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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 250314A: EP-FXT afterglow detection
  2. EP250315a: refined analysis of the EP-WXT and EP-FXT observations
  3. GRB 250314A: Swift/UVOT Upper Limits
  4. GRB 250312B: GRBAlpha detection
  5. GRB 250313.89 / Fermi trigger 763594063: bright OT AT 2025ehi detection
  6. GRB 250314A: Swift XRT Detection
  7. EP250315a: optical counterpart candidate detected by Gemini North
  8. GRB 250314A: VLT/X-shooter dropout, redshift z ~ 7.3
  9. EP250315a: Einstein Probe detection of an X-ray transient
  10. GRB 250226A: Mondy AZT-33IK and Koshka Zeiss-1000 Optical Upper Limits
  11. SVOM/MXT upper limit on GRB 250314A
  12. GRB 250314A: SVOM/VT upper limit
  13. GRB 250314A: NOT near-infrared candidate counterpart
  14. GRB 250313A: Fermi GBM Detection
  15. GRB 250313A: CALET Gamma-Ray Burst Monitor detection
  16. GRB 250312B: Fermi GBM Observation
  17. GRB 250313A: Swift-XRT observations
  18. GRB250314A: SVOM/VT lack of bright optical candidate from VHF data
  19. Konus-Wind detection of GRB 250313A
  20. Konus-Wind detection of GRB 250308A
  21. GRB 250314A: SVOM detection of a burst
  22. EP250311a/GRB 250311A: Correction to EP-WXT detection time
  23. GRB 250313B: SVOM/GRM observation of a soft bright short burst
  24. GRB 250313A: SVOM/GRM observation of a bright long burst
  25. FRB 20250206A: Nondetection of Repeating Bursts from FRB 20250206A with FAST
  26. GRB 250313A: AstroSat CZTI detection of a bright long burst
  27. IceCube-250309A: MASTER detection of J140105.33-091631.6 blazar flare with Zhirkov effect
  28. Fermi trigger No 763581136: Global MASTER-Net observations report
  29. GRB 250313A: Fermi-LAT detection
  30. GRB 250313A: Swift ToO observations
  31. EP250304a: Pan-STARRS r and i-band imaging and photometry
  32. GRB 250312B: Swift/BAT-GUANO localization skymap of a burst
  33. EP trigger ID 01709061302: Lick/Kast spectroscopy with the 3 m Shane telescope
  34. Fermi GRB 250313A: Global MASTER-Net observations report
  35. GRB 250309B: PRIME near-infrared upper limits in 2nd epoch
  36. GRB 250313A???: BALROG localization (Fermi Trigger / GRB 250313607)
  37. GRB 250313A: Fermi GBM Final Real-time Localization
  38. The EP-WXT trigger 01709132551 is not a real source
  39. EP250304a: SVOM/VT optical observation
  40. EP250311a/GRB 250311A: EP-FXT follow-up observation
  41. ATCA detection of the radio counterpart of GRB 250309B-AT2025dws
  42. EP250302a: Chandra X-ray Detection
  43. GRB 250312A: Swift-XRT refined Analysis
  44. Fermi Gamma-ray Burst Monitor trigger 763509110/250312911 is not a GRB
  45. Fermi trigger No 763509110: Global MASTER-Net observations report
  46. Fermi GRB 250312B: Global MASTER-Net observations report
  47. GRB 250312A: Enhanced Swift-XRT position
  48. GRB 250312B: Fermi GBM Final Localization
  49. LIGO/Virgo/KAGRA S250304cb: Upper limits from Swift/BAT-GUANO
  50. GRB 250226B: Fermi GBM Observation
  51. Swift GRB 250312A: Global MASTER-Net observations report
  52. GRB 250302A: Fermi GBM Observation
  53. GRB 250309B/AT2025dws: Daochen/RC-10 optical counterpart observation
  54. GRB 250312A: Swift detection of a burst
  55. GRB 241213A: VIRT Optical Upper Limit
  56. GRB 241228A: VIRT Optical Upper Limit
  57. GRB 250311A/EP250311a: Optical upper limits with Kinder observations
  58. GRB 250223B: Fermi GBM Observation
  59. GRB 250311A: Swift-XRT observations
  60. GRB 250228A: Fermi GBM Observation
  61. GRB 250309B: 1.3m DFOT Optical observations
  62. IceCube-250309A: Upper limits from a search for additional neutrino events in IceCube
  63. EP250311a: Global MASTER-Net observations report
  64. GRB 250308A: Swift/BAT-GUANO localization skymap of a short burst
  65. GRB 250302A: Swift/BAT-GUANO localization skymap of a burst
  66. GRB 250228A: Swift/BAT-GUANO localization skymap of a likely short burst
  67. GRB 250226B: Swift/BAT-GUANO localization skymap of a likely long GRB
  68. GRB 250226A: Swift/BAT-GUANO localization skymap of a long GRB
  69. GRB 250223B: Swift/BAT-GUANO localization skymap of a short burst
  70. GRB 250309B: PRIME near-infrared detection
  71. EP250304a: Chandra detection
  72. GRB 250225B: Swift-BAT refined analysis
  73. GRB 250311A/EP250311a: TRT optical upper limit
  74. IceCube-250309A: MITSuME Akeno and Seimei/TriCCS optical observations
  75. GRB 250311A: Tiled Swift observations
  76. EP250311a/GRB 250311A: EP-WXT detection
  77. GRB 250308A: CALET Gamma-Ray Burst Monitor detection
  78. GRB 250311B: SVOM detection of a burst
  79. GRB 250309B: SVOM/VT optical observation
  80. GRB 250311A/MAXI J1457-026: MAXI/GSC detection
  81. The EP-WXT trigger 01709132425 is not a real source
  82. GRB 250309B / AT2025dws: further SAO RAS optical observations
  83. IceCube-250309A: Upper limits from Fermi-GBM Observations
  84. EP250308a: 1.6m Mephisto optical upper limits
  85. Konus-Wind detection of GRB 250309B
  86. GRB 250309B / AT2025dws: KMTNet-CTIO optical observations
  87. IPN triangulation of GRB 250308A (short)
  88. IPN triangulation of GRB 250309B
  89. IceCube-241224A: MASTER detection of PKS 1217+02 blazar flare with Zhirkov effect
  90. GRB 250309B/AT2025dws : COLIBRÍ Detection of the Optical Counterpart
  91. GRB 250309B: Swift-XRT refined Analysis
  92. GRB 250309B / IceCube-250309A: GECAM-B observations
  93. GRB 250309B / AT2025dws: OSIRIS+/GTC spectroscopy z=1.898
  94. Liverpool Telecope observations of AT 2025dws / GRB 250309B
  95. GRB 250309B / AT2025dws: SAO RAS optical observations
  96. GRB 250309B / AT2025dws: Swift-UVOT detection
  97. AT 2025dws, likely optical counterpart of GRB 250309B: LCO confirmation of fast fading
  98. GRB 250309B: Fermi GBM Observation
  99. Fermi GRB 250309B: Global MASTER-Net observations report
  100. Fermi GRB 250309A: Global MASTER-Net observations report

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