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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"

24897 results found.

  1. GRB 250702D, C, E: Swift/BAT-GUANO localization skymap of a burst or galactic transient
  2. GRB 250702F: Enhanced Swift-XRT position
  3. GRB 250702F: NOT observations of the optical afterglow
  4. GRB 250702F: Swift detection of a burst with an optical counterpart
  5. Fermi GBM Triggers 250702B, C, D and E are likely from the same source
  6. GRB 250702A: Fermi GBM Detection
  7. LIGO/Virgo/KAGRA S250702n: Identification of a GW compact binary merger candidate
  8. GRB 250702A: BALROG localization (Fermi Trigger 773142852 / GRB 250702413)
  9. LIGO/Virgo/KAGRA S250701bq: Identification of a GW compact binary merger candidate
  10. LIGO/Virgo/KAGRA S250701bp: Identification of a GW compact binary merger candidate
  11. GRB 250628B: Swift-XRT observations
  12. GRB 250628B: EP-FXT counterpart detection
  13. LIGO/Virgo/KAGRA S250629bs: Updated Sky localization
  14. LIGO/Virgo/KAGRA S250629ae: Updated Sky localization
  15. LIGO/Virgo/KAGRA S250629bs: Identification of a GW compact binary merger candidate
  16. LIGO/Virgo/KAGRA S250629ae: Identification of a GW compact binary merger candidate
  17. LIGO/Virgo/KAGRA S250628am: Updated Sky localization
  18. GRB 250628A: REM optical/NIR upper limits
  19. LIGO/Virgo/KAGRA S250628am: Identification of a GW compact binary merger candidate
  20. GRB 250628B: SVOM detection of a long burst
  21. GRB 250628A: VLT/X-shooter upper limits
  22. GRB 250628A: Swift/UVOT Upper Limits
  23. GRB 250628A: Swift-XRT refined Analysis
  24. GRB 250628A: Enhanced Swift-XRT position
  25. GRB 250628A: Swift detection of a burst
  26. GRB 250625A: Swift-BAT refined analysis
  27. GRB 250625A: Leavitt Observatory afterglow detection
  28. GRB 250625A: AbAO and INASAN Kislovodsk Optical Observations
  29. GRB 250625A: SVOM/C-GFT upper limit in early phase
  30. GRB 250625A: Swift/UVOT Upper Limits
  31. GRB 250625A: ABObservatory afterglow detection
  32. GRB 250625A: OHP/T193 optical detection
  33. GRB 250625A: COLIBRÍ optical observations
  34. GRB 250625A: Swift-XRT refined Analysis
  35. GRB 250625A: JinShan optical observations
  36. GRB250625A: Fermi GBM Observation
  37. GRB 250620B: Fermi GBM Observation
  38. GRB 250625A: SAO RAS possible optical afterglow
  39. GRB 250625A: Enhanced Swift-XRT position
  40. GRB 250625A: Swift detection of a burst
  41. GRB 250617B: Mondy and SAO RAS optical observations on 2025-06-23, 2025-06-24
  42. GRB 241018A: Maidanak optical observations
  43. GRB 250620C: AstroSat CZTI detection
  44. Fermi GRB 250624A: Global MASTER-Net observations report
  45. GRB 250521A: VZLUSAT-2 detection
  46. GRB 250617B: Swift-BAT refined analysis
  47. Fermi trigger No 772190032: Global MASTER-Net observations report
  48. IPN triangulation of GRB 250620С (long/bright)
  49. GRB 250620C: SVOM/GRM observation
  50. GRB 250620A: SVOM/GRM observation of a short burst
  51. GRB250620A: Fermi GBM Observation
  52. GRB 250617B: Calapai Observatory, Massa S. Giorgio (Messina), optical observation.
  53. GRB 250619B: Fermi GBM Observation
  54. GRB 250620B: Swift/BAT-GUANO localization skymap of a burst
  55. GRB250620C: Fermi GBM Observation
  56. GRB 250620A: Swift/BAT-GUANO subthreshold detection of a possibly short burst
  57. GRB 250619B: Swift/BAT-GUANO localization skymap of a burst
  58. Fermi trigger No 772128434: Global MASTER-Net observations report
  59. EP-WXT trigger 01709179036: a new outburst of GRS 1739-278
  60. GRB 250617B: Nickel telescope optical observations
  61. GRB 250615A: Kilonova-Catcher optical upper limits
  62. GRB 250617B: Assy AZT-20 Optical Observations
  63. GRB 250612A / Swift J1643.6−3854: Swift-BAT refined analysis
  64. Fermi GRB 250617A: Global MASTER-Net observations report
  65. sb25061218/SVOM: OHP/T120 and OHP/T193 optical imaging and spectroscopic observations
  66. GRB 250617B: Swift/UVOT Detection
  67. GRB 250617B: Kilonova-Catcher optical afterglow detection
  68. GRB 250617B: VLT/X-shooter spectroscopic redshift z = 1.396
  69. GRB 250617B: COLIBRÍ optical observations
  70. GRB 250617B: NOT NIR observations of the afterglow
  71. GRB 250617B: Swift-XRT refined Analysis
  72. GRB 250617B: NUTTelA-TAO early time optical observations
  73. GRB 250617B: Enhanced Swift-XRT position
  74. GRB 250617B: Fermi GBM Observation
  75. GRB 250615A: Swift-BAT refined analysis
  76. GRB 250617B: SAO RAS optical observations
  77. GRB 250617B: Swift detection of a burst with an optical counterpart
  78. GRB 250615A: Calapai Observatory, Massa S. Giorgio (Messina), upper limit
  79. EP#01709178975: Swift-XRT counterpart detection
  80. EP-WXT trigger 01709178975: GOTO optical upper limit
  81. GRB 250615A / EP250615a: AstroSat CZTI detection
  82. SVOM sb25061207: AbAO AS-32 Optical Upper Limit
  83. GRB 250615A: COLIBRÍ optical upper limit
  84. GRB 250615A: DDOTI Optical Upper Limit
  85. GRB 250615A: Swift/UVOT Upper Limits
  86. GRB 250615A: Swift-XRT refined Analysis
  87. sb25061207/SVOM: T120 OHP optical upper limit
  88. EP250615a/GRB 250615A: EP-WXT detection of a fast X-ray transient
  89. EP-WXT trigger 01709178875: confirmation of a stellar flare by BOOTES-6
  90. GRB 250615A: Enhanced Swift-XRT position
  91. GRB 250615A: Swift detection of a burst
  92. Fermi trigger No 771718064: Global MASTER-Net observations report
  93. sb25061207: Mephisto optical upper limits
  94. EP250612a / GRB 250612B: NOT optical observations of the afterglow candidate
  95. sb25061218: SVOM/COLIBRÍ (FM-GFT) optical upper limits
  96. sb25061207: SVOM/COLIBRÍ (FM-GFT) optical upper limit
  97. sb25061218: Swift-XRT observations
  98. EP250612a: refined analysis of the EP-WXT and EP-FXT observations
  99. GRB 250610B: J band upper limit by SYSU 80cm infrared telescope
  100. sb25061207: EP-FXT follow-up observation and afterglow candidate

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