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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"

3533 results found.

  1. EP250427a: Lesedi optical counterpart detection
  2. EP250427A: COLIBRÍ Continuing Optical Observations
  3. EP250427a: LT optical counterpart detection
  4. EP250421a: Upper limits from Fermi-GBM Observations
  5. IceCube-250421A: DDOTI Detection of the LAST Candidate
  6. Fermi GRB 250421A: Global MASTER-Net observations report
  7. EP250421a: Einstein Probe detection of an X-ray transient
  8. IceCube Alert 250421.71: Global MASTER-Net observations report
  9. EP250416a: Global MASTER-Net observations report
  10. SVOM/sb25041603: SVOM detection of an X-ray transient
  11. EP250304a: ATCA radio observations
  12. Fermi trigger No 766148493: Global MASTER-Net observations report
  13. Fermi trigger No 766173972: Global MASTER-Net observations report
  14. Fermi GRB 250407A: Global MASTER-Net observations report
  15. IPN triangulation of GRB 250406B (short/hard)
  16. IceCube Alert 250406.95: Global MASTER-Net observations report
  17. Fermi trigger No 765619921: Global MASTER-Net observations report
  18. GRB 250404A / EP250404a: SVOM/GWAC-F60 and F50 observations
  19. EP250404a / GRB 250404A: J band observations by SYSU 80cm telescope
  20. GRB 250404A / EP250404a: Mondy optical observations
  21. Fermi GRB 250404A: Global MASTER-Net observations report
  22. EP250404a: Global MASTER-Net observations report
  23. GRB 250327B: VIRT Optical Upper Limit
  24. GRB 250402A: Mondy optical observations
  25. Fermi GRB 250403A: Global MASTER-Net observations report
  26. GRB 250403A: GOTO optical counterpart follow-up observations
  27. GRB 250403A: GOTO detection of the optical afterglow
  28. GRB 250402A: REM optical/NIR upper limits
  29. GRB 250328A: AbAO AS-32 Optical Observations
  30. GRB 250322B possible detection by the AstroSat Satellite
  31. GRB 250331B: Swift detection of a burst
  32. GRB 250328A: 1.6m Mephisto optical observations
  33. IceCube Alert 250330.35: Global MASTER-Net observations report
  34. GRB 250327B: MASTER detection of OT rebrightening
  35. GRB 250327B: LCO optical counterpart detection
  36. FRB 20250316A: FTW optical observations
  37. GRB 250327B: further optical observations by LCOGT
  38. GRB 250327b: Liverpool Telescope optical observations
  39. LIGO/Virgo/KAGRA S250328ae: Identification of a GW compact binary merger candidate
  40. GRB 250327B: SVOM/COLIBRÍ (F-GFT) follow-up observations
  41. GRB 250327B: SAO RAS optical candidate
  42. EP250321a: Xinglong 216 decaying optical observations
  43. GRB 250321B: SVOM detection of a sub-threshold transient event
  44. LIGO/Virgo/KAGRA S250319bu: Identification of a GW compact binary merger candidate
  45. GRB 250317B: Mondy AZT-33IK Optical Observations
  46. Fermi trigger No 763933627: Global MASTER-Net observations report
  47. GRB 250314A: REM optical/NIR upper limits
  48. GRB 250317B: LCO detection of the fading optical afterglow
  49. GRB 250313.89 / Fermi trigger 763594063: bright OT AT 2025ehi detection
  50. GRB 250314A: VLT/X-shooter dropout, redshift z ~ 7.3
  51. GRB 250226A: Mondy AZT-33IK and Koshka Zeiss-1000 Optical Upper Limits
  52. GRB250314A: SVOM/VT lack of bright optical candidate from VHF data
  53. Fermi GRB 250313A: Global MASTER-Net observations report
  54. Fermi GRB 250312B: Global MASTER-Net observations report
  55. GRB 241228A: VIRT Optical Upper Limit
  56. GRB 250311A/EP250311a: Optical upper limits with Kinder observations
  57. GRB 250228A: Fermi GBM Observation
  58. GRB 250225B: Swift-BAT refined analysis
  59. GRB 250311A/MAXI J1457-026: MAXI/GSC detection
  60. GRB 250309B / AT2025dws: OSIRIS+/GTC spectroscopy z=1.898
  61. GRB 250309B / AT2025dws: SAO RAS optical observations
  62. AT 2025dws, likely optical counterpart of GRB 250309B: LCO confirmation of fast fading
  63. IceCube Alert 250309.32: Global MASTER-Net observations report
  64. EP250308a: FTW optical and NIR upper limits
  65. GRB 250305A: AstroSat CZTI detection
  66. EP250302a:Xinglong optical observations
  67. Fermi trigger No 762963055: Global MASTER-Net observations report
  68. GRB 250305A: SVOM/GRM observation of a burst
  69. GRB 250305A: Fermi GBM Final Real-time Localization
  70. EP250302a: Mondy Continued Optical Observations
  71. LIGO/Virgo/KAGRA S250304cb: Identification of a GW compact binary merger candidate
  72. EP250304a: Global MASTER-Net observations report
  73. GRB 250226A: GRANDMA Optical Observations
  74. Fermi GRB 250302A: Global MASTER-Net observations report
  75. EP250302a: FTW optical and NIR detection
  76. GRB 250228A: Fermi GBM Final Localization
  77. Konus-Wind detection of GRB 250226A
  78. GRB 250226A: KAO Optical Upper Limit
  79. GRB 250226A: AbAO AS-32 Optical Upper Limit
  80. EP250227a: Global MASTER-Net observations report
  81. EP250227a: TRT optical upper limit
  82. GRB 250225B: VLT/HAWKI near-infrared observations
  83. EP250227a: Optical upper limits with Kinder observations
  84. EP250228a: Swift/XRT localisation
  85. EP250228a: Global MASTER-Net observations report
  86. GRB 250226A / EP250226a: LCO detection of the afterglow
  87. LIGO/Virgo/KAGRA S250226dl: Identification of a GW compact binary merger candidate
  88. GRB 250225B: Fermi GBM Observation
  89. GRB 250225B: VLT/FORS2 candidate optical afterglow
  90. EP250226a: Global MASTER-Net observations report
  91. Fermi GRB 250225A: Global MASTER-Net observations report
  92. EP250223a: LCO detection of the afterglow
  93. Fermi trigger No 762020305: Global MASTER-Net observations report
  94. Fermi GRB 250217A: Global MASTER-Net observations report
  95. GRB 250215A: Fermi GBM Observation
  96. EP250215a: Global MASTER-Net observations report
  97. GRB 250205A: Leavitt Observatory optical upper limit
  98. Integral GRB250211.89: Global MASTER-Net observations report
  99. EP250207b: Global MASTER-Net observations report
  100. LIGO/Virgo/KAGRA S250206dm: Global MASTER-Net observations report

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