: SVOM/VT optical continued observation
  41. GRB 250814A: Mondy optical observations of the candidate counterpart to LVK S250814bg
  42. GRB 250813B: Calapai Observatory, Massa S. Giorgio (Messina), upper limit
  43. LIGO/Virgo/KAGRA S250813k: Swift XRT observations, 2 X-ray sources
  44. GRB 250814A: P200/WIRC observations of the afterglow candidate
  45. GRB 250814A: possible optical afterglow candidate at Spanish observatories
  46. GRB 250814A: Possible afterglow candidate from P200/WIRC
  47. GRB 250814A: Optical observations with MDM Hiltner 2.4m telescope
  48. Fermi trigger No 776818276: Global MASTER-Net observations report
  49. Swift GRB250814.32: Global MASTER-Net observations report
  50. GRB 250814A: J-band upper limit from WINTER
  51. GRB 250813B: NOT observations of the optical afterglow
  52. GRB 250813B: SVOM/VT optical observations
  53. GRB 250813B: VLT X-shooter spectroscopic redshift z = 1.752
  54. GRB 250814A: DDOTI Optical Upper Limit
  55. Fermi-LAT Gamma-ray Observations of IceCube-250813A
  56. GRB 250813B: SVOM/COLIBRÍ (FM-GFT) optical observations
  57. GRB 250813B: Ondrejov D50 fast decay
  58. LIGO/Virgo/KAGRA S250813k: NED Galaxies in the 4-Update Localization Volume
  59. EP250812a: Nickel optical upper limit
  60. GRB 250812A: VLT X-shooter spectroscopic redshift confirmation z = 2.571
  61. GRB250812a: STEP/T80S Indication of slow decay of afterglow
  62. EP250812a: NOT, NTT, and GS observations
  63. GRB 250812A: Swift/UVOT Detection
  64. EP250812a: COLIBRÍ detection of the VT candidate and evidence of flattening
  65. EP250812a: SVOM/VT optical counterpart
  66. EP250812a: refined analysis of the EP-WXT and EP-FXT observations
  67. IceCube Alert 250813.14: Global MASTER-Net observations report
  68. GRB 250812A: Swift ToO observations
  69. EP 250812a: GOTO optical upper limit
  70. GRB 250812A: Kilonova-Catcher optical afterglow detection
  71. EP250812a: Swift-XRT counterpart detection
  72. GRB 250812A: SVOM/COLIBRÍ (FM-GFT) optical observations
  73. GRB 250812A: SVOM/VT optical afterglow confirmation
  74. GRB 250812A: Swift-XRT afterglow detection
  75. GRB 250812A: TRT likely optical counterpart detection
  76. Fermi-LAT Gamma-ray Observations of IceCube-250804A
  77. GRB 250809A: Swift/UVOT Detection
  78. GRB 250702B: Chandra X-ray Detection
  79. EP250807a: Global MASTER-Net observations report
  80. Fermi GRB 250808A: Global MASTER-Net observations report
  81. GRB 250808A: SVOM/COLIBRÍ (FM-GFT) optical upper limit
  82. GRB 250808A: Swift-XRT candidate counterpart detection
  83. GRB 250807A: SVOM/VT optical continued observation
  84. EP-WXT trigger 01709195487: KAIT confirmation of the stellar flare
  85. GRB 250807B: Swift/UVOT Detection
  86. GRB 250807B: Kilonova-Catcher optical afterglow detection
  87. GRB 250807A: Swift/UVOT Detection
  88. EP250807a: NTT z-band optical upper limit
  89. GRB 250806A: Mondy optical observations, and nearby bright galaxy photometry
  90. Swift GRB250807.45: Global MASTER-Net observations report
  91. GRB 250807B: NTT optical observations
  92. EP250807a: EP-WXT detection of a fast X-ray transient
  93. EP 250807.979: GOTO optical upper limit
  94. GRB 250807A: SVOM/VT optical observation
  95. EP250806a: Upper limit from Fermi-GBM Observations
  96. Swift GRB250807.65: Global MASTER-Net observations report
  97. GRB 250805A: Kilonova-Catcher optical upper limits
  98. GRB 250805A: Swift/UVOT Upper Limits
  99. GRB 250806A: Swift/UVOT U-band detection
  100. IceCube Alert 250804.84: Global MASTER-Net observations report

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